Direct Path Reads instead of Sequential Reads for index range scan
Database is 11.2. I have two development schemas, with the same table loaded in each schema - a 5 million row table. The execution path for the sql statement is the same against both tables; it's doing an index range scan.
But it would appear Oracle performs a direct path read against one schema, and performs sequential reads against the other schema. I don't understand why I'm seeing different behavior when the execution plan is the same. Any ideas? These are two different schemas in the same database.
There is not enough information.So you even these tables located same database and you gathered statistics it is not mean both run time wait event statistics must be same.Really they are different tables.If both query use INDEX RANGE SCAN the it is not mean these plans are same.What about table and their index statistics? are they same? for example num_row or num_blocks of both tables are same? also about indexes.In additionally if you want to get exact reason you can enable sql trace(using dbms_monitor or setting sql_trace parameter to true according session) and need analyze result trace file using tkprof utility.In additionally in 11g here when query execution time oracle automatically choose direct read path(serial) based on size of tables and size of buffer cache(also here is available some hidden parameter to controlling this behavior).
Similar Messages
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Is index range scan the reason for query running long time
I would like to know whether index range scan is the reason for the query running long time. Below is the explain plan. If so, how to optimise it? Please help
Operation Object COST CARDINALITY BYTES
SELECT STATEMENT () 413 1000 265000
COUNT (STOPKEY)
FILTER ()
TABLE ACCESS (BY INDEX ROWID) ORDERS 413 58720 15560800
INDEX (RANGE SCAN) IDX_SERV_PROV_ID 13 411709
TABLE ACCESS (BY INDEX ROWID) ADDRESSES 2 1 14
INDEX (UNIQUE SCAN) SYS_C004605 1 1
TABLE ACCESS (BY INDEX ROWID) ADDRESSES 2 1 14
INDEX (UNIQUE SCAN) SYS_C004605 1 1
TABLE ACCESS (BY INDEX ROWID) ADDRESSES 2 1 14
INDEX (UNIQUE SCAN) SYS_C004605 1 1The index range scan means that the optimiser has determined that it is better to read the index rather than perform a full table scan. So in answer to your question - quite possibly but the alternative might take even longer!
The best thing to do is to review your query and check that you need every table included in the query and that you are accessing the tables via the best route. For example if you can access a table via primary key index that would be better than using a non-unique index. But the best way of reducing the time the query takes to run is to give it less tables (and indexes) to read.
John Seaman
http://www.asktheoracle.net -
Query Tuning (sequential read + direct path read/write temp)
Following query takes nearly 10 minutes under 10.2.0.2 on WIN2K3 to execute but I am sure there would be an alternate to tune it further.
Major waits are 'db file sequential read' and 'direct path read temp' in addition to 'direct path write temp'
Increasing/tuning the work_area_policy/sort_area_size would help? moving the tables to faster disk would reduce PIO causing sequential read, query re-writing would prove to be helpful?.
Below is the tkprof:
SELECT
P.PER_ID
, CL.DESCR
, P.ENG_NAME
, P.ARA_NAME
, P.NATION
, P.ADDR
, ('Mob:' || NVL(P.MOB, '') || ', Home:' || NVL(P.HOME, '') || ', Bus.:' || NVL(P.BUS, '') || ', Fax:' || NVL(P.FAX, '')) PHONE
, SUM(CASE
WHEN FT.FT_TYPE_FLG IN ('BS','BX','AD','AX') THEN FT.CUR_AMT
ELSE 0
END) BILL
, SUM(CASE
WHEN FT.FT_TYPE_FLG IN ('PS','PX') THEN FT.CUR_AMT * -1
ELSE 0
END) PAY
, SUM(FT.CUR_AMT) DUE
, SUM(CASE
WHEN FT.FREEZE_DTTM > '03-JUN-08' THEN
CASE WHEN FT.FT_TYPE_FLG IN ('PS','PX') THEN FT.CUR_AMT * -1
ELSE 0
END
ELSE 0
END) PAY_02JUN
FROM
CI_FT FT
, CI_SA SA
, CI_ACCT_CHAR AC
, CI_CUST_CL_L CL
, CI_ACCT A
, CI_ACCT_PER AP
SELECT
P.PER_ID
, (P.CITY || ', ' || P.STATE || ',' || P.COUNTRY) ADDR
, MAX(DECODE(PP.PHONE_TYPE_CD, 'MOB ', PP.PHONE)) MOB
, MAX(DECODE(PP.PHONE_TYPE_CD, 'BUSN ', PP.PHONE)) BUS
, MAX(DECODE(PP.PHONE_TYPE_CD, 'HOME ', PP.PHONE)) HOME
, MAX(DECODE(PP.PHONE_TYPE_CD, 'FAX ', PP.PHONE)) FAX
, MAX(DECODE(PN.NAME_TYPE_FLG, 'PRIM', PN.ENTITY_NAME)) ENG_NAME
, MAX(DECODE(PN.NAME_TYPE_FLG, 'ALT ', PN.ENTITY_NAME)) ARA_NAME
, MAX(DECODE(PC.CHAR_TYPE_CD, 'NATION ', PC.CHAR_VAL)) NATION
FROM
CI_PER P
, CI_PER_PHONE PP
, CI_PER_NAME PN
, CI_PER_CHAR PC
WHERE
P.PER_ID = PP.PER_ID (+)
AND P.PER_ID = PN.PER_ID (+)
AND P.PER_ID = PC.PER_ID (+)
GROUP BY
P.PER_ID
, (P.CITY || ', ' || P.STATE || ',' || P.COUNTRY)
) P
WHERE
P.PER_ID = AP.PER_ID
AND AP.ACCT_ID = AC.ACCT_ID
AND AP.ACCT_ID = SA.ACCT_ID
AND AP.MAIN_CUST_SW = 'Y'
AND A.ACCT_ID = SA.ACCT_ID
AND A.ACCT_ID = AP.ACCT_ID
AND AC.CHAR_TYPE_CD = 'ACCTYPE'
AND AC.CHAR_VAL IN ('UOS', 'DEFAULT')
AND AC.ACCT_ID = SA.ACCT_ID
AND CL.LANGUAGE_CD = 'ENG'
AND A.ACCT_ID = AC.ACCT_ID
AND A.CUST_CL_CD = CL.CUST_CL_CD
AND SA.SA_ID = FT.SA_ID
AND FT.FREEZE_DTTM IS NOT NULL
GROUP BY
P.PER_ID
, CL.DESCR
, P.ENG_NAME
, P.ARA_NAME
, P.NATION
, P.ADDR
, ('Mob:' || NVL(P.MOB, '') || ', Home:' || NVL(P.HOME, '') || ', Bus.:' || NVL(P.BUS, '') || ', Fax:' || NVL(P.FAX, ''))
HAVING
SUM(FT.CUR_AMT) > 0
call count cpu elapsed disk query current rows
Parse 1 0.64 0.64 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 304 353.09 430.04 21720 52997832 0 4543
total 306 353.73 430.69 21720 52997832 0 4543
Misses in library cache during parse: 1
Optimizer mode: CHOOSE
Parsing user id: 79 (CISADM)
Rows Row Source Operation
4543 FILTER (cr=52997832 pr=21720 pw=10311 time=430019418 us)
5412 HASH GROUP BY (cr=52997832 pr=21720 pw=10311 time=430015729 us)
199471 VIEW (cr=52997832 pr=21720 pw=10311 time=423392346 us)
199471 HASH GROUP BY (cr=52997832 pr=21720 pw=10311 time=423192867 us)
4013304 TABLE ACCESS BY INDEX ROWID CI_FT (cr=52997832 pr=11409 pw=0 time=140469508 us)
17717785 NESTED LOOPS (cr=49295470 pr=8987 pw=0 time=407554071 us)
13704480 NESTED LOOPS (cr=21818135 pr=7655 pw=0 time=287797921 us)
2782119 NESTED LOOPS OUTER (cr=3915432 pr=2950 pw=0 time=38953485 us)
571492 NESTED LOOPS OUTER (cr=2545763 pr=2711 pw=0 time=7433194 us)
286061 NESTED LOOPS OUTER (cr=2253263 pr=2671 pw=0 time=26607373 us)
123411 NESTED LOOPS (cr=1989056 pr=2642 pw=0 time=22711194 us)
123411 NESTED LOOPS (cr=1864959 pr=2642 pw=0 time=20860026 us)
123411 NESTED LOOPS (cr=1494040 pr=1754 pw=0 time=15553373 us)
243088 NESTED LOOPS (cr=29540 pr=1754 pw=0 time=10213331 us)
13227 TABLE ACCESS FULL CI_PER (cr=251 pr=49 pw=0 time=43331 us)
243088 INDEX RANGE SCAN XM150S1 (cr=29289 pr=1705 pw=0 time=6178159 us)(object id 97173)
123411 INLIST ITERATOR (cr=1464500 pr=0 pw=0 time=7220251 us)
123411 INDEX RANGE SCAN CM064S0 (cr=1464500 pr=0 pw=0 time=5631936 us)(object id 108631)
123411 TABLE ACCESS BY INDEX ROWID CI_ACCT (cr=370919 pr=888 pw=0 time=7241286 us)
123411 INDEX UNIQUE SCAN XM148P0 (cr=247508 pr=0 pw=0 time=1198649 us)(object id 97147)
123411 TABLE ACCESS BY INDEX ROWID CI_CUST_CL_L (cr=124097 pr=0 pw=0 time=1391837 us)
123411 INDEX UNIQUE SCAN XC523P0 (cr=686 pr=0 pw=0 time=595005 us)(object id 97745)
283749 TABLE ACCESS BY INDEX ROWID CI_PER_PHONE (cr=264207 pr=29 pw=0 time=3549713 us)
283749 INDEX RANGE SCAN XM172P0 (cr=125886 pr=4 pw=0 time=1307395 us)(object id 98733)
571492 INDEX RANGE SCAN XM171S2 (cr=292500 pr=40 pw=0 time=2976807 us)(object id 98728)
2777066 TABLE ACCESS BY INDEX ROWID CI_PER_CHAR (cr=1369669 pr=239 pw=0 time=23084761 us)
2777066 INDEX RANGE SCAN XM168P0 (cr=596156 pr=53 pw=0 time=7394319 us)(object id 98719)
13704480 TABLE ACCESS BY INDEX ROWID CI_SA (cr=17902703 pr=4705 pw=0 time=163320548 us)
13704480 INDEX RANGE SCAN XM199S1 (cr=5688247 pr=104 pw=0 time=51063061 us)(object id 98973)
4013304 INDEX RANGE SCAN CM112S1 (cr=27477335 pr=1332 pw=0 time=124063022 us)(object id 116797)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 304 0.00 0.00
db file sequential read 11366 0.34 65.63
direct path write temp 1473 0.06 2.91
latch: cache buffers chains 17 0.00 0.00
db file scattered read 7 0.01 0.03
read by other session 2 0.00 0.00
direct path read temp 1473 0.03 6.85
SQL*Net message from client 304 0.02 2.74
SQL*Net more data to client 292 0.00 0.00
********************************************************************************Luckys
I've just realised that I mis-read part of your plan:
199471 HASH GROUP BY (cr=52997832 pr=21720 pw=10311 time=423192867 us)
4013304 TABLE ACCESS BY INDEX ROWID CI_FT (cr=52997832 pr=11409 pw=0 time=140469508 us)
17717785 NESTED LOOPS (cr=49295470 pr=8987 pw=0 time=407554071 us)The time component for a line is the time it supplies, plus the sum of the time from its direct descendents.
In this case I looked at the HASH GROUP BY and TABLE ACCESS and got a difference of about 283 seconds. In fact I should have taken more notice of the other lines in the plan - comparing the HASH GROUP BY with the NESTED LOOP for a difference of about 16 seconds and assuming that the time in the TABLE ACCESS line was not to be trusted. (See http://jonathanlewis.wordpress.com/2007/04/26/heisenberg/ for a couple of comments on the timing issue).
So the grouping is responsible for relatively little of the excess time - most of the time goes into the nested loop.
I shall be using the Hints as advised, when we say we
have to "rewrite the query"
given the current context excluding the HINTS, what
exactly should I be
considering in terms of query rewrite, what
additional intelligence I can add to the
query in question so that CBO produces a different
plan.
The main consideration is what the query is supposed to report. Compare this with the way the optimizer is running the query and see if it makes sense.
When are talking about high intermediate rows
processing are we referring to this
section of the plan?;
4013304 TABLE ACCESS BY INDEX ROWID CI_FT
(cr=52997832 pr=11409 pw=0 time=140469508 us)
17717785 NESTED LOOPS (cr=49295470 pr=8987
pw=0 time=407554071 us)
13704480 NESTED LOOPS (cr=21818135 pr=7655
pw=0 time=287797921 us)
2782119 NESTED LOOPS OUTER (cr=3915432
pr=2950 pw=0 time=38953485 us)
2777066 TABLE ACCESS BY INDEX ROWID
CI_PER_CHAR (cr=1369669 pr=239 pw=0 time=23084761
us)
2777066 INDEX RANGE SCAN XM168P0 (cr=596156
pr=53 pw=0 time=7394319 us)(object id 98719)
13704480 TABLE ACCESS BY INDEX ROWID CI_SA
(cr=17902703 pr=4705 pw=0 time=163320548 us)
13704480 INDEX RANGE SCAN XM199S1
(cr=5688247 pr=104 pw=0 time=51063061 us)(object id
98973)
4013304 INDEX RANGE SCAN CM112S1 (cr=27477335
pr=1332 pw=0 time=124063022 us)(object id 116797)
Correct - one of the nested loops returns 2.78M rows - but as you run the next join you end up collecting 13.7M entires from the next index and table. That step is responsible for quite a lot of your work and time (as is the following step where you USE the 13.7M rows to probe the next index/table combination). If the optimizer had not grown the data set by merging the P view earlier on, the data sizes would be significantly smaller at that point.
Your inline view looks as if it is trying to turn rows into columns (the max(decode()) trick) - which is why I think it might be a good idea to stop Oracle from merging the view. So, as I suggested, look at the query withouth that bit of complexity and work out a sensible way to walk through the tables - bearing in mind the statistics below and the available indexes, and the amount of data your predicates identify at each stage.
Moreover tables have been analyzed:
CI_ACCT 243068
CI_ACCT_CHAR 222320
CI_ACCT_PER 242971
CI_FT 794510
CI_PER 13227
CI_PER_CHAR 42555
CI_PER_PHONE 18488
CI_SA 1082301
Parameters:
optimizer_features_enable string 10.2.0.2
optimizer_index_caching integer 100
optimizer_index_cost_adj integer 1
Unless you've been given strict instructions by a 3rd-part supplier, those settings for the optimizer_index_caching and optimizer_index_cost_adj are particularly bad - especially in 10g. With those settings, the optimizer is quite likely to choose stupid plans with excessive use of indexes - and pick the wrong index while doing it.
It's not appropriate to fiddle with system parameters to address one query - but at some stage you need to rethink your entire set of parameter settings to do things the 10g way. See this note from the Optimizer Group: http://www.oracle.com/technology/products/bi/db/10g/pdf/twp_bidw_optimizer_10gr2_0208.pdf
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
"The greatest enemy of knowledge is not ignorance,
it is the illusion of knowledge." Stephen Hawking. -
Huge long time direct path read temp, but pga size is enough, one block p3
Hi Gurus,
Can you please kindly provide some points on my below questions. thanks
my env
select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
OS: Linux 4 2.6.39-100.5.1.el5uek
session operation: update a partition which have 4 partitions and total 16G
session trace info:
the session keep at active status and waiting for below wait event for more than 70 hours, and os iostats and cpu are almost idle on most time.
WAIT #8: nam='direct path read temp' ela= 7615 file number=202 first dba=105072 block cnt=1 obj#=104719 tim=1344850223569499
WAIT #8: nam='direct path read temp' ela= 5989 file number=202 first dba=85264 block cnt=1 obj#=104719 tim=1344850392833257
WAIT #8: nam='direct path read temp' ela= 319 file number=202 first dba=85248 block cnt=1 obj#=104719 tim=1344850399563184
WAIT #8: nam='direct path read temp' ela= 358 file number=202 first dba=85232 block cnt=1 obj#=104719 tim=1344850406016899
WAIT #8: nam='direct path read temp' ela= 349 file number=202 first dba=85216 block cnt=1 obj#=104719 tim=1344850413023792
WAIT #8: nam='direct path read temp' ela= 7975 file number=202 first dba=85200 block cnt=1 obj#=104719 tim=1344850419495645
WAIT #8: nam='direct path read temp' ela= 331 file number=202 first dba=85184 block cnt=1 obj#=104719 tim=1344850426233450
WAIT #8: nam='direct path read temp' ela= 2641 file number=202 first dba=82880 block cnt=1 obj#=104719 tim=1344850432699800
pgastat:
NAME VALUE/1024/1024 UNIT
aggregate PGA target parameter 18432 bytes
aggregate PGA auto target 16523.1475 bytes
global memory bound 1024 bytes
total PGA inuse 75.7246094 bytes
total PGA allocated 162.411133 bytes
maximum PGA allocated 514.130859 bytes
total freeable PGA memory 64.625 bytes
PGA memory freed back to OS 40425.1875 bytes
total PGA used for auto workareas 2.75195313 bytes
maximum PGA used for auto workareas 270.407227 bytes
total PGA used for manual workareas 0 bytes
NAME VALUE/1024/1024 UNIT
maximum PGA used for manual workareas 24.5429688 bytes
bytes processed 110558.951 bytes
extra bytes read/written 15021.2559 bytes
Most operation in PGA via query on V$SQL_WORKAREA_ACTIVE
IDX maintainenance (sort)
My questions:
1. why 'direct path read temp' just read one block every time, my understanding is this event can read one block and multiple blocks at one read call, why it keep read one block in my session?
2. my pga size is big enough, why this operation can not be treated with in PGA memory, instead of read block from disk into temp tablespace?
Thanks for you inputs.
Roy951241 wrote:
since the session(which was from hard code application) is completed.First of all, you showed wait events from sql trace in the first post. Is the tracing was disabled in the latest execution?
>
I just generated the AWR for that period, as get long elapsed time SQL as following
Elapsed Time (s) Executions Elapsed Time per Exec (s) %Total %CPU %IO SQL Id
3,075.35 0 85.10 91.03 8.68 duhz2wtduz709
524.11 1 524.11 14.50 99.29 0.30 3cpa9fxny9j35
so I get execution plan as below for these two SQL,
select * from table(dbms_xplan.display_awr('&v_sql_id')); duhz2wtduz709
PLAN_TABLE_OUTPUT
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | UPDATE STATEMENT | | | | 4 (100)| |
| 1 | UPDATE | WORK_PAY_LINE | | | | |
| 2 | INDEX RANGE SCAN| WORK_PAY_LINE | 1 | 37 | 3 (0)| 00:00:01 |
Note
- automatic DOP: Computed Degree of Parallelism is 1 because of parallel thresholdI am not sure the why elapsed time in AWR is different with time in execution plan. Column "Time" in an execution plan is estimated time. In this execution plan Oracle expects to get 1 row, estimated time is 1 sec.
So, you need to check why estimated cardinality is such low, check statistics on the table WORK_PAY_LINE.
You update 10Gb from 16Gb table via Index Range Scan, it looks inefficient here by two reasons:
1. when a table updated via Index Range Scan optimized index maintenance is used. As a result some amount (significant in your case) of workareas is required. Required size depends on size and number of updated indexes and "global memory bound", 1Gb in your case.
2. if required table buffers will not be found in the cache it will be read from disk by single block reads. If you would use Full Table Scan then buffers for update most likely will be found in the cache because before it read by multiblock reads during Full Table Scan.
Figures from your AWR indicate, that only ~ 9% the session waited for I/O and 91% it worked and used CPU
Elapsed Time (s) Executions Elapsed Time per Exec (s) %Total %CPU %IO SQL Id
3,075.35 0 85.10 91.03 8.68 duhz2wtduz709 This amount of CPU time partially required for UPDATE 10Gb of data, partially for sorting during optimized index maintenance.
I would propose to use Table Full Scan here.
Also you can play around and create fake trigger on update, it will make impossible to use optimized index maintenance, usual index maintenance will be used. As a result you can check the same update with the same execution plan (with Index Range Scan) but without optimized index maintenance and "direct path .. temp" wait events.
Alexander Anokhin
http://alexanderanokhin.wordpress.com/ -
Hi All,
DB version is 10.2.0.4
An insert statement is running for almost 14 hours now. The wait event shows direct path read temp
SID EVENT WAIT_TIME SECONDS_IN_WAIT P1 P2
1264 direct path read temp -1 0 524 64626Read about this event, which says it might happen due to Parallel full table scan not using the index. But that is not happening here..
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | INSERT STATEMENT | | 1 | 512 | 941 (1)| 00:00:12 |
| 1 | COUNT | | | | | |
|* 2 | FILTER | | | | | |
| 3 | NESTED LOOPS | | 1 | 512 | 941 (1)| 00:00:12 |
| 4 | NESTED LOOPS | | 1 | 506 | 940 (1)| 00:00:12 |
| 5 | NESTED LOOPS | | 1 | 493 | 938 (1)| 00:00:12 |
| 6 | NESTED LOOPS | | 1 | 478 | 937 (1)| 00:00:12 |
| 7 | NESTED LOOPS | | 1 | 439 | 936 (1)| 00:00:12 |
| 8 | NESTED LOOPS | | 1 | 420 | 934 (1)| 00:00:12 |
| 9 | NESTED LOOPS | | 1 | 382 | 932 (1)| 00:00:12 |
| 10 | NESTED LOOPS | | 1 | 377 | 931 (1)| 00:00:12 |
| 11 | NESTED LOOPS | | 1 | 295 | 929 (1)| 00:00:12 |
| 12 | NESTED LOOPS | | 1 | 280 | 927 (1)| 00:00:12 |
| 13 | NESTED LOOPS | | 1 | 273 | 927 (1)| 00:00:12 |
| 14 | NESTED LOOPS | | 1 | 247 | 925 (1)| 00:00:12 |
| 15 | NESTED LOOPS | | 1 | 239 | 924 (1)| 00:00:12 |
| 16 | NESTED LOOPS | | 1 | 212 | 922 (1)| 00:00:12 |
| 17 | NESTED LOOPS | | 1 | 205 | 921 (1)| 00:00:12 |
| 18 | NESTED LOOPS | | 1 | 184 | 156 (1)| 00:00:02 |
| 19 | NESTED LOOPS | | 1 | 109 | 154 (1)| 00:00:02 |
| 20 | NESTED LOOPS | | 1 | 93 | 153 (1)| 00:00:02 |
|* 21 | HASH JOIN | | 4 | 284 | 145 (1)| 00:00:02 |
|* 22 | TABLE ACCESS BY INDEX ROWID | GL_JE_LINES | 65 | 2730 | 130 (0)| 00:00:02 |
| 23 | NESTED LOOPS | | 75 | 4500 | 140 (0)| 00:00:02 |
| 24 | MERGE JOIN CARTESIAN | | 1 | 18 | 10 (0)| 00:00:01 |
| 25 | TABLE ACCESS FULL | FND_PRODUCT_GROUPS | 1 | 2 | 2 (0)| 00:00:01 |
| 26 | BUFFER SORT | | 1 | 16 | 8 (0)| 00:00:01 |
|* 27 | TABLE ACCESS BY INDEX ROWID| GL_CODE_COMBINATIONS | 1 | 16 | 8 (0)| 00:00:01 |
|* 28 | INDEX RANGE SCAN | JSW_GL_CODE_COMB_SEG_IDX | 10 | | 2 (0)| 00:00:01 |
|* 29 | INDEX RANGE SCAN | GL_JE_LINES_N1 | 933 | | 6 (0)| 00:00:01 |
|* 30 | TABLE ACCESS FULL | GL_PERIODS | 5 | 55 | 4 (0)| 00:00:01 |
|* 31 | TABLE ACCESS BY INDEX ROWID | GL_JE_HEADERS | 1 | 22 | 2 (0)| 00:00:01 |
|* 32 | INDEX UNIQUE SCAN | GL_JE_HEADERS_U1 | 1 | | 1 (0)| 00:00:01 |
| 33 | TABLE ACCESS BY INDEX ROWID | GL_CODE_COMBINATIONS | 1 | 16 | 1 (0)| 00:00:01 |
|* 34 | INDEX UNIQUE SCAN | GL_CODE_COMBINATIONS_U1 | 1 | | 0 (0)| 00:00:01 |
|* 35 | TABLE ACCESS BY INDEX ROWID | GL_JE_BATCHES | 1 | 75 | 2 (0)| 00:00:01 |
|* 36 | INDEX UNIQUE SCAN | GL_JE_BATCHES_U1 | 1 | | 1 (0)| 00:00:01 |
|* 37 | TABLE ACCESS BY INDEX ROWID | MTL_TRANSACTION_ACCOUNTS | 1 | 21 | 765 (0)| 00:00:10 |
|* 38 | INDEX RANGE SCAN | MTL_TRANSACTION_ACCOUNTS_N3 | 4021 | | 28 (0)| 00:00:01 |
|* 39 | TABLE ACCESS BY INDEX ROWID | HR_ALL_ORGANIZATION_UNITS | 1 | 7 | 1 (0)| 00:00:01 |
|* 40 | INDEX UNIQUE SCAN | HR_ORGANIZATION_UNITS_PK | 1 | | 0 (0)| 00:00:01 |
|* 41 | TABLE ACCESS BY INDEX ROWID | HR_ORGANIZATION_INFORMATION | 1 | 27 | 2 (0)| 00:00:01 |
|* 42 | INDEX RANGE SCAN | HR_ORGANIZATION_INFORMATIO_FK2 | 1 | | 1 (0)| 00:00:01 |
| 43 | TABLE ACCESS BY INDEX ROWID | MTL_PARAMETERS | 1 | 8 | 1 (0)| 00:00:01 |
|* 44 | INDEX UNIQUE SCAN | MTL_PARAMETERS_U1 | 1 | | 0 (0)| 00:00:01 |
|* 45 | TABLE ACCESS BY INDEX ROWID | HR_ORGANIZATION_INFORMATION | 1 | 26 | 2 (0)| 00:00:01 |
|* 46 | INDEX RANGE SCAN | HR_ORGANIZATION_INFORMATIO_FK2 | 1 | | 1 (0)| 00:00:01 |
|* 47 | INDEX UNIQUE SCAN | HR_ALL_ORGANIZATION_UNTS_TL_PK | 1 | 7 | 0 (0)| 00:00:01 |
|* 48 | TABLE ACCESS BY INDEX ROWID | MTL_MATERIAL_TRANSACTIONS | 1 | 15 | 2 (0)| 00:00:01 |
|* 49 | INDEX UNIQUE SCAN | MTL_MATERIAL_TRANSACTIONS_U1 | 1 | | 1 (0)| 00:00:01 |
| 50 | TABLE ACCESS BY INDEX ROWID | MTL_SYSTEM_ITEMS_B | 1 | 82 | 2 (0)| 00:00:01 |
|* 51 | INDEX UNIQUE SCAN | MTL_SYSTEM_ITEMS_B_U1 | 1 | | 1 (0)| 00:00:01 |
|* 52 | INDEX FULL SCAN | GL_SETS_OF_BOOKS_U2 | 1 | 5 | 1 (0)| 00:00:01 |
|* 53 | TABLE ACCESS BY INDEX ROWID | RCV_TRANSACTIONS | 1 | 38 | 2 (0)| 00:00:01 |
|* 54 | INDEX UNIQUE SCAN | RCV_TRANSACTIONS_U1 | 1 | | 1 (0)| 00:00:01 |
|* 55 | TABLE ACCESS BY INDEX ROWID | PO_HEADERS_ALL | 1 | 19 | 2 (0)| 00:00:01 |
|* 56 | INDEX UNIQUE SCAN | PO_HEADERS_U1 | 1 | | 1 (0)| 00:00:01 |
| 57 | TABLE ACCESS BY INDEX ROWID | PO_VENDORS | 1 | 39 | 1 (0)| 00:00:01 |
|* 58 | INDEX UNIQUE SCAN | PO_VENDORS_U1 | 1 | | 0 (0)| 00:00:01 |
| 59 | TABLE ACCESS BY INDEX ROWID | PO_VENDOR_SITES_ALL | 1 | 15 | 1 (0)| 00:00:01 |
|* 60 | INDEX UNIQUE SCAN | PO_VENDOR_SITES_U1 | 1 | | 0 (0)| 00:00:01 |
| 61 | TABLE ACCESS BY INDEX ROWID | RCV_SHIPMENT_HEADERS | 1 | 13 | 2 (0)| 00:00:01 |
|* 62 | INDEX UNIQUE SCAN | RCV_SHIPMENT_HEADERS_U1 | 1 | | 1 (0)| 00:00:01 |
|* 63 | INDEX UNIQUE SCAN | RCV_SHIPMENT_LINES_U1 | 1 | 6 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------------------------------------------The PGA size is 5gb. What is the cause of this wait event?
baskar.lHi,
How do i resolve this..?
Read from the document Optimizer Selects the Merge Join Cartesian Despite the Hints (Doc ID 457058.1)
| 24 | MERGE JOIN CARTESIAN | | 1 | 18 | 10 (0)| 00:00:01 |
| 25 | TABLE ACCESS FULL | FND_PRODUCT_GROUPS | 1 | 2 | 2 (0)| 00:00:01 |
| 26 | BUFFER SORT | | 1 | 16 | 8 (0)| 00:00:01 |
|* 27 | TABLE ACCESS BY INDEX ROWID| GL_CODE_COMBINATIONS | 1 | 16 | 8 (0)| 00:00:01 |
|* 28 | INDEX RANGE SCAN | JSW_GL_CODE_COMB_SEG_IDX | 10 | | 2 (0)| 00:00:01 |Have set
SQL> alter session set "_optimizer_mjc_enabled"=false ;
|* 21 | HASH JOIN | | 4 | 284 | 139 (1)| 00:00:02 |
|* 22 | TABLE ACCESS BY INDEX ROWID | GL_JE_LINES | 65 | 2730 | 124 (0)| 00:00:02 |
| 23 | NESTED LOOPS | | 75 | 4500 | 134 (0)| 00:00:02 |
| 24 | NESTED LOOPS | | 1 | 18 | 10 (0)| 00:00:01 |
| 25 | TABLE ACCESS FULL | FND_PRODUCT_GROUPS | 1 | 2 | 2 (0)| 00:00:01 |
|* 26 | TABLE ACCESS BY INDEX ROWID| GL_CODE_COMBINATIONS | 1 | 16 | 8 (0)| 00:00:01 |
|* 27 | INDEX RANGE SCAN | JSW_GL_CODE_COMB_SEG_IDX | 10 | | 2 (0)| 00:00:01 |thanks,
baskar.l -
Query occasionally causes table scans (db file sequential read)
Dear all,
we periodically issue a query on a huge table via an oracle job.
Whenever I invoke the query manually, the response time is good. When I start the periodic job, initially the response times are good as well. After some days, however, the query suddenly takes almost forever.
My vague guess is that for some reason the query suddenly changes the execution plan from using the primary key index to a full table scan (or huge index range scan). Maybe because of some problems with the primary key index (fragmentation? Other?).
- Could it be the case that the execution plan for a query changes (automatically) like this? For what reasons?
- Do you have any hints where to look for further information for analysis? (logs, special event types, ...)?
- Of course, the query was designed having involved indexes in mind. Also, I studied the execution plan and did not find hints for problematic table/range scans.
- It is not a lock contention problem
- When the query "takes forever", there is a "db file sequential read" event in v$session_event for the query with an ever increasing wait time. That's why I guess a (unreasonable) table scan is happening.
Some charachteristics of the table in question:
- ~ 30 Mio rows
- There are only insertions to the table, as well as updates on a single, indexed field. No deletes.
- There is an integer primary key field with an B-tree index.
Charachteristics of the query:
The main structure of the query is very simple and as follows: I select a range of about 100 rows via primary key "id", like:
Select * from TheTable where id>11222300 and id <= 11222400
There are several joins with rather small tables, which make the overall query more complicated.
However, the few (100) rows of the huge table in question should always be fetched using the primary key index, shouldn't it?
Please let me know if some relevant information about the problem is missing.
Thanks!
Best regards,
Nang.user2560749 wrote:
Dear all,
we periodically issue a query on a huge table via an oracle job.
Whenever I invoke the query manually, the response time is good. When I start the periodic job, initially the response times are good as well. After some days, however, the query suddenly takes almost forever.
My vague guess is that for some reason the query suddenly changes the execution plan from using the primary key index to a full table scan (or huge index range scan). Maybe because of some problems with the primary key index (fragmentation? Other?).
- Could it be the case that the execution plan for a query changes (automatically) like this? For what reasons?Yes possible, One reason is stats of the table has been changed i.e somebody issued dbms_stats. If you are worried about execution plan getting changed then two option 1) Lock the stats 2) Use hint in the query.
- Do you have any hints where to look for further information for analysis? (logs, special event types, ...)?Have a Ora-10053 trace enabled whenever query plan changes and analysis it.
- Of course, the query was designed having involved indexes in mind. Also, I studied the execution plan and did not find hints for problematic table/range scans.
- It is not a lock contention problem
- When the query "takes forever", there is a "db file sequential read" event in v$session_event for the query with an ever increasing wait time. That's why I guess a (unreasonable) table scan is happening.
If it db file sequential read then i see two things 1) It is doing index range scan(Not table full scan) or 2) It is scanning undo tablespaces.
Some charachteristics of the table in question:
- ~ 30 Mio rows
- There are only insertions to the table, as well as updates on a single, indexed field. No deletes.
- There is an integer primary key field with an B-tree index.
Charachteristics of the query:
The main structure of the query is very simple and as follows: I select a range of about 100 rows via primary key "id", like:
Select * from TheTable where id>11222300 and id <= 11222400
There are several joins with rather small tables, which make the overall query more complicated.
However, the few (100) rows of the huge table in question should always be fetched using the primary key index, shouldn't it?
Yes theoreitically it should practically we can only say by looking at run time explain plan(through 10053,10046 trace).
Please let me know if some relevant information about the problem is missing.
Thanks!
Best regards,
Nang.I am still not sure in which direction you are looking for solution.
Is your query performing bad once in a fortnight and next day it is all same again.
I suggest to
1) Check if the data is scanning undo tablespace. I see you mentioned there is lot of inserts, could be that Oracle would be scanning undo tablespace because of delayed clean out.
2) Check if that particular day the number of records are high compared to other day.
Or once it starts performing bad then for next couple of days there is no change in response time.
1) Check if explain plan has been changed?
And what action you take to bring back the response time to normal?
Regards
Anurag -
Tables-Primary Key-Sequential read
Hi Folks,
Out of the following which imporves performace?
1.Using all the primary keys of a table in the where clause of a select statement?
2.Using any one or two (not all) primary keys of a table in the where clause of a select statement?
Let me the know the same in the case of using an Secondary index.
3.If we follow the second one,then it will go for a sequential read,how this sequential read mars the performance?
4.How creating an index will affect the database as BASIS guys are not in favour to creating an index.
Thanks,
K.Kiran.1.Using all the primary keys of a table in the where clause of a select statement?
2.Using any one or two (not all) primary keys of a table in the where clause of a select statement?
Out of the above 2 first one will give more performance. Coming to primary key or Secondary indexses, anything.. it gives better performance if you give the key fileds in the order of DB declaration.
I mean you are specifying some fields of primary key.. but not in the order .. i mean u have specified key1, key3, key4. It will give less performance than specifying only key1 and key2.
in secondary indexes if you are not specifying all key completely that will take the key up to the order matches. i mean in key1, key3, key4 case.. it will consider only Key1.
In Key1, Key2 case it will consider both.
3.If we follow the second one,then it will go for a sequential read,how this sequential read mars the performance?
4.How creating an index will affect the database as BASIS guys are not in favour to creating an index.
Creating an secondary index will save the table contents in the format of starting with index fields in the DB. So number of indexes on the same table will need to craete more views in database. So leads to poor DB performance. i mean more space unnecesarily for a single table. That's why they will create indexes only for very frequently used fields on tables. -
Optimize long execution time due to 'db file sequential read'
Hi to all,
I have got a query that takes long execution time. Most of the time is due to 'db file sequential read'. The query is:
SELECT * FROM Table_Name
WHERE col1 = :some_value
AND col2 BETWEEN :some_range_about_2_Million
| Id | Operation | Name | Rows | Bytes | Cost |
| 0 | SELECT STATEMENT | | 21 | 504 | 26125 |
| 1 | TABLE ACCESS BY INDEX ROWID| Table_Name | 21 | 504 | 26125 |
| 2 | INDEX RANGE SCAN | Index Name | 1705K| | 4100 |
The table is not partitioned having around 0.2 billion records. Record set for column 'col1' is around 1700K.
Another index is available for the col2 and col3 is not getting used.
Any suggestions to optimize it..
Regards.Perhaps a combined index (col2, col1) would work...or try "parallel" hint.
:p -
제품 : ORACLE SERVER
작성날짜 : 1998-11-27
매우 많은 양의 데이타를 빠른 시간 내에 load하고자하는 경우 direct path load를
사용할 수 있다. 여기에서 이러한 direct path load의 자세한 개념 및 사용방법,
사용 시 고려해야 할 점 등을 설명한다.
1. conventional path load
일반적인 sql*loader를 이용한 방법은 존재하는 table에 datafile 내의 data를
SQL의 INSERT command를 이용하여 insert시킨다. 이렇게 SQL command를
이용하기 때문에 각각의 데이타를 위한 insert command가 생성되어 parsing되는
과정이 필요하며, 먼저 bind array buffer (data block buffer) 내에 insert되는
데이타를 입력시킨 후 이것을 disk에 write하게 된다.
conventional path load를 사용하여야 하는 경우는 다음과 같다.
--- load 중에 table을 index를 이용하여 access하여야 하는 경우
direct load중에는 index가 'direct load state'가 되어 사용이 불가능하다.
--- load 중에 index를 사용하지 않고 table을 update나 insert등을 수행해야
하는 경우
direct load 중에는 table에 exclusive write(X) lock을 건다.
--- SQL*NET을 통해 load를 수행해야 하는 경우
--- clustered table에 load하여야 하는 경우
--- index가 걸려 있는 큰 table에 적은 수의 데이타를 load하고자 할 때
--- referential이나 check integrity가 정의되어 있는 큰 table에
load하고자 할 때
--- data field에 SQL function을 사용하여 load하고자 할 때
2. direct path load의 수행 원리
Direct Path Loads는 다음과 같은 특징들로 인하여 매우 많은 양의 데이타를
빠른 시간에 load하고자 할 때 이용하는 것이 바람직하다.
(1) SQL INSERT 문장을 generate하여 수행하지 않는다.
(2) memory 내의 bind array buffer를 이용하지 않고 database block의
format과 같은 data
block을 memory에 만들어 데이타를 넣은 후 그대로 disk에 write한다.
memory 내의 block buffer와 disk의 block은 그 format이 다르다.
(3) load 시작 시에 table에 lock을 걸고 load가 끝나면 release시킨다.
(4) table의 HWM (High Water Mark) 윗 부분의 block에 data를 load한다.
HWM는 table에 data가 insert됨에 따라 계속 늘어나고 truncate 외에는
줄어들게 하지 못한다.
그러므로, 항상 완전히 빈 새로운 block을 할당받아 data를 입력시키게 된다.
(5) instance failure가 발생하여도 redo log file을 필요로 하지 않는다.
(6) UNDO information을 발생시키지 않는다.
즉 rollback segment를 사용하지 않는다.
(7) OS에서 asynchronous I/O가 가능하다면, 복수개의 buffer에 의해서 동시에
data를 읽어서 buffer에 write하면서 buffer에서 disk로 write할 수 있다.
(8) parallel option을 이용하면 더욱 성능을 향상시킬 수 있다.
3. direct path load의 사용방법 및 options
direct path load를 사용하기 위한 view들은 다음 script에 포함어 있으며,
미리 sys user로 수행되어야 한다. 단 이 script는 catalog.sql에 포함되어 있어,
db 구성 시에 이미 수행되어진다.
@$ORACLE_HOME/rdbms/admin/catldr.sql
direct path load를 사용하기 위해서는 일반적인 sqlload 명령문에 DIRECT=TRUE를
포함시키기만 하면 된다. 다음과 같이 기술하면 된다.
sqlload username/password control=loadtest.ctl direct=true
이 direct path load를 사용 시에 고려할 만한 추가적인 option 및 control file
내에 기술 가능한 clause들을 살펴본다.
(1) ROWS = n
conventional path load에서 rows는 default가 64이며, rows에 지정된 갯수
만큼의 row가 load되면 commit이 발생한다. 이와 비슷하게 direct load
path에서는 rows option을 이용하여 data save를 이루며, data save가 발생하면
data는 기존 table에 포함되어 입력된 data를 잃지 않게 된다.
단 이 때 direct path load는 모든 data가 load된 다음에야 index가
구성되므로 data save가 발생하여도 index는 여전히 direct load state로
사용하지 못하게 된다.
direct path load에서 이 rows의 default값은 unlimited이며, 지정된 값이
database block을 채우지 못하면 block을 완전히 채우는 값으로 올림하여,
partial block이 생성되지 않도록 한다.
(2) PIECED clause
control file내에 column_spec datatype_spec PIECED 순으로 기술하는
것으로서 direct path load에만 유효하다. LONG type과 같이 하나의 data가
maximum buffer size보다 큰 경우 하나의 data를 여러번에 나누어 load하는
것이다. 이 option은 table의 맨 마지막 field
하나에만 적용가능하며, index column인 경우에는 사용할 수 없다.
그리고 load도중 data에 문제가 있는 경우 현재 load되는 data의 잘린 부분만
bad file에 기록되게 된다. 왜냐하면 이전 조각은 이미 datafile에 기록되어
buffer에는 남아있지 않기 때문이다.
(3) READBUFFERS = n (default is 4)
만약 매우 큰 data가 마지막 field가 아니거나 index의 한 부분인 경우
PIECED option을 사용할 수 없다. 이러한 경우 buffer size를 증가시켜야
하는데 이것은 readbuffers option을 이용하면 된다. default buffer갯수는
4개이며, 만약 data load중 ORA-2374(No more slots for read buffer
queue) message가 나타나면, buffer갯수가 부족한 것이므로 늘려주도록 한다.
단 일반적으로는 이 option을 이용하여 값을 늘린다하더라도 system
overhead만 증가하고 performance의 향상은 기대하기 어렵다.
4. direct path load에서의 index 처리
direct path load에서 인덱스를 생성하는 절차는 다음과 같다.
(1) data가 table에 load된다.
(2) load된 data의 key 부분이 temporary segment에 copy되어 sort된다.
(3) 기존에 존재하던 index와 (2)에 의해서 정렬된 key가 merge된다.
(4) (3)에 의해서 새로운 index가 만들어진다.
기존에 존재하던 index와 temporary segment, 그리고 새로 만들어지는 index가
merge가 완전히 끝날 때까지 모두 존재한다.
(5) old index와 temporary segment는 지워진다.
이와 같은 절차에 반해 conventional path load는 data가 insert될 때마다 한
row 씩 index에 첨가된다. 그러므로 temporary storage space는 필요하지 않지만
direct path load에 비해 index 생성 시간도 느리고, index tree의 balancing도
떨어지게 된다.
index생성 시 필요한 temporary space는 다음과 같은 공식에 의해 예측되어질 수
있다.
1.3 * key_storage
key_storage = (number_of_rows) * (10 + sum_of_column_sizes +
number_of_columns)
여기에서 1.3은 평균적으로 sort 시에 추가적으로 필요한 space를 위한 값이며,
전체 data가 완전히 순서가 거꾸로 된 경우에는 2, 전체가 미리 정렬된 경우라면
1을 적용하면 된다.
--- SINGLEROW clause
이와 같이 direct path load에서 index 생성 시 space를 많이 차지하는 문제점
때문에 resource가 부족한 경우에는 SINGLEROW option을 사용할 수 있다.
이 option은 controlfile 내에 다음과 같은 형태로 기술하며, direct path
load에만 사용 가능하다.
into tables table_name [sorted indexes...] singlerow
이 option을 사용하면 전체 data가 load된 뒤에 index가 구성되는 것이 아니라
data가 load됨에 따라 data 각각이 바로 index에 추가된다.
이 option은 기존에 미리 index가 존재하는 경우 index를 생성하는 동안
merge를 위해 space를 추가적으로 필요로 하는 것을 막고자 하는 것이므로
INSERT 시에는 사용하지 않고, APPEND시에만 사용하도록 하고 있다.
실제 새로 load할 data 보다 기존 table이 20배 이상 클 때 사용하도록 권하고
있다.
direct path load는 rollback information을 기록하지 않지만, 이 singlerow
option을 사용하면 insert되는 index에 대해 undo 정보를 rollback segment에
기록하게 된다.
그러나, 중간에 instance failure가 발생하면 data는 data save까지는 보존
되지만 index는 여전히 direct load state로 사용할 수 없게 된다.
--- Direct Load State
만약 direct path load가 성공적으로 끝나지 않으면 index는 direct load
state로 된다.
이 index를 통해 조회하고자 하면 다음과 같은 오류가 발생한다.
ORA-01502 : index 'SCOTT.DEPT_PK' is in direct load state.
index가 direct load state로 되는 원인을 구체적으로 살펴보면 다음과 같다.
(1) index가 생성되는 과정에서 space가 부족한 경우
(2) SORTED INDEXES clause가 사용되었으나, 실제 data는 정렬되어 있지 않은
경우
이러한 경우 data는 모두 load가 되고, index만이 direct load state로 된다.
(3) index 생성 도중 instance failure가 발생한 경우
(4) unique index가 지정되어 있는 컬럼에 중복된 data가 load되는 경우
특정 index가 direct load state인지를 확인하는 방법은 다음과 같다.
select index_name, status
from user_indexes
where table_name = TABLE_NAME';
만약 index가 direct load state로 나타나면 그 index는 drop하고 재생성
하여야만 사용할 수 있다. 단, direct load 중에는 모든 index가 direct
load state로 되었다가 load가 성공적으로 끝나면 자동으로 valid로 변경된다.
--- Pre-sorting (SORTED INDEX)
direct load 시 index구성을 위해서 정렬하는 시간을 줄이기 위해 미리 index
column에 대해서 data를 정렬하여 load시킬 수 있다. 이 때 control file 내에
SORTED INDEXES option을 다음과 같이 정의한다.
이 option은 direct path load 시에만 유효하며, 복수 개의 index에 대해서
지정가능하다.
into table table_name SORTED INDEXES (index_names_with_blank)
만약, 기존의 index가 이미 존재한다면, 새로운 key를 일시적으로 저장할 만큼
의 temporary storage가 필요하며, 기존 index가 없는 경우였다면, 이러한
temporary space도 필요하지 않다.
이와 같이 direct path load 시에 index 구성 시에는 기존 데이타가 있는 table에
load하는 경우 space도 추가적으로 들고, load가 완전히 성공적으로 끝나지 않으면
index를 재생성하여야 하므로, 일반적으로 direct path load 전에 미리 table의
index를 제거한 후 load가 모두 끝난 후 재생성하도록 한다.
5. Recovery
direct load는 기존 segment중간에 data를 insert하는 것이 아니라 완전히
새로운 block을 할당받아 정확히 write가 끝난 다음 해당 segment에 포함되기
때문에 instance failure시에는 redo log정보를 필요로 하지 않는다. 그러나
default로 direct load는 redo log에 입력되는 data를 기록하는데 이것은 media
recovery를 위한 것이다. 그러므로 archive log mode가 아니면 direct load에
생성된 redo log 정보는 불필요하게 되므로 NOARCHIVELOG mode시에는 항상
control file내에 UNRECOVERABLE이라는 option을 사용하여 redo log에 redo entry를 기록하지 않도록 한다.
data가 redo log 정보 없이 instance failure시에 data save까지는 보호되는데
반해 index는 무조건 direct load state가 되어 재생성하여야 한다. 그리고 data save이후의 load하고자 하는 table에 할당되었던 extent는 load된 data가
user에게 보여지지는 않지만 extent가 free space로 release되지는 않는다.
6. Integrity Constraints & Triggers
direct path load중 not null, unique, primary key constraint는 enable
상태로 존재한다. not null은 insert시에 check되고 unique는 load후 index를
구성하는 시점에 check된다.
그러나 check constraint와 referential constraint는 load가 시작되면서
disable상태로 된다. 전체 데이타가 load되고 난 후 이렇게 disable된
constraints를 enable시키려면 control file내에 REENABLE이라는 option을
지정하여야 한다. 이 reenable option은 각 constraint마다 지정할 수는 없으며
control file에 한번 지정하면 전체 integrity/check constraint에 영향을
미치게 된다. 만약 reenable되는 과정에서 constraint를 위배하는 data가
발견되면 해당 constraint는 enable되지 못하고 disabled status로 남게 되며,
이렇게 위배된 data를 확인하기 위해서는 reenable clause에 exceptions option을 다음과 같이 추가하면 된다.
reenable [exceptions table_name]
이 때 table_name은 $ORACLE_HOME/rdbms/admin/utlexcpt.sql을 다른
directory로copy하여 table이름을 exceptions가 아닌 다른 이름으로 만들어 수행시키면 된다.
insert trigger도 integrity/check constraint와 같이 direct load가 시작하는
시점에 disable되며, load가 끝나면 자동으로 enable된다. 단 enable되고 나서도
load에 의해 입력된 data에 대해 trigger가 fire되지는 않는다. -
Getting wait event "direct path write temp" during query execution
Hi All,
While executing one query in database, it is taking longer time and failing with error "ORA-01652: unable to extend temp segment by 1280 in tablespace PSTEMP".
I have increaesd the Temp tablespace size also till 96GB, Database size is 120GB.
I have upgraded the database from 10.2.0.3 to 11.2.0.3 version last month.
same query is running fine in other databases on same version.
It is giving me "Direct write temp path" wait event.
server load is also normal.
I have increased pga_aggregate_target upto 512MB but it has not solved my problem
Can you please help me out to solve this issue.Hi Nicolay,
Please find below output from that query :
SQL>
SELECT DBMS_SQLTUNE.report_sql_monitor(
sql_id => '(*******',
type => 'TEXT',
report_level => 'ALL') AS report
FROM dual;SQL> 2 3 4 5
SQL Monitoring Report
SQL Text
SELECT ASGN.TRANSACTIONID ,ASGN.UPA_CLIENT_ID FROM PS_UPA_CM_PRE_ASGN ASGN ,PS_UPA_CLIENT_TBL CL ,PS_UPA_CM_ADMIN_WL WL ,PSXLATITEM XCT ,PSXLATITEM XCS ,PS_PWC_INDUSTR_TBL IND ,PS_PWC_SUBIND_TBL SCT ,PS_UPA_FIN_REG_TBL REG ,PS_UPA_CM_MKT_VW1 MKT WHERE ASGN.UPA_CLIENT_ID = CL.UPA_CLIENT_ID AND CL.UPA_CM_GRP_ID = ' ' AND ASGN.UPA_CM_ADMIN_ACT = 'RCD' AND ASGN.UPA_CM_CLT_ROLENBR = WL.UPA_CM_CLT_ROLENBR AND ASGN.UPA_CM_ROLENBR_SEQ = WL.UPA_CM_ROLENBR_SEQ AND WL.UPA_CM_WL_STATUS = 'A' AND
WL.UPA_CM_ADMIN_ACT = 'RCD' AND CL.EFFDT = ( SELECT MAX(CL1.EFFDT) FROM PS_UPA_CLIENT_TBL CL1 WHERE CL1.UPA_CLIENT_ID = CL.UPA_CLIENT_ID AND CL1.EFFDT <= SYSDATE) AND CL.EFF_STATUS = 'A' AND CL.UPA_MONTH_DAY <> ' ' AND CL.UPA_CLIENT_TYPE <> ' ' AND CL.UPA_CLIENT_SEGMENT <> ' ' AND CL.PWC_INDUSTRY <> ' ' AND CL.PWC_SUB_INDUSTRY <> ' ' AND CL.UPA_FIN_REGION <> ' ' AND CL.UPA_STRAT_MKT <> ' ' AND CL.UPA_CLT_PRIORITIZ <> ' ' /*Harieash - Aadded as part of PR support IR 43024 */ AND XCT.FIELDNAME =
'UPA_CLIENT_TYPE' AND XCT.FIELDVALUE = CL.UPA_CLIENT_TYPE AND XCT.EFFDT = ( SELECT MAX(XCT1.EFFDT) FROM PSXLATITEM XCT1 WHERE XCT1.FIELDNAME = XCT.FIELDNAME AND XCT1.FIELDVALUE = XCT.FIELDVALUE AND XCT1.EFFDT <= SYSDATE) AND XCT.EFF_STATUS = 'A' AND XCS.FIELDNAME = 'UPA_CLIENT_SEGMENT' AND XCS.FIELDVALUE = CL.UPA_CLIENT_SEGMENT AND XCS.EFFDT = ( SELECT MAX(XCS1.EFFDT) FROM PSXLATITEM XCS1 WHERE XCS1.FIELDNAME = XCS.FIELDNAME AND XCS1.FIELDVALUE = XCS.FIELDVALUE AND XCS1.EFFDT <= SYSDATE) AND
XCS.EFF_STATUS = 'A' AND IND.SETID = 'USA00' AND CL.PWC_INDUSTRY = IND.PWC_INDUSTRY AND IND.EFFDT = ( SELECT MAX(IND1.EFFDT) FROM PS_PWC_INDUSTR_TBL IND1 WHERE IND1.SETID = IND.SETID AND IND1.PWC_INDUSTRY = IND.PWC_INDUSTRY AND IND1.EFFDT <= SYSDATE) AND IND.EFF_STATUS = 'A' AND SCT.SETID = 'USA00' AND CL.PWC_SUB_INDUSTRY = SCT.PWC_SUB_INDUSTRY AND SCT.EFFDT = ( SELECT MAX(SCT1.EFFDT) FROM PS_PWC_SUBIND_TBL SCT1 WHERE SCT1.SETID = SCT.SETID AND SCT1.PWC_SUB_INDUSTRY = SCT.PWC_SUB_INDUSTRY AND
SCT1.EFFDT <= SYSDATE) AND SCT.EFF_STATUS = 'A' AND REG.SETID = 'USA00' AND CL.UPA_FIN_REGION = REG.UPA_FIN_REGION AND REG.EFFDT = ( SELECT MAX(REG1.EFFDT) FROM PS_UPA_FIN_REG_TBL REG1 WHERE REG1.SETID = 'USA00' AND REG1.UPA_FIN_REGION = REG.UPA_FIN_REGION AND REG1.EFFDT <= SYSDATE) AND REG.EFF_STATUS = 'A' AND CL.UPA_STRAT_MKT = MKT.UPA_STRAT_MKT
Global Information
Status : EXECUTING
Instance ID : 1
Session : *******
SQL ID : *******
SQL Execution ID : *********
Execution Started : 11/12/2012 04:31:25
First Refresh Time : 11/12/2012 04:31:33
Last Refresh Time : 11/12/2012 04:31:55
Duration : 31s
Module/Action : ***** (TNS V1-V3)/-
Service : SYS$USERS
Program : ******* (TNS V1-V3)
Global Stats
=========================================================
| Elapsed | Cpu | IO | Buffer | Write | Write |
| Time(s) | Time(s) | Waits(s) | Gets | Reqs | Bytes |
=========================================================
| 33 | 25 | 7.30 | 162 | 4755 | 557MB |
=========================================================
SQL Plan Monitoring Details (Plan Hash Value=2177602723)
========================================================================================================================================================================================================
| Id | Operation | Name | Rows | Cost | Time | Start | Execs | Rows | Write | Write | Mem | Temp | Activity | Activity Detail |
| | | | (Estim) | | Active(s) | Active | | (Actual) | Reqs | Bytes | | | (%) | (# samples) |
========================================================================================================================================================================================================
| 0 | SELECT STATEMENT | | | | | | 1 | | | | | | | |
| 1 | NESTED LOOPS | | | | | | 1 | | | | | | | |
| 2 | NESTED LOOPS | | 1 | 491 | | | 1 | | | | | | | |
| -> 3 | HASH JOIN | | 120 | 130 | 31 | +1 | 1 | 0 | 4011 | 470MB | 95M | 598M | 80.65 | Cpu (19) |
| | | | | | | | | | | | | | | direct path write temp (6) |
| -> 4 | MERGE JOIN CARTESIAN | | 120 | 61 | 23 | +8 | 1 | 13M | | | | | | |
| -> 5 | MERGE JOIN CARTESIAN | | 1 | 38 | 23 | +8 | 1 | 1870 | | | | | | |
| -> 6 | MERGE JOIN CARTESIAN | | 1 | 37 | 23 | +8 | 1 | 70 | | | | | | |
| -> 7 | MERGE JOIN CARTESIAN | | 1 | 35 | 23 | +8 | 1 | 12 | | | | | | |
| 8 | MERGE JOIN CARTESIAN | | 1 | 33 | 21 | +8 | 1 | 2 | | | | | | |
| 9 | MERGE JOIN CARTESIAN | | 1 | 31 | 1 | +8 | 1 | 1 | | | | | | |
| 10 | VIEW | PS_UPA_CM_MKT_VW1 | 1 | 29 | 1 | +8 | 1 | 1 | | | | | | |
| 11 | SORT UNIQUE | | 1 | 28 | 1 | +8 | 1 | 1 | | | | | | |
| 12 | TABLE ACCESS BY INDEX ROWID | PS_UPA_ST_MKT_TBL | 10 | 2 | 1 | +8 | 1 | 43 | | | | | | |
| 13 | INDEX SKIP SCAN | PS0UPA_ST_MKT_TBL | 10 | 1 | 1 | +8 | 1 | 43 | | | | | | |
| 14 | SORT AGGREGATE | | 1 | | 1 | +8 | 33 | 33 | | | | | | |
| 15 | INDEX SKIP SCAN | PS0UPA_ST_MKT_TBL | 2 | 1 | 1 | +8 | 33 | 50 | | | | | | |
| 16 | BUFFER SORT | | 1 | 31 | 1 | +8 | 1 | 1 | | | | | | |
| 17 | TABLE ACCESS BY INDEX ROWID | PSXLATITEM | 1 | 2 | 1 | +8 | 1 | 14 | | | | | | |
| 18 | INDEX RANGE SCAN | PS_PSXLATITEM | 1 | 1 | 1 | +8 | 1 | 14 | | | | | | |
| 19 | SORT AGGREGATE | | 1 | | 1 | +8 | 14 | 14 | | | | | | |
| 20 | INDEX RANGE SCAN | PS_PSXLATITEM | 1 | 1 | 1 | +8 | 14 | 14 | | | | | | |
| 21 | BUFFER SORT | | 1 | 31 | 21 | +8 | 1 | 2 | | | | | | |
| 22 | TABLE ACCESS BY INDEX ROWID | PSXLATITEM | 1 | 2 | 1 | +8 | 1 | 2 | | | | | | |
| 23 | INDEX RANGE SCAN | PS_PSXLATITEM | 1 | 1 | 1 | +8 | 1 | 2 | | | | | | |
| 24 | SORT AGGREGATE | | 1 | | 1 | +8 | 2 | 2 | | | | | | |
| 25 | INDEX RANGE SCAN | PS_PSXLATITEM | 1 | 1 | 1 | +8 | 2 | 2 | | | | | | |
| -> 26 | BUFFER SORT | | 3 | 33 | 23 | +8 | 2 | 12 | | | | | | |
| 27 | TABLE ACCESS BY INDEX ROWID | PS_PWC_INDUSTR_TBL | 3 | 2 | 1 | +8 | 1 | 10 | | | | | | |
| 28 | INDEX SKIP SCAN | PS0PWC_INDUSTR_TBL | 6 | 1 | 1 | +8 | 1 | 26 | | | | | | |
| 29 | SORT AGGREGATE | | 1 | | 1 | +8 | 26 | 26 | | | | | | |
| 30 | FIRST ROW | | 1 | 1 | 1 | +8 | 26 | 26 | | | | | | |
| -> 31 | INDEX RANGE SCAN (MIN/MAX) | PS_PWC_INDUSTR_TBL | 1 | 1 | 23 | +8 | 26 | 26 | | | | | | |
| -> 32 | BUFFER SORT | | 3 | 35 | 23 | +8 | 12 | 70 | | | | | | |
| 33 | TABLE ACCESS BY INDEX ROWID | PS_UPA_FIN_REG_TBL | 3 | 2 | 1 | +8 | 1 | 6 | | | | | | |
| 34 | INDEX SKIP SCAN | PS0UPA_FIN_REG_TBL | 6 | 1 | 1 | +8 | 1 | 12 | | | | | | |
| 35 | SORT AGGREGATE | | 1 | | 1 | +8 | 12 | 12 | | | | | | |
| 36 | FIRST ROW | | 1 | 1 | 1 | +8 | 12 | 12 | | | | | | |
| -> 37 | INDEX RANGE SCAN (MIN/MAX) | PS_UPA_FIN_REG_TBL | 1 | 1 | 23 | +8 | 12 | 12 | | | | | | |
| -> 38 | BUFFER SORT | | 14 | 36 | 23 | +8 | 70 | 1870 | | | | | | |
| 39 | INDEX RANGE SCAN | PSAPWC_SUBIND_TBL | 14 | 1 | 1 | +8 | 1 | 27 | | | | | | |
| 40 | SORT AGGREGATE | | 1 | | 1 | +8 | 184 | 184 | | | | | | |
| 41 | FIRST ROW | | 1 | 2 | 1 | +8 | 184 | 184 | | | | | | |
| -> 42 | INDEX RANGE SCAN (MIN/MAX) | PS_PWC_SUBIND_TBL | 1 | 2 | 23 | +8 | 184 | 184 | | | | | | |
| 43 | BUFFER SORT | | 794 | 60 | 29 | +2 | 1870 | 13M | | | 306K | | 19.35 | Cpu (6) |
| 44 | TABLE ACCESS FULL | PS_UPA_CM_ADMIN_WL | 794 | 23 | 1 | +8 | 1 | 7052 | | | | | | |
| 45 | TABLE ACCESS FULL | PS_UPA_CM_PRE_ASGN | 3536 | 69 | | | | | | | | | | |
| 46 | INDEX RANGE SCAN | PSDUPA_CLIENT_TBL | 1 | 2 | | | | | | | | | | |
| 47 | SORT AGGREGATE | | 1 | | | | | | | | | | | |
| 48 | FIRST ROW | | 1 | 3 | | | | | | | | | | |
| 49 | INDEX RANGE SCAN (MIN/MAX) | PS_UPA_CLIENT_TBL | 1 | 3 | | | | | | | | | | |
| 50 | TABLE ACCESS BY INDEX ROWID | PS_UPA_CLIENT_TBL | 1 | 3 | | | | | | | | | | |
========================================================================================================================================================================================================
SQL>
spool offSQL> -
Wrong cardinality estimate for range scan
select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE 11.2.0.2.0 Production
TNS for Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - ProductionSQL : select * from GC_FULFILLMENT_ITEMS where MARKETPLACE_ID=:b1 and GC_FULFILLMENT_STATUS_ID=:b2;
Plan
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 474K| 99M| 102 (85)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| GC_FULFILLMENT_ITEMS | 474K| 99M| 102 (85)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_GCFI_GCFS_ID_SDOC_MKTPLID | 474K| | 91 (95)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("GC_FULFILLMENT_STATUS_ID"=TO_NUMBER(:B2) AND "MARKETPLACE_ID"=TO_NUMBER(:B1))
filter("MARKETPLACE_ID"=TO_NUMBER(:B1))If i use literals than CBO uses cardinality =1 (I believe this is due it fix control :5483301 which i set to off In my environment)
select * from GC_FULFILLMENT_ITEMS where MARKETPLACE_ID=5 and GC_FULFILLMENT_STATUS_ID=2;
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 1 | 220 | 3 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| GC_FULFILLMENT_ITEMS | 1 | 220 | 3 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | I_GCFI_GCFS_ID_SDOC_MKTPLID | 1 | | 2 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("GC_FULFILLMENT_STATUS_ID"=2 AND "MARKETPLACE_ID"=5)
filter("MARKETPLACE_ID"=5)Here is column distribution and histogram information
Enter value for column_name: MARKETPLACE_ID
COLUMN_NAME ENDPOINT_VALUE CUMMULATIVE_FREQUENCY FREQUENCY ENDPOINT_ACTUAL_VALU
MARKETPLACE_ID 1 1 1
MARKETPLACE_ID 3 8548 8547
MARKETPLACE_ID 4 15608 7060
MARKETPLACE_ID 5 16385 777 --->
MARKETPLACE_ID 35691 16398 13
MARKETPLACE_ID 44551 16407 9
6 rows selected.
Enter value for column_name: GC_FULFILLMENT_STATUS_ID
COLUMN_NAME ENDPOINT_VALUE CUMMULATIVE_FREQUENCY FREQUENCY ENDPOINT_ACTUAL_VALU
GC_FULFILLMENT_STATUS_ID 5 19602 19602
GC_FULFILLMENT_STATUS_ID 6 19612 10
GC_FULFILLMENT_STATUS_ID 8 19802 190
3 rows selected.
Actual distribution
select MARKETPLACE_ID,count(*) from GC_FULFILLMENT_ITEMS group by MARKETPLACE_ID order by 1;
MARKETPLACE_ID COUNT(*)
1 2099
3 16339936
4 13358682
5 1471839 --->
35691 33623
44551 19881
78931 40273
101611 1
6309408
9 rows selected.
BHAVIK_DBA: GC1EU> select GC_FULFILLMENT_STATUS_ID,count(*) from GC_FULFILLMENT_ITEMS group by GC_FULFILLMENT_STATUS_ID order by 1;
GC_FULFILLMENT_STATUS_ID COUNT(*)
1 880
2 63 --->
3 24
5 37226908
6 22099
7 18
8 325409
9 343
8 rows selected.10053 trace
SINGLE TABLE ACCESS PATH
Table: GC_FULFILLMENT_ITEMS Alias: GC_FULFILLMENT_ITEMS
Card: Original: 36703588.000000 Rounded: 474909 Computed: 474909.06 Non Adjusted: 474909.06
Best:: AccessPath: IndexRange
Index: I_GCFI_GCFS_ID_SDOC_MKTPLID
Cost: 102.05 Degree: 1 Resp: 102.05 Card: 474909.06 Bytes: 0
Outline Data:
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.2')
DB_VERSION('11.2.0.2')
OPT_PARAM('_b_tree_bitmap_plans' 'false')
OPT_PARAM('_optim_peek_user_binds' 'false')
OPT_PARAM('_fix_control' '5483301:0')
ALL_ROWS
OUTLINE_LEAF(@"SEL$F5BB74E1")
MERGE(@"SEL$2")
OUTLINE(@"SEL$1")
OUTLINE(@"SEL$2")
INDEX_RS_ASC(@"SEL$F5BB74E1" "GC_FULFILLMENT_ITEMS"@"SEL$2" ("GC_FULFILLMENT_ITEMS"."GC_FULFILLMENT_STATUS_ID" "GC_FULFILLMENT_ITEMS"."SHIP_DELIVERY_OPTION_CODE" "GC_FULFILLMENT_ITEMS"."MARKETPLACE_ID"))
END_OUTLINE_DATA
*/Is there any reason why CBO is using card=474909.06 ? Having fix control () in place, it should have set card=1 if it is considering GC_FULFILLMENT_STATUS_ID= 2 as "rare" value..isn't it ?OraDBA02 wrote:
You are right Charles.
I was reading one of your blog and saw that.
As you said, it is an issue with SQLPLUS.
However, plan for the sql which is comming from application still shows the same (wrong cardinality) plan. It does not have TO_NUMBER function because of the reason that it does not experience data-type conversion that SQLPLUS has.
But YES...Plan is exactly the same with/without NO_NUMBER.OraDBA02,
I believe that some of the other people responding to this thread might have already described why the execution plan in the library cache is the same plan that you are seeing. One of the goals of using bind variables in SQL statements is to reduce the number of time consuming (and resource intensive) hard parses. That also means that a second goal is to share the same execution plan for future executions of the same SQL statement, even through bind variable values have changed. The catch here is that bind variable peeking, introduced with Oracle Database 9.0.1 (may be disabled by modifying a hidden parameter), helps the optimizer select the "best" (lowest calculated cost) execution plan for those specific bind variable values - the same plan may not be the "best" execution plan for other sets of bind variable values on future executions.
Histograms on one or more of the columns in the WHERE clause could either help or hinder the situation further. It might further help the first execution, but might further hinder future executions with different bind variable values. Oracle Database 11.1 introduced something called adaptive cursor sharing (and 11.2 introduced cardinality feedback) that in theory addresses issues where the execution plan should change for later executions with different bind variable values (but the SQL statement must execute poorly at least once).
There might be multiple child cursors in the library cache for the same SQL statement, each potentially with a different execution plan. I suggest finding the SQL_ID of the SQL statement that the application is submitting (you can do this by checking V$SQL or V$SQLAREA). Once you have the SQL_ID, go back to the SQL statement that I suggested for displaying the execution plan:
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'TYPICAL'));The first NULL in the above SQL statement is where you would specify the SQL_ID. If you leave the second NULL in place, the above SQL statement will retrieve the execution plan for all child cursors with that SQL_ID.
For instance, if the SQL_ID was 75chksrfa5fbt, you would execute the following:
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR('75chksrfa5fbt',NULL,'TYPICAL'));Usually, you can take it a step further to see the bind variables that were used during the optimization phase. To do that, you would add the +PEEKED_BINDS format parameter:
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR('75chksrfa5fbt',NULL,'TYPICAL +PEEKED_BINDS'));Note that there are various optimizer parameters that affect the optimizer's decisions, for instance, maybe the optimizer mode is set to FIRST_ROWS. Also possibly helpful is the +OUTLINE format parameter that might provide a clue regarding the value of some of the parameters affecting the optimizer. The SQL statement that you would then enter is similar to the following:
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY_CURSOR('75chksrfa5fbt',NULL,'TYPICAL +PEEKED_BINDS +OUTLINE'));Additional information might be helpful. Please see the following two forum threads to see what kind of information you should gather:
When your query takes too long… : When your query takes too long ...
How to post a SQL statement tuning request: HOW TO: Post a SQL statement tuning request - template posting
Charles Hooper
http://hoopercharles.wordpress.com/
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. -
What is p1 for direct path read temp wait event in 11gr1
hi friends,
When i run this query in my database(11gr1) i get this
SELECT P1,P1TEXT FROM V$ACTIVE_SESSION_HISTORY WHERE event='direct path write temp' and sql_id='2sd3hryy2baav';
P1 P1TEXT
1260 file number
As per the documentation given on the link
http://docs.oracle.com/cd/B28359_01/server.111/b28320/waitevents002.htm#
when i run the query for file#
select *
from v$datafile
where file# = file#;
i get no rows returned.
Can someone please tell me what is this value 1266??Hemant K Chitale wrote:
P1 as FILE_ID is actually the value of DB_FILES (an instance parameter) + the temp file id. Check if DB_FILES is set to 1250. In that case P1 of 1260 would mean the 10th TEMPFILE.
How did you came to know that P1.V$ACTIVE_SESSION_HISTORY = DB_FILES + the temp file id ?
Because when I checked in the docs it is saying :
P1 NUMBER First additional parameter
http://docs.oracle.com/cd/E11882_01/server.112/e25513/dynviews_1007.htm#REFRN30299
Kindly share with us the link, is possible please.
Regards
Girish Sharma -
Serial table scan with direct path read compared to db file scattered read
Hi,
The environment
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit
8K block size
db_file_multiblock_read_count is 128
show sga
Total System Global Area 1.6702E+10 bytes
Fixed Size 2219952 bytes
Variable Size 7918846032 bytes
Database Buffers 8724152320 bytes
Redo Buffers 57090048 bytes
16GB of SGA with 8GB of db buffer cache.
-- database is built on Solid State Disks
-- SQL trace and wait events
DBMS_MONITOR.SESSION_TRACE_ENABLE ( waits=>true )
-- The underlying table is called tdash. It has 1.7 Million rows based on data in all_objects. NO index
TABLE_NAME Rows Table Size/MB Used/MB Free/MB
TDASH 1,729,204 15,242 15,186 56
TABLE_NAME Allocated blocks Empty blocks Average space/KB Free list blocks
TDASH 1,943,823 7,153 805 0
Objectives
To show that when serial scans are performed on database built on Solid State Disks (SSD) compared to Magnetic disks (HDD), the performance gain is far less compared to random reads with index scans on SSD compared to HDD
Approach
We want to read the first 100 rows of tdash table randomly into buffer, taking account of wait events and wait times generated. The idea is that on SSD the wait times will be better compared to HDD but not that much given the serial nature of table scans.
The code used
ALTER SESSION SET TRACEFILE_IDENTIFIER = 'test_with_tdash_ssdtester_noindex';
DECLARE
type array is table of tdash%ROWTYPE index by binary_integer;
l_data array;
l_rec tdash%rowtype;
BEGIN
SELECT
a.*
,RPAD('*',4000,'*') AS PADDING1
,RPAD('*',4000,'*') AS PADDING2
BULK COLLECT INTO
l_data
FROM ALL_OBJECTS a;
DBMS_MONITOR.SESSION_TRACE_ENABLE ( waits=>true );
FOR rs IN 1 .. 100
LOOP
BEGIN
SELECT * INTO l_rec FROM tdash WHERE object_id = l_data(rs).object_id;
EXCEPTION
WHEN NO_DATA_FOUND THEN NULL;
END;
END LOOP;
END;
/Server is rebooted prior to any tests
Whern run as default, the optimizer (although some attribute this to the execution engine) chooses direct path read into PGA in preference to db file scattered read.
With this choice it takes 6,520 seconds to complete the query. The results are shown below
SQL ID: 78kxqdhk1ubvq
Plan Hash: 1148949653
SELECT *
FROM
TDASH WHERE OBJECT_ID = :B1
call count cpu elapsed disk query current rows
Parse 1 0.01 0.00 2 47 0 0
Execute 100 0.00 0.00 1 51 0 0
Fetch 100 10.88 6519.89 194142802 194831012 0 100
total 201 10.90 6519.90 194142805 194831110 0 100
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER) (recursive depth: 1)
Rows Row Source Operation
1 TABLE ACCESS FULL TDASH (cr=1948310 pr=1941430 pw=0 time=0 us cost=526908 size=8091 card=1)
Rows Execution Plan
0 SELECT STATEMENT MODE: ALL_ROWS
1 TABLE ACCESS MODE: ANALYZED (FULL) OF 'TDASH' (TABLE)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
Disk file operations I/O 3 0.00 0.00
db file sequential read 2 0.00 0.00
direct path read 1517504 0.05 6199.93
asynch descriptor resize 196 0.00 0.00
DECLARE
type array is table of tdash%ROWTYPE index by binary_integer;
l_data array;
l_rec tdash%rowtype;
BEGIN
SELECT
a.*
,RPAD('*',4000,'*') AS PADDING1
,RPAD('*',4000,'*') AS PADDING2
BULK COLLECT INTO
l_data
FROM ALL_OBJECTS a;
DBMS_MONITOR.SESSION_TRACE_ENABLE ( waits=>true );
FOR rs IN 1 .. 100
LOOP
BEGIN
SELECT * INTO l_rec FROM tdash WHERE object_id = l_data(rs).object_id;
EXCEPTION
WHEN NO_DATA_FOUND THEN NULL;
END;
END LOOP;
END;
call count cpu elapsed disk query current rows
Parse 0 0.00 0.00 0 0 0 0
Execute 1 3.84 4.03 320 48666 0 1
Fetch 0 0.00 0.00 0 0 0 0
total 1 3.84 4.03 320 48666 0 1
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.00 0.00
SQL ID: 9babjv8yq8ru3
Plan Hash: 0
BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END;
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 1
Fetch 0 0.00 0.00 0 0 0 0
total 2 0.00 0.00 0 0 0 1
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.00 0.00
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 2 3.84 4.03 320 48666 0 2
Fetch 0 0.00 0.00 0 0 0 0
total 3 3.84 4.03 320 48666 0 2
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 2 0.00 0.00
SQL*Net message from client 2 0.00 0.00
log file sync 1 0.00 0.00
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 9 0.01 0.00 2 47 0 0
Execute 129 0.01 0.00 1 52 2 1
Fetch 140 10.88 6519.89 194142805 194831110 0 130
total 278 10.91 6519.91 194142808 194831209 2 131
Misses in library cache during parse: 9
Misses in library cache during execute: 8
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
db file sequential read 5 0.00 0.00
Disk file operations I/O 3 0.00 0.00
direct path read 1517504 0.05 6199.93
asynch descriptor resize 196 0.00 0.00
102 user SQL statements in session.
29 internal SQL statements in session.
131 SQL statements in session.
1 statement EXPLAINed in this session.
Trace file: mydb_ora_16394_test_with_tdash_ssdtester_noindex.trc
Trace file compatibility: 11.1.0.7
Sort options: default
1 session in tracefile.
102 user SQL statements in trace file.
29 internal SQL statements in trace file.
131 SQL statements in trace file.
11 unique SQL statements in trace file.
1 SQL statements EXPLAINed using schema:
ssdtester.plan_table
Schema was specified.
Table was created.
Table was dropped.
1531657 lines in trace file.
6520 elapsed seconds in trace file.I then force the query not to use direct path read by invoking
ALTER SESSION SET EVENTS '10949 trace name context forever, level 1' -- No Direct path read ;In this case the optimizer uses db file scattered read predominantly and the query takes 4,299 seconds to finish which is around 34% faster than using direct path read (default).
The report is shown below
SQL ID: 78kxqdhk1ubvq
Plan Hash: 1148949653
SELECT *
FROM
TDASH WHERE OBJECT_ID = :B1
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 2 47 0 0
Execute 100 0.00 0.00 2 51 0 0
Fetch 100 143.44 4298.87 110348670 194490912 0 100
total 201 143.45 4298.88 110348674 194491010 0 100
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER) (recursive depth: 1)
Rows Row Source Operation
1 TABLE ACCESS FULL TDASH (cr=1944909 pr=1941430 pw=0 time=0 us cost=526908 size=8091 card=1)
Rows Execution Plan
0 SELECT STATEMENT MODE: ALL_ROWS
1 TABLE ACCESS MODE: ANALYZED (FULL) OF 'TDASH' (TABLE)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
Disk file operations I/O 3 0.00 0.00
db file sequential read 129759 0.01 17.50
db file scattered read 1218651 0.05 3770.02
latch: object queue header operation 2 0.00 0.00
DECLARE
type array is table of tdash%ROWTYPE index by binary_integer;
l_data array;
l_rec tdash%rowtype;
BEGIN
SELECT
a.*
,RPAD('*',4000,'*') AS PADDING1
,RPAD('*',4000,'*') AS PADDING2
BULK COLLECT INTO
l_data
FROM ALL_OBJECTS a;
DBMS_MONITOR.SESSION_TRACE_ENABLE ( waits=>true );
FOR rs IN 1 .. 100
LOOP
BEGIN
SELECT * INTO l_rec FROM tdash WHERE object_id = l_data(rs).object_id;
EXCEPTION
WHEN NO_DATA_FOUND THEN NULL;
END;
END LOOP;
END;
call count cpu elapsed disk query current rows
Parse 0 0.00 0.00 0 0 0 0
Execute 1 3.92 4.07 319 48625 0 1
Fetch 0 0.00 0.00 0 0 0 0
total 1 3.92 4.07 319 48625 0 1
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.00 0.00
SQL ID: 9babjv8yq8ru3
Plan Hash: 0
BEGIN DBMS_OUTPUT.GET_LINES(:LINES, :NUMLINES); END;
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 1
Fetch 0 0.00 0.00 0 0 0 0
total 2 0.00 0.00 0 0 0 1
Misses in library cache during parse: 0
Optimizer mode: ALL_ROWS
Parsing user id: 96 (SSDTESTER)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.00 0.00
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 2 3.92 4.07 319 48625 0 2
Fetch 0 0.00 0.00 0 0 0 0
total 3 3.92 4.07 319 48625 0 2
Misses in library cache during parse: 0
Misses in library cache during execute: 1
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 2 0.00 0.00
SQL*Net message from client 2 0.00 0.00
log file sync 1 0.00 0.00
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 9 0.01 0.00 2 47 0 0
Execute 129 0.00 0.00 2 52 2 1
Fetch 140 143.44 4298.87 110348674 194491010 0 130
total 278 143.46 4298.88 110348678 194491109 2 131
Misses in library cache during parse: 9
Misses in library cache during execute: 8
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
db file sequential read 129763 0.01 17.50
Disk file operations I/O 3 0.00 0.00
db file scattered read 1218651 0.05 3770.02
latch: object queue header operation 2 0.00 0.00
102 user SQL statements in session.
29 internal SQL statements in session.
131 SQL statements in session.
1 statement EXPLAINed in this session.
Trace file: mydb_ora_26796_test_with_tdash_ssdtester_noindex_NDPR.trc
Trace file compatibility: 11.1.0.7
Sort options: default
1 session in tracefile.
102 user SQL statements in trace file.
29 internal SQL statements in trace file.
131 SQL statements in trace file.
11 unique SQL statements in trace file.
1 SQL statements EXPLAINed using schema:
ssdtester.plan_table
Schema was specified.
Table was created.
Table was dropped.
1357958 lines in trace file.
4299 elapsed seconds in trace file.I note that there are 1,517,504 waits with direct path read with total time of nearly 6,200 seconds. In comparison with no direct path read, there are 1,218,651 db file scattered read waits with total wait time of 3,770 seconds. My understanding is that direct path read can use single or multi-block read into the PGA. However db file scattered reads do multi-block read into multiple discontinuous SGA buffers. So it is possible given the higher number of direct path waits that the optimizer cannot do multi-block reads (contigious buffers within PGA) and hence has to revert to single blocks reads which results in more calls and more waits?.
Appreciate any advise and apologies for being long winded.
Thanks,
MichHi Charles,
I am doing your tests for t1 table using my server.
Just to clarify my environment is:
I did the whole of this test on my server. My server has I7-980 HEX core processor with 24GB of RAM and 1 TB of HDD SATA II for test/scratch backup and archive. The operating system is RHES 5.2 64-bit installed on a 120GB OCZ Vertex 3 Series SATA III 2.5-inch Solid State Drive.
Oracle version installed was 11g Enterprise Edition Release 11.2.0.1.0 -64bit. The binaries were created on HDD. Oracle itself was configured with 16GB of SGA, of which 7.5GB was allocated to Variable Size and 8GB to Database Buffers.
For Oracle tablespaces including SYS, SYSTEM, SYSAUX, TEMPORARY, UNDO and redo logs, I used file systems on 240GB OCZ Vertex 3 Series SATA III 2.5-inch Solid State Drive. With 4K Random Read at 53,500 IOPS and 4K Random Write at 56,000 IOPS (manufacturer’s figures), this drive is probably one of the fastest commodity SSDs using NAND flash memory with Multi-Level Cell (MLC). Now my T1 table created as per your script and has the following rows and blocks (8k block size)
SELECT
NUM_ROWS,
BLOCKS
FROM
USER_TABLES
WHERE
TABLE_NAME='T1';
NUM_ROWS BLOCKS
12000000 178952which is pretty identical to yours.
Then I run the query as brelow
set timing on
ALTER SESSION SET TRACEFILE_IDENTIFIER = 'test_bed_T1';
ALTER SESSION SET EVENTS '10046 TRACE NAME CONTEXT FOREVER, LEVEL 8';
SELECT
COUNT(*)
FROM
T1
WHERE
RN=1;
which gives
COUNT(*)
60000
Elapsed: 00:00:05.29
tkprof output shows
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.02 5.28 178292 178299 0 1
total 4 0.02 5.28 178292 178299 0 1
Compared to yours:
Fetch 2 0.60 4.10 178493 178498 0 1
It appears to me that my CPU utilisation is by order of magnitude better but my elapsed time is worse!
Now the way I see it elapsed time = CPU time + wait time. Further down I have
Rows Row Source Operation
1 SORT AGGREGATE (cr=178299 pr=178292 pw=0 time=0 us)
60000 TABLE ACCESS FULL T1 (cr=178299 pr=178292 pw=0 time=42216 us cost=48697 size=240000 card=60000)
Rows Execution Plan
0 SELECT STATEMENT MODE: ALL_ROWS
1 SORT (AGGREGATE)
60000 TABLE ACCESS MODE: ANALYZED (FULL) OF 'T1' (TABLE)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 3 0.00 0.00
SQL*Net message from client 3 0.00 0.00
Disk file operations I/O 3 0.00 0.00
direct path read 1405 0.00 4.68
Your direct path reads are
direct path read 1404 0.01 3.40Which indicates to me you have faster disks compared to mine, whereas it sounds like my CPU is faster than yours.
With db file scattered read I get
Elapsed: 00:00:06.95
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 1.22 6.93 178293 178315 0 1
total 4 1.22 6.94 178293 178315 0 1
Rows Row Source Operation
1 SORT AGGREGATE (cr=178315 pr=178293 pw=0 time=0 us)
60000 TABLE ACCESS FULL T1 (cr=178315 pr=178293 pw=0 time=41832 us cost=48697 size=240000 card=60000)
Rows Execution Plan
0 SELECT STATEMENT MODE: ALL_ROWS
1 SORT (AGGREGATE)
60000 TABLE ACCESS MODE: ANALYZED (FULL) OF 'T1' (TABLE)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 2 0.00 0.00
Disk file operations I/O 3 0.00 0.00
db file sequential read 1 0.00 0.00
db file scattered read 1414 0.00 5.36
SQL*Net message from client 2 0.00 0.00
compared to your
db file scattered read 1415 0.00 4.16On the face of it with this test mine shows 21% improvement with direct path read compared to db scattered file read. So now I can go back to re-visit my original test results:
First default with direct path read
call count cpu elapsed disk query current rows
Parse 1 0.01 0.00 2 47 0 0
Execute 100 0.00 0.00 1 51 0 0
Fetch 100 10.88 6519.89 194142802 194831012 0 100
total 201 10.90 6519.90 194142805 194831110 0 100
CPU ~ 11 sec, elapsed ~ 6520 sec
wait stats
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
direct path read 1517504 0.05 6199.93
roughly 0.004 sec for each I/ONow with db scattered file read I get
call count cpu elapsed disk query current rows
Parse 1 0.00 0.00 2 47 0 0
Execute 100 0.00 0.00 2 51 0 0
Fetch 100 143.44 4298.87 110348670 194490912 0 100
total 201 143.45 4298.88 110348674 194491010 0 100
CPU ~ 143 sec, elapsed ~ 4299 sec
and waits:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
db file sequential read 129759 0.01 17.50
db file scattered read 1218651 0.05 3770.02
roughly 17.5/129759 = .00013 sec for single block I/O and 3770.02/1218651 = .0030 for multi-block I/ONow my theory is that the improvements comes from the large buffer cache (8320MB) inducing it to do some read aheads (async pre-fetch). Read aheads are like quasi logical I/Os and they will be cheaper compared to physical I/O. When there is large buffer cache and read aheads can be done then using buffer cache is a better choice than PGA?
Regards,
Mich -
Direct Path Read waits are not showing in Elapsed time
Hi,
I'm having a question regarding interpretation of a SQL trace file. I'm on Oracle 11.2.0.1 HP/UX 64 bit.
Following is only the overall result of the trace (it is quite big).
My question is about the Direct Path Read waits which are totallizing 268s of wait but are not showing in the fetch elapsed time (49.58s) and are not showing anywhere in the trace except in the overall result.
I do not understand why it is not part of the Elapsed time...
For info, the trace is for the specific session that was performing all the required queries to display an online report. The database is accessed by the Java application using Hybernate.
The trace was obtained by the following SQL:
exec sys.dbms_monitor.serv_mod_act_trace_enable(service_name=>'SYS$USERS',waits=>true,binds=>true);Then I query the sessions to find the one created by the application.
OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 36 0.43 0.51 0 5 0 0
Execute 62 0.01 0.01 0 0 0 0
Fetch 579 4.01 49.06 3027 153553 0 5516
total 677 4.45 49.58 3027 153558 0 5516
Misses in library cache during parse: 29
Misses in library cache during execute: 2
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 32754 0.00 0.03
SQL*Net message from client 32753 2.33 232.01
Disk file operations I/O 179 0.00 0.02
db file sequential read 2979 0.54 45.72
SQL*Net more data to client 133563 0.04 5.30
direct path read 34840 0.94 268.21
SQL*Net more data from client 1075 0.00 0.02
db file scattered read 6 0.03 0.11
asynch descriptor resize 52 0.00 0.00
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
call count cpu elapsed disk query current rows
Parse 25 0.00 0.02 0 0 0 0
Execute 58 0.05 0.04 0 0 0 0
Fetch 126 0.00 0.04 4 161 0 123
total 209 0.05 0.11 4 161 0 123
Misses in library cache during parse: 3
Misses in library cache during execute: 3
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
Disk file operations I/O 1 0.00 0.00
db file sequential read 4 0.01 0.03
asynch descriptor resize 1 0.00 0.00
37 user SQL statements in session.
57 internal SQL statements in session.
94 SQL statements in session.
Trace file: oxd1ta00_ora_16542.trc
Trace file compatibility: 11.1.0.7
Sort options: default
1 session in tracefile.
37 user SQL statements in trace file.
57 internal SQL statements in trace file.
94 SQL statements in trace file.
57 unique SQL statements in trace file.
241517 lines in trace file.
568 elapsed seconds in trace file.Thanks
ChristopheChristophe Lize wrote:
Closing this thread even if it's not answered...Sorry, I don't have time to test this myself now, but you shouldn't mark this thread as answered if it is not, because other people might find it and think they find an answer if they have a similar question.
I suggest you try the following to narrow down things:
1. Open the RAW trace file and check the cursor numbers of the "direct path reads" - check if you can find any references for those cursor numbers manually. The cursor numbers are those numbers behind the WAIT #<xx>, and you can check if you find any other entry unequal to WAIT #<xx> with the same #<xx>, for example EXEC #<xx> or FETCH #<xx>
A short primer on how to interpret the raw trace file can also be found in MOS document 39817.1
2. Run the RAW trace file through alternative free trace file analyzers like SQLDeveloper (yes it can process raw trace files), OraSRP or Christian Antognini's TVD$XTAT. If you have My Oracle Support access you can also try Oracle's own extended Trace Analyzer (TRCA / TRCANLZR). See MOS Note 224270.1
Check if these tools tell you more about your specific wait event and oddities with the trace file in general.
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
Co-author of the "OakTable Expert Oracle Practices" book:
http://www.apress.com/book/view/1430226684
http://www.amazon.com/Expert-Oracle-Practices-Database-Administration/dp/1430226684 -
A lot of messages "direct path write temp" and "direct path read temp"
Hello, all
Please, understand me, what is going on in my system (DB: Oracle database 11.2.0.3, OS: Windows 2008 R2).
In AWR report (1 hour) I see next:
Foreground Wait Events
Avg
%Time Total Wait wait Waits % DB
Event Waits -outs Time (s) (ms) /txn time
direct path write temp 132,627 0 1,056 8 0.8 21.7
direct path read temp 308,969 0 565 2 2.0 11.6
log file sync 19,228 0 241 13 0.1 5.0
direct path write 17,698 0 135 8 0.1 2.8
db file sequential read 21,149 0 94 4 0.1 1.9
SQL*Net message from dblin 59 0 5 86 0.0 .1
Segments by Direct Physical Reads DB/Inst: SGRE/sgre Snaps: 1039-1040
-> Total Direct Physical Reads: 392,273
-> Captured Segments account for 94.7% of Total
Tablespace Subobject Obj. Direct
Owner Name Object Name Name Type Reads %Total
** MISSING TEMP ** TRANSIENT: 437734 MISSING ** UNDEF 38,290 9.76
DBSNMP TEMP MGMT_TEMPT_SQL TABLE 38,242 9.75
** MISSING TEMP ** TRANSIENT: 438784 MISSING ** UNDEF 37,790 9.63
** MISSING TEMP ** TRANSIENT: 437312 MISSING ** UNDEF 37,661 9.60
** MISSING TEMP ** TRANSIENT: 439257 MISSING ** UNDEF 37,477 9.55Some selects:
SELECT S.sid,
T.blocks * TBS.block_size / 1024 / 1024 mb_used, T.tablespace, T.SEGTYPE
FROM v$sort_usage T, v$session S, v$sqlarea Q, dba_tablespaces TBS
WHERE T.session_addr = S.saddr
AND T.sqladdr = Q.address (+)
AND T.tablespace = TBS.tablespace_name
AND S.sid = 732
ORDER BY S.username, S.sid;
SID MB_USED TABLESPACE SEGTYPE
732 2 TEMP LOB_DATA
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP INDEX
732 1 TEMP DATA
732 1 TEMP INDEX
732 1 TEMP LOB_INDEX
select st.sid, sn.name, st.VALUE
from V$statname sn, v$sesstat st
where st.STATISTIC# = sn.STATISTIC#
and (sn.name like 'sorts%')
and st.sid in (select sid from v$session_wait where event like '%direct path write temp%')
order by st.sid
SID NAME VALUE
732 sorts (memory) 591408
732 sorts (rows) 102126
732 sorts (disk) 0Why I do not see any disk sorts? If TEMP is used for no sort operations, then for which operations?
How I can see that? How can I decrease direct path write temp without tuning SQL?
Additional information:
PGA_AGGREGATE_TARGET is set to big value - 6GB (3GB enough due to advisory recommendation)
Please, help.
Regards, user12103911.user12103911 wrote:
SELECT optimal_count, round(optimal_count*100/total, 2) optimal_perc,
onepass_count, round(onepass_count*100/total, 2) onepass_perc,
multipass_count, round(multipass_count*100/total, 2) multipass_perc
FROM
(SELECT decode(sum(total_executions), 0, 1, sum(total_executions)) total,
sum(OPTIMAL_EXECUTIONS) optimal_count,
sum(ONEPASS_EXECUTIONS) onepass_count,
sum(MULTIPASSES_EXECUTIONS) multipass_count
FROM v$sql_workarea_histogram);
OPTIMAL_COUNT OPTIMAL_PERC ONEPASS_COUNT ONEPASS_PERC MULTIPASS_COUNT MULTIPASS_PERC
13150685 100 0 0 0 0No n-pass executions.That's a pretty convincing display - given that your AWR manages to NAME an object that is in the TEMP tablespace, an obvious point to follow up is global temporary tables. If you have any declared as "on commit preserve" (duration = 'SYS$SESSION') then you could have code which does "insert /*+ append */ into gtt", and if you then query this in parallel (or - since you're on 11.2.0.3 - the data volume is large enough) Oracle could choose to do direct path writes to load the GTT and direct path reads to read it back.
Regards
Jonathan Lewis
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