Read by other session wait event
I have some reports in my database that whenever executed by two or more session these reports suffers with read by other session wait event. Tables which are involving in that's query i moves them to other tablespace and then move back to original tablespace. Some how this could solves read by other session wait event. But after some days these problem occur again.
How can i permanently solve this problem??
My db is Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod
Oracle Block size 4096
Thanks
Hi there,
Searching for this wait eventin the docs gave this,
http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/waitevents003.htm#sthref3159
read by other session
This event occurs when a session requests a buffer that is currently being read into the buffer cache by another session. Prior to release 10.1, waits for this event were grouped with the other reasons for waiting for buffers under the 'buffer busy wait' event
Wait Time: Time waited for the buffer to be read by the other session (in microseconds)And a quick google search for the same gave these results in the top.
http://www.confio.com/English/Tips/Read_By_Other_Session.php
http://www.dbafan.com/blog/?p=132
HTH
Aman....
Similar Messages
-
Hi all,
I have a query with very little cost, it only access one row of the table from a primary key and joins it another table again on primary key column. It doesn't even take a second to complete.
But the problem is when there is another session that accesses data from one of the tables, I encounter "read by other session" wait event, so I wonder if there is a hint to overcome this wait, that will force query to make a disk read without waiting any other working session to put it into buffer cache. Or any other suggestions?
Thanksseth2 wrote:
Hi all,
I have a query with very little cost, it only access one row of the table from a primary key and joins it another table again on primary key column. It doesn't even take a second to complete.
You also say in a later post that the cost of the plan is 11 - if this is correct then your two indexes must have a blevel of about 5 to get that cost from that plan. It seems highly likely that your query doesn't always take the plan you expect and that the "10 minute" versions of this query (which should take less than 0.1 seconds on any reasonable system) is doing a large tablescan to spend so much extra time and report "read by other session". I would check v$sql for multiple child cursors and v$sql_plan (using dbms_xplan.display_cursor if you're on 10g) to check executions plans.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.
"Science is more than a body of knowledge; it is a way of thinking"
Carl Sagan -
Issue with "read by other session" and a parallel MERGE query
Hi everyone,
we have run into an issue with a batch process updating a large table (12 million rows / a few GB, so it's not that large). The process is quite simple - load the 'increment' from a file into a working table (INCREMENT_TABLE) and apply it to the main table using a MERGE. The increment is rather small (usually less than 10k rows), but the MERGE runs for hours (literally) although the execution plan seems quite reasonable (can post it tomorrow, if needed).
The first thing we've checked is AWR report, and we've noticed this:
Top 5 Timed Foreground Events
Event Waits Time(s) Avg wait (ms) % DB time Wait Class
DB CPU 10,086 43.82
read by other session 3,968,673 9,179 2 39.88 User I/O
db file scattered read 1,058,889 2,307 2 10.02 User I/O
db file sequential read 408,499 600 1 2.61 User I/O
direct path read 132,430 459 3 1.99 User I/OSo obviously most of the time was consumed by "read by other session" wait event. There were no other queries running at the server, so in this case "other session" actually means "parallel processes" used to execute the same query. The main table (the one that's updated by the batch process) has "PARALLEL DEGREE 4" so Oracle spawns 4 processes.
I'm not sure how to fix this. I've read a lot of details about "read by other session" but I'm not sure it's the root cause - in the end, when two processes read the same block, it's quite natural that only one does the physical I/O while the other waits. What really seems suspicious is the number of waits - 4 million waits means 4 million blocks, 8kB each. That's about 32GB - the table has about 4GB, and there are less than 10k rows updated. So 32 GB is a bit overkill (OK, there are indexes etc. but still, that's 8x the size of the table).
So I'm thinking that the buffer cache is too small - one process reads the data into cache, then it's removed and read again. And again ...
One of the recommendations I've read was to increase the PCTFREE, to eliminate 'hot blocks' - but wouldn't that make the problem even worse (more blocks to read and keep in the cache)? Or am I completely wrong?
The database is 11gR2, the buffer cache is about 4GB. The storage is a SAN (but I don't think this is the bottleneck - according to the iostat results it performs much better in case of other batch jobs).OK, so a bit more details - we've managed to significantly decrease the estimated cost and runtime. All we had to do was a small change in the SQL - instead of
MERGE /*+ parallel(D DEFAULT)*/ INTO T_NOTUNIFIED_CLIENT D /*+ append */
USING (SELECT
FROM TMP_SODW_BB) S
ON (D.NCLIENT_KEY = S.NCLIENT_KEY AND D.CURRENT_RECORD = 'Y' AND S.DIFF_FLAG IN ('U', 'D'))
...(which is the query listed above) we have done this
MERGE /*+ parallel(D DEFAULT)*/ INTO T_NOTUNIFIED_CLIENT D /*+ append */
USING (SELECT
FROM TMP_SODW_BB AND DIFF_FLAG IN ('U', 'D')) S
ON (D.NCLIENT_KEY = S.NCLIENT_KEY AND D.CURRENT_RECORD = 'Y')
...i.e. we have moved the condition from the MERGE ON clause to the SELECT. And suddenly, the execution plan is this
OPERATION OBJECT_NAME OPTIONS COST
MERGE STATEMENT 239
MERGE T_NOTUNIFIED_CLIENT
PX COORDINATOR
PX SEND :TQ10000 QC (RANDOM) 239
VIEW
NESTED LOOPS OUTER 239
PX BLOCK ITERATOR
TABLE ACCESS TMP_SODW_BB FULL 2
Filter Predicates
OR
DIFF_FLAG='D'
DIFF_FLAG='U'
TABLE ACCESS T_NOTUNIFIED_CLIENT BY INDEX ROWID 3
INDEX AK_UQ_NOTUNIF_T_NOTUNI RANGE SCAN 2
Access Predicates
AND
D.NCLIENT_KEY(+)=NCLIENT_KEY
D.CURRENT_RECORD(+)='Y'
Filter Predicates
D.CURRENT_RECORD(+)='Y' Yes, I know the queries are not exactly the same - but we can fix that. The point is that the TMP_SODW_BB table contains 1639 rows in total, and 284 of them match the moved 'IN' condition. Even if we remove the condition altogether (i.e. 1639 rows have to be merged), the execution plan does not change (the cost increases to about 1300, which is proportional to the number of rows).
But with the original IN condition (that turns into an OR combination of predicates) in the MERGE ON clausule, the cost suddenly skyrockets to 990.000 and it's damn slow. It seems like a problem with cost estimation, because once we remove one of the values (so there's only one value in the IN clausule), it works fine again. So I guess it's a planner/estimator issue ... -
Performance issue showing read by other session Event
Hi All,
we are having a severe performance issue in my database when we are running batch jobs.
This was a new database(11.2.0.2) and we are testing the performance by running some batch jobs. These batch jobs included some inserts and updates.
I am seeing read by other session in top 5 timed events and cache buffers chains in Latch Miss Sources section.
Please help me to solve this out.
Inst Num Startup Time Release RAC
1 27-Feb-12 09:03 11.2.0.2.0 NO
Platform CPUs Cores Sockets Memory(GB)
Linux x86 64-bit 8 8 8 48.00
Snap Id Snap Time Sessions Curs/Sess
Begin Snap: 5605 29-Feb-12 03:00:27 63 4.5
End Snap: 5614 29-Feb-12 12:00:47 63 4.3
Elapsed: 540.32 (mins)
DB Time: 1,774.23 (mins)
Cache Sizes Begin End
~~~~~~~~~~~ ---------- ----------
Buffer Cache: 1,952M 1,952M Std Block Size: 16K
Shared Pool Size: 1,024M 1,024M Log Buffer: 18,868K
Load Profile Per Second Per Transaction Per Exec Per Call
~~~~~~~~~~~~ --------------- --------------- ---------- ----------
DB Time(s): 3.3 0.8 0.02 0.05
DB CPU(s): 1.1 0.3 0.01 0.02
Redo size: 55,763.8 13,849.3
Logical reads: 23,906.6 5,937.4
Block changes: 325.7 80.9
Physical reads: 665.6 165.3
Physical writes: 40.4 10.0
User calls: 60.7 15.1
Parses: 10.6 2.6
Hard parses: 1.1 0.3
W/A MB processed: 0.6 0.2
Logons: 0.1 0.0
Executes: 151.2 37.6
Rollbacks: 0.0 0.0
Transactions: 4.0
Instance Efficiency Percentages (Target 100%)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Buffer Nowait %: 99.94 Redo NoWait %: 100.00
Buffer Hit %: 97.90 In-memory Sort %: 100.00
Library Hit %: 98.06 Soft Parse %: 90.16
Execute to Parse %: 92.96 Latch Hit %: 100.00
Parse CPU to Parse Elapsd %: 76.71 % Non-Parse CPU: 98.57
Shared Pool Statistics Begin End
Memory Usage %: 89.38 87.96
% SQL with executions>1: 97.14 95.15
% Memory for SQL w/exec>1: 96.05 92.46
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Avg
wait % DB
Event Waits Time(s) (ms) time Wait Class
db file sequential read 14,092,706 65,613 5 61.6 User I/O
DB CPU 34,819 32.7
read by other session 308,534 1,260 4 1.2 User I/O
direct path read 97,454 987 10 .9 User I/O
db file scattered read 71,870 910 13 .9 User I/O
Host CPU (CPUs: 8 Cores: 8 Sockets: 8)
~~~~~~~~ Load Average
Begin End %User %System %WIO %Idle
0.43 0.36 13.7 0.6 9.7 85.7
Instance CPU
~~~~~~~~~~~~
% of total CPU for Instance: 13.5
% of busy CPU for Instance: 94.2
%DB time waiting for CPU - Resource Mgr: 0.0
Memory Statistics
~~~~~~~~~~~~~~~~~ Begin End
Host Mem (MB): 49,152.0 49,152.0
SGA use (MB): 3,072.0 3,072.0
PGA use (MB): 506.5 629.1
% Host Mem used for SGA+PGA: 7.28 7.53
Time Model Statistics
-> Total time in database user-calls (DB Time): 106453.8s
-> Statistics including the word "background" measure background process
time, and so do not contribute to the DB time statistic
-> Ordered by % or DB time desc, Statistic name
Statistic Name Time (s) % of DB Time
sql execute elapsed time 105,531.1 99.1
DB CPU 34,818.8 32.7
parse time elapsed 714.7 .7
hard parse elapsed time 684.8 .6
PL/SQL execution elapsed time 161.9 .2
PL/SQL compilation elapsed time 44.2 .0
connection management call elapsed time 16.9 .0
hard parse (sharing criteria) elapsed time 10.2 .0
hard parse (bind mismatch) elapsed time 9.4 .0
sequence load elapsed time 2.9 .0
repeated bind elapsed time 0.5 .0
failed parse elapsed time 0.0 .0
DB time 106,453.8
background elapsed time 1,753.9
background cpu time 61.7
Operating System Statistics
-> *TIME statistic values are diffed.
All others display actual values. End Value is displayed if different
-> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name
Statistic Value End Value
BUSY_TIME 3,704,415
IDLE_TIME 22,203,740
IOWAIT_TIME 2,517,864
NICE_TIME 3
SYS_TIME 145,696
USER_TIME 3,557,758
LOAD 0 0
RSRC_MGR_CPU_WAIT_TIME 0
VM_IN_BYTES 358,813,045,760
VM_OUT_BYTES 29,514,830,848
PHYSICAL_MEMORY_BYTES 51,539,607,552
NUM_CPUS 8
NUM_CPU_CORES 8
NUM_CPU_SOCKETS 8
GLOBAL_RECEIVE_SIZE_MAX 4,194,304
GLOBAL_SEND_SIZE_MAX 1,048,586
TCP_RECEIVE_SIZE_DEFAULT 87,380
TCP_RECEIVE_SIZE_MAX 4,194,304
TCP_RECEIVE_SIZE_MIN 4,096
TCP_SEND_SIZE_DEFAULT 16,384
TCP_SEND_SIZE_MAX 4,194,304
TCP_SEND_SIZE_MIN 4,096
Operating System Statistics -
Snap Time Load %busy %user %sys %idle %iowait
29-Feb 03:00:27 0.4 N/A N/A N/A N/A N/A
29-Feb 04:00:35 1.4 11.9 11.2 0.6 88.1 14.3
29-Feb 05:00:41 1.7 13.8 13.2 0.6 86.2 15.8
29-Feb 06:00:48 1.5 14.0 13.5 0.6 86.0 12.3
29-Feb 07:01:00 1.8 16.3 15.8 0.5 83.7 10.4
29-Feb 08:00:12 2.6 23.2 22.5 0.6 76.8 12.6
29-Feb 09:00:26 1.3 16.6 16.0 0.5 83.4 5.7
29-Feb 10:00:33 1.2 13.8 13.3 0.5 86.2 2.0
29-Feb 11:00:43 1.3 14.5 14.0 0.5 85.5 3.8
29-Feb 12:00:47 0.4 4.9 4.2 0.7 95.1 10.6
Foreground Wait Class
-> s - second, ms - millisecond - 1000th of a second
-> ordered by wait time desc, waits desc
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
-> Captured Time accounts for 97.9% of Total DB time 106,453.79 (s)
-> Total FG Wait Time: 69,415.64 (s) DB CPU time: 34,818.79 (s)
Avg
%Time Total Wait wait
Wait Class Waits -outs Time (s) (ms) %DB time
User I/O 14,693,843 0 69,222 5 65.0
DB CPU 34,819 32.7
Commit 40,629 0 119 3 0.1
System I/O 26,504 0 57 2 0.1
Network 1,945,010 0 11 0 0.0
Other 125,200 99 4 0 0.0
Application 2,673 0 2 1 0.0
Concurrency 3,059 0 1 0 0.0
Configuration 31 19 0 15 0.0
Foreground Wait Events
-> s - second, ms - millisecond - 1000th of a second
-> Only events with Total Wait Time (s) >= .001 are shown
-> ordered by wait time desc, waits desc (idle events last)
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
Avg
%Time Total Wait wait Waits % DB
Event Waits -outs Time (s) (ms) /txn time
db file sequential read 14,092,706 0 65,613 5 108.0 61.6
read by other session 308,534 0 1,260 4 2.4 1.2
direct path read 97,454 0 987 10 0.7 .9
db file scattered read 71,870 0 910 13 0.6 .9
db file parallel read 35,001 0 372 11 0.3 .3
log file sync 40,629 0 119 3 0.3 .1
control file sequential re 26,504 0 57 2 0.2 .1
direct path read temp 14,499 0 49 3 0.1 .0
direct path write temp 9,186 0 28 3 0.1 .0
SQL*Net message to client 1,923,973 0 5 0 14.7 .0
SQL*Net message from dblin 1,056 0 5 5 0.0 .0
Disk file operations I/O 8,848 0 2 0 0.1 .0
ASM file metadata operatio 36 0 2 54 0.0 .0
SQL*Net break/reset to cli 2,636 0 1 1 0.0 .0
ADR block file read 472 0 1 1 0.0 .0
os thread startup 8 0 1 74 0.0 .0
SQL*Net more data to clien 17,656 0 1 0 0.1 .0
asynch descriptor resize 123,852 100 0 0 0.9 .0
local write wait 110 0 0 4 0.0 .0
utl_file I/O 55,635 0 0 0 0.4 .0
log file switch (private s 8 0 0 52 0.0 .0
cursor: pin S wait on X 2 0 0 142 0.0 .0
enq: KO - fast object chec 13 0 0 20 0.0 .0
PX Deq: Slave Session Stat 248 0 0 1 0.0 .0
enq: RO - fast object reus 18 0 0 11 0.0 .0
latch: cache buffers chain 2,511 0 0 0 0.0 .0
latch: shared pool 195 0 0 1 0.0 .0
CSS initialization 12 0 0 8 0.0 .0
PX qref latch 54 100 0 2 0.0 .0
SQL*Net more data from cli 995 0 0 0 0.0 .0
SQL*Net more data from dbl 300 0 0 0 0.0 .0
kksfbc child completion 1 100 0 56 0.0 .0
library cache: mutex X 244 0 0 0 0.0 .0
PX Deq: Signal ACK RSG 124 0 0 0 0.0 .0
undo segment extension 6 100 0 7 0.0 .0
PX Deq: Signal ACK EXT 124 0 0 0 0.0 .0
library cache load lock 3 0 0 9 0.0 .0
ADR block file write 45 0 0 1 0.0 .0
CSS operation: action 12 0 0 2 0.0 .0
reliable message 28 0 0 1 0.0 .0
CSS operation: query 72 0 0 0 0.0 .0
latch: row cache objects 14 0 0 1 0.0 .0
enq: SQ - contention 17 0 0 0 0.0 .0
latch free 32 0 0 0 0.0 .0
buffer busy waits 52 0 0 0 0.0 .0
enq: PS - contention 16 0 0 0 0.0 .0
enq: TX - row lock content 6 0 0 1 0.0 .0
SQL*Net message to dblink 1,018 0 0 0 0.0 .0
cursor: pin S 23 0 0 0 0.0 .0
latch: cache buffers lru c 8 0 0 0 0.0 .0
SQL*Net message from clien 1,923,970 0 944,508 491 14.7
jobq slave wait 66,732 100 33,334 500 0.5
Streams AQ: waiting for me 6,481 100 32,412 5001 0.0
wait for unread message on 32,858 98 32,411 986 0.3
PX Deq: Execution Msg 1,448 0 190 131 0.0
PX Deq: Execute Reply 1,196 0 74 62 0.0
HS message to agent 228 0 4 19 0.0
single-task message 42 0 4 97 0.0
PX Deq Credit: send blkd 904 0 2 3 0.0
PX Deq Credit: need buffer 205 0 1 3 0.0
Foreground Wait Events
-> s - second, ms - millisecond - 1000th of a second
-> Only events with Total Wait Time (s) >= .001 are shown
-> ordered by wait time desc, waits desc (idle events last)
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
Avg
%Time Total Wait wait Waits % DB
Event Waits -outs Time (s) (ms) /txn time
PX Deq: Table Q Normal 4,291 0 1 0 0.0
PX Deq: Join ACK 124 0 0 1 0.0
PX Deq: Parse Reply 124 0 0 0 0.0
KSV master wait 256 0 0 0 0.0
Latch Miss Sources
-> only latches with sleeps are shown
-> ordered by name, sleeps desc
NoWait Waiter
Latch Name Where Misses Sleeps Sleeps
ASM map operation freeli kffmTranslate2 0 2 0
DML lock allocation ktadmc 0 2 0
FOB s.o list latch ksfd_allfob 0 2 2
In memory undo latch ktiFlushMe 0 5 0
In memory undo latch ktichg: child 0 3 0
PC and Classifier lists No latch 0 6 0
Real-time plan statistic keswxAddNewPlanEntry 0 20 20
SQL memory manager worka qesmmIRegisterWorkArea:1 0 1 1
active service list kswslogon: session logout 0 23 12
active service list kswssetsvc: PX session swi 0 6 1
active service list kswsite: service iterator 0 1 0
archive process latch kcrrgpll 0 3 3
cache buffers chains kcbgtcr_2 0 1,746 573
cache buffers chains kcbgtcr: fast path (cr pin 0 1,024 2,126
cache buffers chains kcbgcur_2 0 60 8
cache buffers chains kcbchg1: kslbegin: bufs no 0 16 3
cache buffers chains kcbgtcr: fast path 0 14 20
cache buffers chains kcbzibmlt: multi-block rea 0 10 0
cache buffers chains kcbrls_2 0 9 53
cache buffers chains kcbgtcr: kslbegin shared 0 8 1
cache buffers chains kcbrls_1 0 7 84
cache buffers chains kcbgtcr: kslbegin excl 0 6 14
cache buffers chains kcbnew: new latch again 0 6 0
cache buffers chains kcbzgb: scan from tail. no 0 6 0
cache buffers chains kcbzwb 0 5 8
cache buffers chains kcbgcur: fast path (shr) 0 3 0
cache buffers chains kcbget: pin buffer 0 3 0
cache buffers chains kcbzhngcbk2_1 0 1 0
cache buffers lru chain kcbzgws 0 19 0
cache buffers lru chain kcbo_link_q 0 3 0
call allocation ksuxds 0 14 10
call allocation ksudlp: top call 0 2 3
enqueue hash chains ksqgtl3 0 2 1
enqueue hash chains ksqrcl 0 1 2
enqueues ksqgel: create enqueue 0 1 0
object queue header oper kcbo_unlink_q 0 5 2
object queue header oper kcbo_sw_buf 0 2 0
object queue header oper kcbo_link_q 0 1 2
object queue header oper kcbo_switch_cq 0 1 2
object queue header oper kcbo_switch_mq_bg 0 1 4
parallel query alloc buf kxfpbalo 0 1 1
process allocation ksucrp:1 0 2 0
process queue reference kxfpqrsnd 0 1 0
qmn task queue latch kwqmnmvtsks: delay to read 0 1 0
redo allocation kcrfw_redo_gen: redo alloc 0 17 0
row cache objects kqreqd: reget 0 6 0
row cache objects kqrpre: find obj 0 6 13
row cache objects kqrso 0 2 0
row cache objects kqreqd 0 1 2
row cache objects kqrpre: init complete 0 1 1
shared pool kghalo 0 199 106
shared pool kghupr1 0 39 109
shared pool kghfre 0 18 19
shared pool kghalp 0 7 29
space background task la ktsj_grab_task 0 21 27
Mutex Sleep Summary
-> ordered by number of sleeps desc
Wait
Mutex Type Location Sleeps Time (ms)
Library Cache kglhdgn2 106 338 12
Library Cache kgllkc1 57 259 10
Library Cache kgllkdl1 85 123 21
Cursor Pin kkslce [KKSCHLPIN2] 70 286
Library Cache kglget2 2 31 1
Library Cache kglhdgn1 62 31 2
Library Cache kglpin1 4 26 1
Library Cache kglpnal1 90 18 0
Library Cache kglpndl1 95 15 2
Library Cache kgllldl2 112 6 0
Library Cache kglini1 32 1 0
-------------------------------------------------------------Thanks in advance.Hi,
Thanks for reply.
I provided one hour report.
Inst Num Startup Time Release RAC
1 27-Feb-12 09:03 11.2.0.2.0 NO
Platform CPUs Cores Sockets Memory(GB)
Linux x86 64-bit 8 8 8 48.00
Snap Id Snap Time Sessions Curs/Sess
Begin Snap: 5606 29-Feb-12 04:00:35 63 3.7
End Snap: 5607 29-Feb-12 05:00:41 63 3.6
Elapsed: 60.11 (mins)
DB Time: 382.67 (mins)
Cache Sizes Begin End
~~~~~~~~~~~ ---------- ----------
Buffer Cache: 1,952M 1,952M Std Block Size: 16K
Shared Pool Size: 1,024M 1,024M Log Buffer: 18,868K
Load Profile Per Second Per Transaction Per Exec Per Call
~~~~~~~~~~~~ --------------- --------------- ---------- ----------
DB Time(s): 6.4 0.8 0.03 0.03
DB CPU(s): 1.0 0.1 0.00 0.00
Redo size: 84,539.3 10,425.6
Logical reads: 23,345.6 2,879.1
Block changes: 386.5 47.7
Physical reads: 1,605.0 197.9
Physical writes: 7.1 0.9
User calls: 233.9 28.9
Parses: 4.0 0.5
Hard parses: 0.1 0.0
W/A MB processed: 0.1 0.0
Logons: 0.1 0.0
Executes: 210.9 26.0
Rollbacks: 0.0 0.0
Transactions: 8.1
Instance Efficiency Percentages (Target 100%)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Buffer Nowait %: 99.62 Redo NoWait %: 100.00
Buffer Hit %: 95.57 In-memory Sort %: 100.00
Library Hit %: 99.90 Soft Parse %: 98.68
Execute to Parse %: 98.10 Latch Hit %: 99.99
Parse CPU to Parse Elapsd %: 32.08 % Non-Parse CPU: 99.90
Shared Pool Statistics Begin End
Memory Usage %: 89.25 89.45
% SQL with executions>1: 96.79 97.52
% Memory for SQL w/exec>1: 95.67 96.56
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Avg
wait % DB
Event Waits Time(s) (ms) time Wait Class
db file sequential read 3,054,464 17,002 6 74.0 User I/O
DB CPU 3,748 16.3
read by other session 199,603 796 4 3.5 User I/O
direct path read 46,301 439 9 1.9 User I/O
db file scattered read 21,113 269 13 1.2 User I/O
Host CPU (CPUs: 8 Cores: 8 Sockets: 8)
~~~~~~~~ Load Average
Begin End %User %System %WIO %Idle
1.45 1.67 13.2 0.6 15.8 86.2
Instance CPU
~~~~~~~~~~~~
% of total CPU for Instance: 13.0
% of busy CPU for Instance: 94.7
%DB time waiting for CPU - Resource Mgr: 0.0
Memory Statistics
~~~~~~~~~~~~~~~~~ Begin End
Host Mem (MB): 49,152.0 49,152.0
SGA use (MB): 3,072.0 3,072.0
PGA use (MB): 513.5 467.7
% Host Mem used for SGA+PGA: 7.29 7.20
Time Model Statistics
-> Total time in database user-calls (DB Time): 22960.5s
-> Statistics including the word "background" measure background process
time, and so do not contribute to the DB time statistic
-> Ordered by % or DB time desc, Statistic name
Statistic Name Time (s) % of DB Time
sql execute elapsed time 22,835.9 99.5
DB CPU 3,748.4 16.3
parse time elapsed 15.4 .1
hard parse elapsed time 14.3 .1
PL/SQL execution elapsed time 7.5 .0
PL/SQL compilation elapsed time 6.0 .0
connection management call elapsed time 1.6 .0
sequence load elapsed time 0.4 .0
hard parse (sharing criteria) elapsed time 0.0 .0
repeated bind elapsed time 0.0 .0
failed parse elapsed time 0.0 .0
DB time 22,960.5
background elapsed time 238.1
background cpu time 4.9
Operating System Statistics
-> *TIME statistic values are diffed.
All others display actual values. End Value is displayed if different
-> ordered by statistic type (CPU Use, Virtual Memory, Hardware Config), Name
Statistic Value End Value
BUSY_TIME 396,506
IDLE_TIME 2,483,725
IOWAIT_TIME 455,495
NICE_TIME 0
SYS_TIME 16,163
USER_TIME 380,052
LOAD 1 2
RSRC_MGR_CPU_WAIT_TIME 0
VM_IN_BYTES 95,646,943,232
VM_OUT_BYTES 1,686,059,008
PHYSICAL_MEMORY_BYTES 51,539,607,552
NUM_CPUS 8
NUM_CPU_CORES 8
NUM_CPU_SOCKETS 8
GLOBAL_RECEIVE_SIZE_MAX 4,194,304
GLOBAL_SEND_SIZE_MAX 1,048,586
TCP_RECEIVE_SIZE_DEFAULT 87,380
TCP_RECEIVE_SIZE_MAX 4,194,304
TCP_RECEIVE_SIZE_MIN 4,096
TCP_SEND_SIZE_DEFAULT 16,384
TCP_SEND_SIZE_MAX 4,194,304
TCP_SEND_SIZE_MIN 4,096
Operating System Statistics -
Snap Time Load %busy %user %sys %idle %iowait
29-Feb 04:00:35 1.4 N/A N/A N/A N/A N/A
29-Feb 05:00:41 1.7 13.8 13.2 0.6 86.2 15.8
Foreground Wait Class
-> s - second, ms - millisecond - 1000th of a second
-> ordered by wait time desc, waits desc
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
-> Captured Time accounts for 97.6% of Total DB time 22,960.46 (s)
-> Total FG Wait Time: 18,651.75 (s) DB CPU time: 3,748.35 (s)
Avg
%Time Total Wait wait
Wait Class Waits -outs Time (s) (ms) %DB time
User I/O 3,327,253 0 18,576 6 80.9
DB CPU 3,748 16.3
Commit 23,882 0 69 3 0.3
System I/O 1,035 0 3 3 0.0
Network 842,393 0 2 0 0.0
Other 10,120 99 0 0 0.0
Configuration 3 0 0 58 0.0
Application 264 0 0 1 0.0
Concurrency 1,482 0 0 0 0.0
Foreground Wait Events
-> s - second, ms - millisecond - 1000th of a second
-> Only events with Total Wait Time (s) >= .001 are shown
-> ordered by wait time desc, waits desc (idle events last)
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
Avg
%Time Total Wait wait Waits % DB
Event Waits -outs Time (s) (ms) /txn time
db file sequential read 3,054,464 0 17,002 6 104.5 74.0
read by other session 199,603 0 796 4 6.8 3.5
direct path read 46,301 0 439 9 1.6 1.9
db file scattered read 21,113 0 269 13 0.7 1.2
log file sync 23,882 0 69 3 0.8 .3
db file parallel read 4,727 0 68 14 0.2 .3
control file sequential re 1,035 0 3 3 0.0 .0
SQL*Net message to client 840,792 0 2 0 28.8 .0
direct path read temp 95 0 2 18 0.0 .0
local write wait 79 0 0 4 0.0 .0
Disk file operations I/O 870 0 0 0 0.0 .0
ASM file metadata operatio 4 0 0 50 0.0 .0
log file switch (private s 3 0 0 58 0.0 .0
ADR block file read 36 0 0 3 0.0 .0
enq: RO - fast object reus 5 0 0 16 0.0 .0
latch: cache buffers chain 1,465 0 0 0 0.1 .0
SQL*Net break/reset to cli 256 0 0 0 0.0 .0
asynch descriptor resize 10,059 100 0 0 0.3 .0
SQL*Net more data to clien 1,510 0 0 0 0.1 .0
enq: KO - fast object chec 3 0 0 8 0.0 .0
SQL*Net more data from cli 91 0 0 0 0.0 .0
latch: shared pool 14 0 0 0 0.0 .0
ADR block file write 5 0 0 1 0.0 .0
reliable message 8 0 0 0 0.0 .0
direct path write temp 1 0 0 2 0.0 .0
SQL*Net message from clien 840,794 0 68,885 82 28.8
jobq slave wait 7,365 100 3,679 499 0.3
Streams AQ: waiting for me 721 100 3,605 5000 0.0
wait for unread message on 3,648 98 3,603 988 0.1
KSV master wait 20 0 0 0 0.0
Background Wait Events
-> ordered by wait time desc, waits desc (idle events last)
-> Only events with Total Wait Time (s) >= .001 are shown
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
Avg
%Time Total Wait wait Waits % bg
Event Waits -outs Time (s) (ms) /txn time
log file parallel write 29,353 0 83 3 1.0 34.8
db file parallel write 5,753 0 17 3 0.2 6.9
db file sequential read 1,638 0 15 9 0.1 6.1
control file sequential re 5,142 0 13 2 0.2 5.4
os thread startup 140 0 8 58 0.0 3.4
control file parallel writ 1,440 0 8 6 0.0 3.4
log file sequential read 304 0 8 26 0.0 3.3
db file scattered read 214 0 2 9 0.0 .8
ASM file metadata operatio 1,199 0 1 1 0.0 .3
direct path write 35 0 0 6 0.0 .1
direct path read 41 0 0 5 0.0 .1
kfk: async disk IO 6 0 0 9 0.0 .0
Disk file operations I/O 1,266 0 0 0 0.0 .0
ADR block file read 16 0 0 2 0.0 .0
read by other session 3 0 0 8 0.0 .0
Log archive I/O 2 0 0 10 0.0 .0
log file sync 3 0 0 5 0.0 .0
asynch descriptor resize 341 100 0 0 0.0 .0
CSS initialization 1 0 0 6 0.0 .0
log file single write 4 0 0 1 0.0 .0
latch: redo allocation 3 0 0 1 0.0 .0
ADR block file write 5 0 0 1 0.0 .0
LGWR wait for redo copy 45 0 0 0 0.0 .0
CSS operation: query 6 0 0 0 0.0 .0
CSS operation: action 1 0 0 1 0.0 .0
SQL*Net message to client 420 0 0 0 0.0 .0
rdbms ipc message 47,816 39 61,046 1277 1.6
DIAG idle wait 7,200 100 7,200 1000 0.2
Space Manager: slave idle 1,146 98 5,674 4951 0.0
class slave wait 284 0 3,983 14026 0.0
dispatcher timer 61 100 3,660 60006 0.0
Streams AQ: qmn coordinato 258 50 3,613 14003 0.0
Streams AQ: qmn slave idle 130 0 3,613 27789 0.0
Streams AQ: waiting for ti 7 71 3,608 515430 0.0
wait for unread message on 3,605 100 3,606 1000 0.1
pmon timer 1,201 100 3,604 3001 0.0
smon timer 15 73 3,603 240207 0.0
ASM background timer 754 0 3,602 4777 0.0
shared server idle wait 120 100 3,601 30006 0.0
SQL*Net message from clien 554 0 4 7 0.0
KSV master wait 101 0 0 2 0.0
Wait Event Histogram
-> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
-> % of Waits: value of .0 indicates value was <.05%; value of null is truly 0
-> % of Waits: column heading of <=1s is truly <1024ms, >1s is truly >=1024ms
-> Ordered by Event (idle events last)
% of Waits
Total
Event Waits <1ms <2ms <4ms <8ms <16ms <32ms <=1s >1s
ADR block file read 52 73.1 1.9 9.6 13.5 1.9
ADR block file write 10 100.0
ADR file lock 12 100.0
ARCH wait for archivelog l 3 100.0
ASM file metadata operatio 1203 97.3 .5 .7 .3 .2 .9
CSS initialization 1 100.0
CSS operation: action 1 100.0
CSS operation: query 6 83.3 16.7
Disk file operations I/O 2118 95.4 4.5 .1
LGWR wait for redo copy 45 100.0
Log archive I/O 2 100.0
SQL*Net break/reset to cli 256 99.6 .4
SQL*Net message to client 839.9 100.0 .0
SQL*Net more data from cli 91 100.0
SQL*Net more data to clien 1503 100.0
asynch descriptor resize 10.4K 100.0
buffer busy waits 2 100.0
control file parallel writ 1440 5.7 35.1 24.0 16.3 12.0 5.5 1.5
control file sequential re 6177 69.4 7.5 5.9 8.1 7.1 1.7 .3
db file parallel read 4727 1.7 3.2 3.2 10.1 46.6 33.3 1.8
db file parallel write 5755 42.3 21.3 18.6 11.2 4.6 1.4 .5
db file scattered read 21.5K 8.4 4.3 11.9 18.9 26.3 25.3 4.9
db file sequential read 3053. 28.7 15.1 11.1 17.9 21.5 5.4 .3 .0
direct path read 46.3K 9.9 8.8 18.5 21.7 22.8 15.7 2.7
direct path read temp 95 9.5 9.5 23.2 49.5 8.4
direct path write 35 11.4 31.4 17.1 22.9 11.4 2.9 2.9
direct path write temp 1 100.0
enq: KO - fast object chec 3 66.7 33.3
enq: RO - fast object reus 5 20.0 20.0 20.0 20.0 20.0
kfk: async disk IO 6 50.0 16.7 16.7 16.7
latch free 3 100.0
latch: cache buffers chain 1465 100.0
latch: cache buffers lru c 1 100.0
latch: object queue header 2 100.0
latch: redo allocation 3 33.3 33.3 33.3
latch: row cache objects 2 100.0
latch: shared pool 15 93.3 6.7
local write wait 79 35.4 34.2 21.5 8.9
log file parallel write 29.4K 47.8 21.7 11.9 9.9 6.8 1.6 .3
log file sequential read 304 6.3 3.0 3.6 10.2 23.4 24.3 29.3
log file single write 4 25.0 75.0
log file switch (private s 3 100.0
log file sync 23.9K 40.9 28.0 12.9 9.7 6.7 1.5 .3
os thread startup 140 100.0
read by other session 199.6 37.1 19.9 12.9 13.1 13.8 3.1 .2
reliable message 8 100.0
ASM background timer 755 2.9 .4 .1 .1 .3 .1 .3 95.8
DIAG idle wait 7196 100.0
KSV master wait 121 88.4 2.5 3.3 2.5 .8 .8 1.7
SQL*Net message from clien 840.1 97.1 1.8 .5 .2 .2 .1 .0 .1
Space Manager: slave idle 1147 .1 .5 99.4
Streams AQ: qmn coordinato 258 49.6 .4 50.0
Streams AQ: qmn slave idle 130 .8 99.2
Streams AQ: waiting for me 721 100.0
Streams AQ: waiting for ti 7 28.6 42.9 28.6
class slave wait 283 39.9 2.5 2.5 3.5 4.9 9.2 15.2 22.3
dispatcher timer 60 100.0
jobq slave wait 7360 .0 .0 .0 99.9
pmon timer 1201 100.0
rdbms ipc message 47.8K 2.7 31.6 17.4 1.1 1.1 .9 20.9 24.3
Wait Event Histogram DB/Inst: I2KPROD/I2KPROD Snaps: 5606-5607
-> Units for Total Waits column: K is 1000, M is 1000000, G is 1000000000
-> % of Waits: value of .0 indicates value was <.05%; value of null is truly 0
-> % of Waits: column heading of <=1s is truly <1024ms, >1s is truly >=1024ms
-> Ordered by Event (idle events last)
% of Waits
Total
Event Waits <1ms <2ms <4ms <8ms <16ms <32ms <=1s >1s
shared server idle wait 120 100.0
smon timer 16 6.3 93.8
wait for unread message on 7250 .1 99.9
Latch Miss Sources
-> only latches with sleeps are shown
-> ordered by name, sleeps desc
NoWait Waiter
Latch Name Where Misses Sleeps Sleeps
In memory undo latch ktichg: child 0 1 0
active service list kswslogon: session logout 0 2 0
cache buffers chains kcbgtcr_2 0 1,123 483
cache buffers chains kcbgtcr: fast path (cr pin 0 496 1,131
cache buffers chains kcbrls_2 0 5 6
cache buffers chains kcbgcur_2 0 4 0
cache buffers chains kcbgtcr: fast path 0 3 1
cache buffers chains kcbzwb 0 2 4
cache buffers chains kcbchg1: kslbegin: bufs no 0 1 0
cache buffers chains kcbnew: new latch again 0 1 0
cache buffers chains kcbrls_1 0 1 6
cache buffers chains kcbzgb: scan from tail. no 0 1 0
cache buffers lru chain kcbzgws 0 1 0
object queue header oper kcbo_switch_cq 0 1 0
object queue header oper kcbo_switch_mq_bg 0 1 2
redo allocation kcrfw_redo_gen: redo alloc 0 3 0
row cache objects kqrpre: find obj 0 1 1
row cache objects kqrso 0 1 0
shared pool kghalo 0 13 3
shared pool kghupr1 0 4 15
shared pool kghalp 0 1 0
space background task la ktsj_grab_task 0 2 2
------------------------------------------------------------- -
Hi
Please help. The situation is that we found the Read By Other Sessions Event occurs and the sessions hang for a week. No new Sessions ID suffers from ths events and Just keep 10 Sessions ID with this event waiting. Our user didn't suffer any performance problem so far.
Our Application layer is Web-based, I believe users related to those sessions are disconnected already. So How come those session ID waits so long !!!!
Thx
KitOur DBA helped me to get the information from the V$Session. Let Session ID = 123. We found that this session has Read by Other Session" event from 17-May up to now every 10 seconds.
DBA gives me the following fields to study
Time
INSTANCE_NUMBER
SESSION_ID
DB User
EVENT_NAME
CURRENT_OBJ#
CURRENT_FILE#
CURRENT_BLOCK#
SEQ#
EVENT_ID P1 P2 P3
WAIT_TIME TIME_WAITED SQL_ID SQL_TEXT -
Difference between wait event and timed event
Hi,
Anyone has idea that what is the difference between wait events and timed events in Statspack report. I couldn't find it over google.
Thanks.It's 10.2.0.1 on Linux
(Couldn't do a query, because Linux is inside VM Ware. And it is not being accessed from Base windows machine.)
Top 5 Timed Events Avg %Total
~~~~~~~~~~~~~~~~~~ wait Call
Event Waits Time (s) (ms) Time
db file scattered read 9,750,617 34,611 4 44.7
CPU time 14,248 18.4
read by other session 1,532,282 8,984 6 11.6
db file sequential read 4,514,494 5,588 1 7.2
latch: cache buffers lru chain 277,245 4,823 17 6.2
Wait Events DB/Inst: ABCD/ABCD Snaps: 1-2
-> s - second, cs - centisecond, ms - millisecond, us - microsecond
-> %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0
-> Only events with Total Wait Time (s) >= .001 are shown
-> ordered by Total Wait Time desc, Waits desc (idle events last)
Avg
%Time Total Wait wait Waits
Event Waits -outs Time (s) (ms) /txn
db file scattered read 9,750,617 0 34,611 4 24.2
read by other session 1,532,282 0 8,984 6 3.8
db file sequential read 4,514,494 0 5,588 1 11.2
latch: cache buffers lru chain 277,245 0 4,823 17 0.7
latch free 121,466 0 3,291 27 0.3
---------------------------------------------------------------------------------------------------- -
Hello SAP Community,
I start by mentioning a few details about the system I'll be talking about in this subject:
- SAP NetWeaver 7.0
- Oracle Database 10.2g
I was reading the following Note: "Note 618868 - FAQ: Oracle performance", in order to try to understand what's causing the oracle database to have slow performance.
While reading section 3 "How can I determine whether the general database performance can be optimized?" I found out that the ratio of "Busy wait time to CPU time" is away above the recommended 60:40 value. I'm getting a 94:6 ratio. This value was calculated using the query:
SELECT
ROUND((STM1.VALUE - STM2.VALUE) / 1000000) "BUSY WAIT TIME (S)",
ROUND(STM2.VALUE / 1000000) "CPU TIME (S)",
ROUND((STM1.VALUE - STM2.VALUE) / STM1.VALUE * 100) || ' : ' ||
ROUND(STM2.VALUE / STM1.VALUE * 100) RATIO
FROM V$SYS_TIME_MODEL STM1, V$SYS_TIME_MODEL STM2
WHERE STM1.STAT_NAME = 'DB time' AND STM2.STAT_NAME = 'DB CPU';
With such high values, SAP recommends to improve system performance doing some "wait event tuning".
Can someone give me some directions about this subject? Some guides specific to this subject would be nice. Any further information about my system you may require, please ask me.
Thanks in advance.
Best regards,
Daniel GarridoHello again,
Before I did any changes to the Oracle's parameters I checked the Note 619188 - FAQ: Oracle wait events, to understand what could be causing such high event wait time.
With the query:
SELECT EVENT, TOTAL_WAITS, TIME_WAITED, AVG_MS,
ROUND(RATIO_TO_REPORT(TIME_WAITED) OVER () * 100) PERCENT
FROM (SELECT SUBSTR(EVENT, 1, 30) EVENT, TOTAL_WAITS, TIME_WAITED,
ROUND(TIME_WAITED_MICRO / TOTAL_WAITS / 1000, 2) AVG_MS
FROM V$SYSTEM_EVENT
WHERE WAIT_CLASS NOT IN ('Idle', 'System I/O')
UNION
SELECT 'CPU' EVENT, NULL, VALUE, NULL
FROM V$SYSSTAT
WHERE STATISTIC# = 12
ORDER BY 3 DESC)
WHERE ROWNUM <=10;
I got the non-idle events that took more time in my system and the result was:
Result of the SELECT statement
EVENT
TOTAL_WAITS
TIME_WAITED
AVG_MS
PERCENT
log file switch (archiving nee
578.686
57.850.863
999.69
80
buffer busy waits
712.163
6.420.932
90.16
9
CPU
0
2.791.238
4
db file sequential read
4.005.546
1.746.442
4.36
2
log file sync
10.176.490
1.577.177
1.55
2
enq: TX - row lock contention
854.451
642.955
7.52
1
db file scattered read
1.055.533
621.332
5.89
1
enq: CF - contention
210.085
246.910
11.75
0
read by other session
561.558
119.910
2.14
0
log file switch completion
10.777
85.843
79.65
0
So most of the TIME_WAITED for wait events was because of the "log file switch (archiving needed)", after reading what could cause such wait event, I understood this was related with a problem I previously had in the server, where the archiving folder was with no space left. (Meanwhile the backup of the archives is being done and so the folder is being cleaned on a daily basis).
Thank you all for your help! -
( name-service call wait ) event is amoung the top 5 wait events
10.2.0.3 2node- RAC
When I check the wait event in the active session wait event the sessions can be see that they are blocked by the LMON process. The wait event appears only on one node.
It is very hard to find information on the net or on the metalink.
How could I overcome this wait event ?
select program, type from v$session
where sid in
(select blocking_session from v$active_session_history
where event like 'name-service%'
and rownum < 1000 )
oracle@dbokyanus1 (LMON) , BACKGROUND
Top 5 Timed Events Avg %Total
~~~~~~~~~~~~~~~~~~ wait Call
Event Waits Time (s) (ms) Time
db file sequential read 4,331,507 15,218 *4* *31.2*
CPU time *8* *17.5*
log file sync 1,462,968 5,513 *4* *11.3*
name-service call wait 72,058 4,545 *63* *9.3*
SQL*Net message from dblink 4,197 4,047 *964* *8.3*oceanic-815 wrote:
10.2.0.3 2node- RAC
When I check the wait event in the active session wait event the sessions can be see that they are blocked by the LMON process. The wait event appears only on one node.
It is very hard to find information on the net or on the metalink.
If I use Google to find information about this
I ran into this page.
There is indeed not much to find about this wait-event, other than there is probably some sort of network communication problem between the two nodes.
Maybe the best solution is to raise a S/R at Oracle support -
RAC 10.2.0.5 - Session waiting forever
Hi, i feel alone
The database has several sessions that are waiting forvever.
Sometimes these sessions are wainting for "direct path read", or "read by other session"
The objects on which the sessions are waiting are never the same (user table, or LOB, ...)
The OS process associated with the database session doesn't exists anymore on the system.
The connection is made with JDBC THIN CLIENT.
NO error messages as the session is just waiting indefinitly
If a start a new session and issue a simple SQL SELECT on the waited objects on both instance.
The first instance return the resultset. The second instance just wait forever.
After the blocked objects is rebuilt, SQL SELECT works fine from both instance.
Killing the waiting sessions doesn't solve the probleme as next same SQL QUERY from the other instance, will be blocked too ...
Rebuild the object solve the problem ...
BUT THIS IS FAR NOT A GOOD SOLUTION !
The database is Oracle 10.2.0.5 SE RAC for LInux RHEL5 x64.
ASM is used.
Thank you for any suggestions !Hi,
thank you for your response.
This is a STANDARD EDITION with all tables degree set to 1, and all indexes degrees set to 1 or 0.
I kill the session selected with the following query (the ones with high last_call_et)
select inst_id, username, last_call_et, event, row_wait_obj# from gv$session where status='ACTIVE' and state='WAITING' and username is not null;
Sometime, just kill the session solve the problem
Now, i got 1 session waiting forever on "read by other session" on table SYSTEM.SQLPLUS_PRODUCT_PROFILE the SQL executed is
"analyze table infomed2.dm_ligne ....;" .
The same problem appears on 2 differents databases on the same RAC cluster (all in 10.2.0.5)
i guess a bug with dictionnary latch, or with gcs, or with sqlnet( session closed but not realeased), ... but cannot find any information -
What's wrong from this wait event
Please,
Below are two tables showing respectively database wait event by wait class and session wait event by wait class.
1. Database wait event by wait class
WAIT TOTAL PCT TIME PCT
CLASS WAITS WAITS WAITED_SECS TIME
Application 7427 .08 1572.45 76.29
User I/O 50416 .57 193.24 9.38
Network 8714874 98.66 177.67 8.62
System I/O 48169 .55 85.98 4.17
2. Session wait event by wait class
SID USER WAIT TOTAL TIME_
NAME CLASS WAITS WAITED_SECS
318 PMS1000 Application 110 321.64
259 PMS1000 Application 81 212.8
318 PMS1000 Network 541943 31.8
259 PMS1000 Network 258368 17.76
258 PMS1000 Network 132774 9.34
318 PMS1000 User I/O 1392 7.49
Top Events found:
CPU + WAIT for CPU
ROW lock contention
SQL*Net more data from/to client
Question:
What may cause the application wait_class to be at the top?, event though the row lock contention was found ?
I also think the system may sufering from a network bottleneck, I also thinking to set SDU parameter, but the network is 1Gb speed, and I don't know if this can help.
Does someone give me some clue to pinpoint what is going wrong wiht the above stats?
thanks enoughuser552326
I've used the "code" tags to make your first section of data more readable:
WAIT TOTAL PCT TIME PCT
CLASS WAITS WAITS WAITED_SECS TIME
Application 7427 .08 1572.45 76.29
User I/O 50416 .57 193.24 9.38
Network 8714874 98.66 177.67 8.62
System I/O 48169 .55 85.98 4.17 If you want to know what events belong to each wait class you can query v$event_name:
select wait_class, name
from v$event_name
order by wait_class, nameThe events in class "Application" are:
SQL*Net break/reset to client
SQL*Net break/reset to dblink
Streams capture: filter callback waiting for ruleset
Streams: apply reader waiting for DDL to apply
Wait for Table Lock
enq: KO - fast object checkpoint
enq: PW - flush prewarm buffers
enq: RO - contention
enq: RO - fast object reuse
enq: TM - contention
enq: TX - row lock contention
enq: UL - contention
As you can see, this is consistent with your comment about the top event being "row lock contention". The implication of the name given to this wait class is that it is your application design that is causing the problem. Your biggest problem is that your code allows your users to lock each other out.
Looking at the summary numbers, the time spent on waiting for other users to get out of the way is a very large fraction of your total wait - until you deal with that, problems relating to I/O and network appear to be pretty irrelevant. Having said that, you seem to do a very large number of round-trips on the network - so maybe the amount of time you are losing is not hugely significant compared to the amount of work you are getting done. (You didn't actually tell us how long it took or how many concurrent users, to accumulate this wait time).
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk -
My wait events - can anyone see a problem?
hi,
this is what i have, can anyone see a problem?
thanks
EVENT TOTAL_WAITS PCT_WAITS TIME_WAIT_SEC PCT_TIME_WAITED TOTAL_TIMEOUTS PCT_TIMEOUTS AVERAGE_WAIT_SEC
Streams AQ: qmn slave idle wait 148147 .3 4051461.88 38.04 3478 .07 27.35
Streams AQ: qmn coordinator idle wa 291006 .59 3962890.53 37.21 148370 3.13 13.62
it
Streams AQ: waiting for time manage 948 0 2021434.2 18.98 948 .02 2132.31
ment or cleanup tasks
control file parallel write 1292057 2.64 266839.64 2.51 0 0 .21
log file parallel write 28433394 58.02 134658.55 1.26 0 0 0
db file sequential read 8307195 16.95 69830.07 .66 0 0 .01
free buffer waits 3117839 6.36 43374.04 .41 3106093 65.55 .01
log buffer space 55520 .11 20810.2 .2 20235 .43 .37
db file scattered read 583604 1.19 18169.58 .17 0 0 .03
write complete waits 17946 .04 17536.66 .16 17941 .38 .98
log file sync 282268 .58 10005.35 .09 9369 .2 .04
enq: RO - fast object reuse 26602 .05 6623.44 .06 2171 .05 .25
enq: CF - contention 1839 0 5178.14 .05 1723 .04 2.82
Streams AQ: qmn coordinator waiting 999 0 4311.01 .04 883 .02 4.32
for slave to start
buffer busy waits 32464 .07 3898.51 .04 3950 .08 .12
control file sequential read 2199199 4.49 3558.34 .03 0 0 0
SGA: MMAN sleep for component shrin 234330 .48 2523.65 .02 234216 4.94 .01
k
buffer exterminate 1583 0 1539.72 .01 1573 .03 .97
library cache pin 317 0 927.71 .01 316 .01 2.93
enq: CI - contention 1829 0 570.84 .01 159 0 .31
log file switch completion 1658 0 517.18 0 425 .01 .31
enq: TX - row lock contention 257 0 438.8 0 149 0 1.71
read by other session 27269 .06 355.17 0 52 0 .01
os thread startup 3869 .01 338.67 0 98 0 .09
latch: shared pool 760 0 285.87 0 0 0 .38
latch: row cache objects 664 0 250 0 0 0 .38
Data file init write 16324 .03 231.59 0 0 0 .01
reliable message 19189 .04 218.16 0 170 0 .01
latch: library cache 483 0 172.51 0 0 0 .36
SQL*Net message from dblink 1143086 2.33 128.69 0 0 0 0
latch free 6091 .01 121.1 0 0 0 .02
library cache load lock 90 0 89.48 0 18 0 .99
log file single write 1894 0 69.76 0 0 0 .04
cursor: pin S wait on X 5183 .01 55.87 0 5165 .11 .01
local write wait 6732 .01 42.58 0 2 0 .01
log file switch (checkpoint incompl 95 0 42.11 0 30 0 .44
ete)
row cache lock 119 0 30.96 0 10 0 .26
SQL*Net more data from dblink 17198 .04 25.92 0 0 0 0
log file switch (private strand flu 69 0 17.54 0 5 0 .25
sh incomplete)
enq: HW - contention 180 0 16.53 0 5 0 .09
enq: PR - contention 9 0 14.5 0 2 0 1.61
enq: JS - queue lock 51 0 12.36 0 0 0 .24
SQL*Net more data to client 48311 .1 11.66 0 0 0 0
enq: TM - contention 12 0 10.66 0 3 0 .89
class slave wait 3128 .01 7.03 0 1 0 0
JS coord start wait 68 0 6.42 0 68 0 .09
direct path write 92712 .19 6.06 0 0 0 0
control file heartbeat 1 0 3.91 0 1 0 3.91
PX Deq: Par Recov Execute 100 0 3.8 0 0 0 .04
log file sequential read 1900 0 2.88 0 0 0 0
single-task message 50 0 2.61 0 0 0 .05
enq: TX - contention 11 0 2.38 0 0 0 .22
undo segment extension 1181001 2.41 1.95 0 1180981 24.92 0
db file single write 165 0 1.3 0 0 0 .01
enq: TX - index contention 97 0 1.27 0 0 0 .01
LGWR wait for redo copy 20840 .04 .66 0 0 0 0
JS kgl get object wait 8 0 .63 0 8 0 .08
SQL*Net message to dblink 1143086 2.33 .55 0 0 0 0
kksfbc child completion 14 0 .55 0 11 0 .04
direct path read temp 217237 .44 .41 0 0 0 0
latch: cache buffers chains 2138 0 .37 0 0 0 0
latch: messages 1245 0 .27 0 0 0 0
latch: redo writing 786 0 .15 0 0 0 0
PX Deq: Par Recov Reply 65 0 .09 0 0 0 0
latch: checkpoint queue latch 171 0 .09 0 0 0 0
latch: redo allocation 1029 0 .08 0 0 0 0
latch: cache buffers lru chain 268 0 .07 0 0 0 0
SGA: allocation forcing component g 5 0 .05 0 2 0 .01
rowth
db file parallel read 83 0 .04 0 0 0 0
latch: In memory undo latch 558 0 .04 0 0 0 0
latch: object queue header operatio 338 0 .04 0 0 0 0
n
direct path read 5042 .01 .03 0 0 0 0
PX Deque wait 7 0 .02 0 0 0 0
direct path write temp 4691 .01 .02 0 0 0 0
enq: SQ - contention 1 0 .02 0 0 0 .02
latch: session allocation 190 0 .02 0 0 0 0
PX Deq: Join ACK 15 0 .01 0 0 0 0
cursor: pin S 894 0 .01 0 0 0 0
enq: TX - allocate ITL entry 37 0 .01 0 0 0 0
kkdlgon 15 0 .01 0 0 0 0
latch: enqueue hash chains 37 0 .01 0 0 0 0
library cache lock 1 0 .01 0 0 0 .01
Log archive I/O 1 0 0 0 0 0 0
PX Deq: Par Recov Change Vector 2 0 0 0 0 0 0
PX Deq: Signal ACK 3 0 0 0 0 0 0
PX Deq: Test for msg 1 0 0 0 0 0 0
PX qref latch 1 0 0 0 1 0 0
SQL*Net break/reset to dblink 5 0 0 0 0 0 0
SQL*Net more data to dblink 1 0 0 0 0 0 0
buffer deadlock 27 0 0 0 27 0 0
checkpoint completed 4 0 0 0 0 0 0
cursor: mutex S 3 0 0 0 0 0 0
cursor: mutex X 1 0 0 0 0 0 0
enq: JS - q mem clnup lck 1 0 0 0 0 0 0
enq: PS - contention 2 0 0 0 0 0 0
enq: US - contention 1 0 0 0 0 0 0
instance state change 2 0 0 0 0 0 0
latch: library cache lock 4 0 0 0 0 0 0
latch: library cache pin 1 0 0 0 0 0 0
latch: object queue header heap 8 0 0 0 0 0 0
latch: undo global data 3 0 0 0 0 0 0
recovery read 39 0 0 0 0 0 0Hi,
If its for a week than I won't bother. Probably you should try to get teh same report for these wait events in a much smaller period , like 20-30minutes of time period when your db is fully operational. If still at that time the wait events,these or any other, shoot up to high wait times, things can be investigated more deeply.
HTH
Aman.... -
High waits on scatter read and buffer busy wait ..
one of my system is undergoing some serious problem ~
i checked when some sql querying few large tables ( 30 millions rows ,partioned )
system waits became significant .. the ones stand out are scatter read and buffer busy wait ...
on the longop , you can see those sessions waitting to scan the large table ..
buffer get ratio dropped from 90% to like 30% ,average buffer hit ratio is like 55%
mu questions are
1.what's your view of throwing the problem away ?
add physical memory, then increase data buffer ?
it's getting scanned very often , but it's too large to pin it in the keep pool .
2. why buffer busy wait ?
i don't fully understand why this happened ?
becase what they are doing are just querying ,nobody is modifing any data ?
will increase freelist help this ??
thanks your talneted ideas
br/rickyHave these SQL statements been added recently, or have they been around for a long time. If the latter, then it seems likely that they've changed their execution plan to start doing tablescans (hence db file scattered read waits) or index fast full scans.
One of the causes of buffer busy waits is concurrent tablescans/index fast full scans - in 10g this particular cause has been split and reported as "read by other session".
Your first action should be to see if there is a more efficient execution plan for these queries. If the problem is due to a change in execution plan, common causes are: changes in statistics on the objects, failure to change statistics on the objects, changes in input value on the queries, changes in optimizer parameters, unlucky changes in data volumes.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk -
Lot of sessions with wait event - jobq slave wait
Hi All,
My db version is 10.2.0.4.0
I have scheduled jobs through dbms_scheduler with repeat_interval of 20 mins(this for refresh of mviews).
Now the job is in running state for a long time. then i checked the sessions..
I have five session with wait event - "jobq slave wait"
I check job_queue_parameter - 10
select count(1) from dba_jobs;
COUNT(1)
8
Now the job is in running state for a long time...
Can someone help me how to proceed...
Thanks,
Suresh S.Post Operating System (OS) name & version for DB server system.
Post results of
SELECT * from v$version
does following SQL return any rows? If so, they point to problem area.
SELECT DECODE(request,0,'Holder: ','Waiter: ')||sid sess,
id1, id2, lmode, request, type
FROM V$LOCK
WHERE (id1, id2, type) IN
(SELECT id1, id2, type FROM V$LOCK WHERE request>0)
ORDER BY id1, request
/ -
Latch: session allocation in top 5 wait events
Hi,
This wait event session is coming in the top 5 timed events
How to proceed for solving this issue?
This database is only being used for migration activities currently,which means a lot of imports going on.
PFB the Top 5 Timed Foreground Events
++++++++++++++++++
Event Waits Time(s) Avg wait (ms) % DB time Wait Class
DB CPU 8,437 57.95
latch: session allocation 2,035,326 3,671 2 25.22 Other
wait list latch free 243,511 2,448 10 16.81 Other
direct path write 504,262 363 1 2.49 User I/O
log file sync 39,396 156 4 1.07 Commit
++++++++++++++++++
Cheers,
Kunwaruser9131570 wrote:
This database is only being used for migration activities currently,which means a lot of imports going on.
PFB the Top 5 Timed Foreground Events
++++++++++++++++++
Event Waits Time(s) Avg wait (ms) % DB time Wait Class
DB CPU 8,437 57.95
latch: session allocation 2,035,326 3,671 2 25.22 Other
wait list latch free 243,511 2,448 10 16.81 Other
direct path write 504,262 363 1 2.49 User I/O
log file sync 39,396 156 4 1.07 Commit
++++++++++++++++++
A little more information would help - you could start with the Load Profile section, and the summary of the number of sessions, CPU, and memory. Also OSSTATs might be helpful and the Time Model stats. The version of Oracle might also be relevant.
See the note below about using the "code" tag and preview option.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.
There is a +"Preview"+ tab at the top of the text entry panel. Use this to check what your message will look like before you post the message. If it looks a complete mess you're unlikely to get a response. (Click on the +"Plain text"+ tab if you want to edit the text to tidy it up.)
+"Science is more than a body of knowledge; it is a way of thinking"+
+Carl Sagan+ -
Wait Event Direct path read TEMP
HI,
I have two sessions waiting on wait event "DIECT PATH READ TEMP" (both the sessions with same SQL).Those sessions are almost in hung state.If i run that query from any other session,even that gets hanged.I have generated 10046 trace for these and found that all of them are waiting for a index object in TEMP datafile.
Has anyone of you had the same issue.
Please explain me what kind of action i have taken.
I have verified the stats..they are all up to date.
Thanks,
Pramod GarreHi ,
It is IMPOSSIBLE for two SELECT statements to obstruct each other.-
Its not impossible my dear.Do you know something called "Hot Block".Dont you know that in that case select queries obstruct each other??Dont suggest if you dont know.
If you don't post meaningful information, you'll be left with your own mystery-
I agree i have to provide more information.
Thanks
Pramod
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