Explain Plan guide

Hi ALL,
I wanted to know how to use explain plan in detail,Can any one please sujext me good link for this?
Regards
Raghavendra Nara

Oracle® Database 2 Day + Performance Tuning Guide:
http://download.oracle.com/docs/cd/B19306_01/server.102/b28051/toc.htm
Oracle® Database Performance Tuning Guide:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/toc.htm
'Compact version':
http://www.akadia.com/services/ora_interpreting_explain_plan.html

Similar Messages

Query tunning in Oracle using Explain Plan

Adding to my below question: I have now modified the query and the path shownby 'Explain plan' has reduced. The 'Time' column of plan_table is also showing much lesser value. However, some people are suggesting me to consider the time required by the query to execute on Toad. Will it be practical? Please help!!
Hi, I am using Oracle 11g. I need to optimize a Select query(Need to minimize the execution time). I need to know how 'Explain Plan' would help me. I know how to use Explain Plan command. I refer Plan_table table to see the details of the plan. Please guide me regarding which columns of the Plan_table should be considered while modifying the query for optimization. Some people say, 'Time' column should be considered, some say 'Bytes' etc. Some suggest on minimizing the full table scans, while some people say that I should minimize the total no. operations (less no. of rows should be displayed in Plan_table). As per an experienced friend of mine, full table scans should be reduced (for e.g. if there are 5 full table scans in the plan, then try to reduce them to less than 5. ). However, if I consider any full table scan operation in the plan_table, its shows value of 'time' column as only 1 which is very very less. Does this mean the full scan is actually taking very less time?? If yes, then this means full table scans are very fast in my case and no need to work on them. Some articles suggest that plan shown by 'Explain Plan' command is not necessarily followed while executing the query. So what should I look for then? How should I optimize the query and how will I come to know that it's optimized?? Please help!!...
Edited by: 885901 on Sep 20, 2011 2:10 AM

885901 wrote:
Hi, I am using Oracle 11g. I need to optimize a Select query(Need to minimize the execution time). I need to know how 'Explain Plan' would help me. I know how to use Explain Plan command. I refer Plan_table table to see the details of the plan. Please guide me regarding which columns of the Plan_table should be considered while modifying the query for optimization. Some people say, 'Time' column should be considered, some say 'Bytes' etc. Some suggest on minimizing the full table scans, while some people say that I should minimize the total no. operations (less no. of rows should be displayed in Plan_table). As per an experienced friend of mine, full table scans should be reduced (for e.g. if there are 5 full table scans in the plan, then try to reduce them to less than 5. ). However, if I consider any full table scan operation in the plan_table, its shows value of 'time' column as only 1 which is very very less. Does this mean the full scan is actually taking very less time?? If yes, then this means full table scans are very fast in my case and no need to work on them. Some articles suggest that plan shown by 'Explain Plan' command is not necessarily followed while executing the query. So what should I look for then? How should I optimize the query and how will I come to know that it's optimized?? Please help!!...how fast is fast enough?

Tunning using EXPLAIN PLAN

HI,
I am trying to do EXPLAIN PLAN. But SP HAS SO MANY PARAMETER declaration, its very difficult to run explain for each select statement.
Can any one help me how to run explain paln.

885901 wrote:
Hi, I am using Oracle 11g. I need to optimize a Select query(Need to minimize the execution time). I need to know how 'Explain Plan' would help me. I know how to use Explain Plan command. I refer Plan_table table to see the details of the plan. Please guide me regarding which columns of the Plan_table should be considered while modifying the query for optimization. Some people say, 'Time' column should be considered, some say 'Bytes' etc. Some suggest on minimizing the full table scans, while some people say that I should minimize the total no. operations (less no. of rows should be displayed in Plan_table). As per an experienced friend of mine, full table scans should be reduced (for e.g. if there are 5 full table scans in the plan, then try to reduce them to less than 5. ). However, if I consider any full table scan operation in the plan_table, its shows value of 'time' column as only 1 which is very very less. Does this mean the full scan is actually taking very less time?? If yes, then this means full table scans are very fast in my case and no need to work on them. Some articles suggest that plan shown by 'Explain Plan' command is not necessarily followed while executing the query. So what should I look for then? How should I optimize the query and how will I come to know that it's optimized?? Please help!!...how fast is fast enough?

Understand an explain plan

Hi,
following is the explain plan for my query :
Plan Table
| Operation                 | Name              | Rows | Bytes| Cost | Pstart| Pstop |
| SELECT STATEMENT          |                    |     1 | 139 |    464 |       |       |
| SORT GROUP BY            |                    |     1 | 139 |    464 |       |       |
|   NESTED LOOPS            |                    |     1 | 139 |    453 |       |       |
|    HASH JOIN              |                    |   352 |   35K|    277 |       |       |
|     NESTED LOOPS          |                    |   105 |    7K|     54 |       |       |
|      TABLE ACCESS BY INDEX|PS_CE_ITEMVAR_TMP   |   101 |    5K|     53 |       |       |
|       INDEX RANGE SCAN    |PS_C_ITEMVAR_TMP    |   101 |      |      5 |       |       |
|      INDEX UNIQUE SCAN    |PS_ITEMS_INV        |    14K| 244K|        |       |       |
|     TABLE ACCESS FULL     |PS_OUTPUT_LIST      |    47K|    1M|    222 |       |       |
Plan Table
|    TABLE ACCESS BY INDEX R|PS_SF_PRDNID_HEADR |    31K|    1M|      1 |       |       |
|     INDEX UNIQUE SCAN     |PS_SF_PRDNID_HEADR |    31K|      |        |       |       |
------------------------------------------------------------------------------------------How to understand it ? How to interpret it ?
Does this explain plan suggest you any tuning or any idea ?
Many thanks.

Can you check if you can avoid full table scan of this table - PS_OUTPUT_LIST
How to understand it ? How to interpret it ?Here is the rule.
1) First goto the inner most line. That will be the first one to get executed/accessed
Note : If two are two lines that are the same innermost level, then the one that is above it will get accessed first.
Here is the order for your case in sequence
1) INDEX RANGE SCAN |PS_C_ITEMVAR_TMP
2) TABLE ACCESS BY INDEX|PS_CE_ITEMVAR_TMP (a)
3) INDEX UNIQUE SCAN - PS_ITEMS_INV (b)
4) a and b will be joined to form a rowset - (c)
5) TABLE ACCESS FULL |PS_OUTPUT_LIST - (d)
6) c and d will have NESTED LOOPS ..
So on...
Please read the 9i or 10g Performance Tuning guide - that has the same explanation in the initial chapters
Message was edited by:
Srinivas.R

Explain plan changes by result size from contains clause

I use 10.2.0.3 Std Edition and have a query like this
select t1.id from table1 t1
where t1.col99 = 123
and t1.id in (select ttxt.id from fulltexttable ttxt where contains (ttxt.thetext, 'word1 & word2'));
(note: for each row in table1 exists at least one corresponding row in fulltexttable)
Now I came across a surprising change in execution plans depending on the values of word1 and word2:
- if the number of result rows from the subquery is low compared to all rows the full text index is used (table access by rowid/domain index)
- if the number of result rows is high explain plan does not indicate any use of the domain index (full text index) but only a full text table scan. And the slow execution proves this plan.
But: if I create explain plan for the subquery only there is no difference whether the number of result rows is high or low: the full text index is always used.
Any clue for this change in execution strategy?
Michael

hi michael,
this is expected behaviour. because you have a query incorporating more than just a text-index, and furthermore, multiple tables, the optimizer may choose different access paths according to the cardinality of your where clause terms. in fact, anything you see is actually vanilla behaviour.
however, as i suppose, you probably have not yet heard about the "post filter" characteristic of a context index. see the tuning chapter of the text dev guide for more info. also note that the optimizer has no other way than accessing the context index directly iff you execute the subquery on its own (the "post filter" characteristic is not applicable here, because a post filter always needs some input to be filtered). and finally, be aware that oracle may unnest your subquery by its own decision, that is, do not try to force a direct context index access by a subquery, it will not work (a compiler hint is the only thing that works relyably).
the only thing i can not follow is the fts for your second example. dont you have join indexes on table1.id and fulltexttable.id, respectively?
p

Explain Plan for Procedure

Hi,
For getting the explain plan for a query, we use the statement
"explain plan for " + Query
Similarly, to get an explain plan for a procedure, do we have any way like
"explain plan for " + "Execute " + Procedure
How do we get an explain plan for a procedure that is executed
Thanks in Advance.

teckfreak wrote:
Hi Robert,
I am working on an utility application which will execute the procedure and show the explain plan to the user for him to analyze the explain plan and take necessary steps for optimization. I am showing the Procedure inputs to the user, allowing him to enter values and taking them and executing the procedure. I am setting the trace and extracting the explain plan for the procedure using TKPROF utility and showing it to the user.
While doing so, the trace file is stored in udump folder. I am accessing the trace file from TKPROF utility. I am able to run the TKPROF from the command prompt. But if I try automating the TKPROF command in a .NET application using Process.Start, it says "Not able to access the file.". I tried giving full permissions to Everyone and it still throws the error. Kindly guide me how to proceed.. A different approach that you might want to consider (as indicated by William):
- Flush the shared pool and use a unique MODULE description for each execution of your procedure (e.g. using DBMS_APPLICATION_INFO.SET_MODULE), e.g. using a logon trigger
- Query V$SQL for your unique MODULE description and run DBMS_XPLAN.DISPLAY_CURSOR for each corresponding child cursor found (SQL_ID + CHILD_NUMBER) in the shared pool. This plan generation could be automated using a procedure
The result of this approach corresponds to the tracing using TKPROF since it will provide the actual execution plans used at runtime rather than separate EXPLAIN PLAN results which might differ from the actual plans.
This assumes that your shared pool is sufficiently large to hold all the child cursor created by your procedure without aging them out while the procedure is running. It's probably also only applicable to an environment where not too much work is being done while running this test and the recommended flushing of the shared pool.
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/

Query with Explain Plan

Suppose, i am using two queries [ which are almost equal] but using separate table name aliases. Will this result is separate Explain Plans?
i.e.
Explain Plan for : Select * from emp a;
and Explain for : Select * from emp b;
Will remain same always, or it will differ?
Also, i was looking for low level conversion of Parsed SQL statements to Machine Level Language. I mean how this step is performed. Where does the compiler/interpreter resides and how it works.
Thanks in Advance.
Regards,
Sudipta.

user13513014 wrote:
Suppose, i am using two queries [ which are almost equal] but using separate table name aliases. Will this result is separate Explain Plans?
i.e.
Explain Plan for : Select * from emp a;
and Explain for : Select * from emp b;
Will remain same always, or it will differ? By simply switching alias, the optimizer is unlikely to develop a new plan.
Also, i was looking for low level conversion of Parsed SQL statements to Machine Level Language. I mean how this step is performed. Where does the compiler/interpreter resides and how it works.
Thanks in Advance.
Regards,
Sudipta.There is no way you can actally see the parsing of SQL. It is done internally by oracle in a process caled Hard Parse or Soft Parse. A Hard Parse is where the optimizer must go through all the steps of parsing from the beggining, where as a soft parse, oracle uses the cached results from a hard parsed query that is in the shared pool.
How the optimizer works is a subject of ample documentation and several books. As a general over view, here are the general steps at parsing an SQL:
1. Optimizer evaluates your statement, checks it for grammar errors, grants to objects, etc.
2. Statement Transformation: Optimizer evaluates your statement for possible optimization regarding rewrite, in cases you have view or correlated subqueries.
3. Choice of optimizer goals.
4. Choice of acccess paths.
5. Choice of Join Orders.
Suggest you try a google search, it will give you a lot of material, or check the Oracle Database Performance Tuning Guide 11.2, which is free by oracle.

Strange behavior of explain plan

Hello i don't know if this is the correct category for posting my issue.
I ma facing a strange behavior of the explain plan. What i mean!
I have a query which runs very fast and it is well optimized. the explain plan shows very good results in cost and execution time.
when i am running the query for a second or a third time is appearing a different explain plan with not such a good cost and execution time.
Could you please guide me what it might be wrong???
thanks a lot

HI i found the correct category
thanks

Reg:Tkprof, awr, explain plan, autotrace analysis

hi friends.
can any one give description about below subject..........
Tkprof,
awr,
explain plan,
autotrace analysis
if possible kindly mentioned some example for each OR provide some to read.
regards,
Rajnish

They're all described in the Oracle Documentation, example:
http://www.oracle.com/pls/db112/search?remark=quick_search&word=AWR&partno=
Look in the [Performance Tuning Guide|http://download.oracle.com/docs/cd/E11882_01/server.112/e10821/toc.htm] for examples/exaplanations.
Randolf Geist sums it all up very nice here: http://oracle-randolf.blogspot.com/2009/02/basic-sql-statement-performance.html
More examples can be found on http://asktom.oracle.com
and on this forum by simply doing a search.

How to run Explain Plan for SP?

Can we run Explain Plan for SP??

EXPLAIN PLAN creates an execution plan for SQL statements. PL/SQL is not SQL.
PL/SQL procedures can contain SQL, yes. These SQLs can be copied and pasted from PL/SQL into something like TOAD and execution plan determined.
However, if the aim is to see the "execution/performance plan" for PL/SQL code, then you need to profile the PL/SQL code using the DBMS_PROFILER package. This will tell you the execution path and elapsed time to execute a line of PL/SQL.
Details can be found in the [url http://download-east.oracle.com/docs/cd/B19306_01/appdev.102/b14258/d_profil.htm#sthref5502]Oracle® Database PL/SQL Packages and Types Reference guide.

TUNNING A SQL QUERY AND UNSERSTAND EXPLAIN PLAN

I was trying my handing in tunning sql queries -
Though I have manged to reduce the cost lil ..creating some index, but have genarated a g8 interesting in tunning - Can some experts ( I know there are lots available :-) ) help me on the approch on "HOW TO TUNE A QUERY"
moreover I also would like to understand - how to debug a explain plan, - please help ...
Regards..

Hi,
Welcome to this forum...
I would suggest your to read first the official documentations :
- The concepts of an Oracle DBMS (this is important to know, because Oracle structures, processes, objects (etc) are the building blocks of your database)
- SQL reference guide
- PL/SQL reference guide
and then at a later stage the Performance and tuning guide:
You can start there:
http://download.oracle.com/docs/cd/B14117_01/nav/portal_1.htm
Once it's done maybe read the Performance and tuning guide:
http://download.oracle.com/docs/cd/B14117_01/server.101/b10752/toc.htm
(Chapter 19 explain ... how to interpret the explain plan ..)
I wish you good chance and be patient: I'm working with Oracle for more that 10 years and I'm still learning! ...
Rem: The Oracle website is full of interesting articles, and examples, just "search" your special points of interests ..

Problems with explain plan and statement

Hi community,
I have migrated a j2ee application from DB2 to Oracle.
First some facts of our application and database instance:
We are using oracle version 10.2.0.3 and driver version 10.2.0.3. It runs with charset Unicode 3.0 UTF-8.
Our application is using Tomcat as web container and jboss as application server. We are only using prepared statements. So if I talk about statements I always mean prepared statements. Also our application is setting the defaultNChar property to true because every char and varchar field has been created as an nchar and nvarchar.
We have some jsp sites that contains lists with search forms. Everytime I enter a value to the form that returns a filled resultset, the lists are performing great. But everytime I enter a value that returns an empty resultset, the lists are 100 times slower. The jsp sites are running in the tomcat environment and submitting their statements directly to the database. The connections are pooled by dbcp. So what can cause this behaviour??
To anaylze this problem I started logging all statements and filled-in search field values and combinations that are executed by the lists described above. I also developed a standalone helper tool that reads the logged statements, executes them to the database and generates an explain plan for every statement. But now there appears a strange situation. Every statement, that performs really fast within our application, is now executed by the helper tool extremely slow. So I edited some jsp pages within our application to force an explain plan from there (tomcat env). So when I'm executing the same statement I'm getting with the exactly same code two completely different explain plans.
First the statement itself:
select LINVIN.BBASE , INVINNUM , INVINNUMALT , LINVIN.LSUPPLIERNUM , LSUPPLIERNUMEXT , LINVIN.COMPANYCODE , ACCOUNT , INVINTXT , INVINSTS , INVINTYP , INVINDAT , RECEIPTDAT , POSTED , POSTINGDATE , CHECKCOSTCENTER , WORKFLOWIDEXT , INVINREFERENCE , RESPONSIBLEPERS , INVINSUM_V , INVINSUMGROSS_V , VOUCHERNUM , HASPOSITIONS , PROCESSINSTANCEID , FCURISO_V , LSUPPLIER.AADDRLINE1 from LINVIN, LSUPPLIER where LINVIN.BBASE = LSUPPLIER.BBASE and LINVIN.LSUPPLIERNUM = LSUPPLIER.LSUPPLIERNUM and LINVIN.BBASE = ? order by LINVIN.BBASE, INVINDAT DESC
Now the explain plan from our application:
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 101 | 28583 | 55 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 101 | 28583 | 55 (0)| 00:00:01 |
| 2 | TABLE ACCESS BY INDEX ROWID| LINVIN | 93709 | 12M| 25 (0)| 00:00:01 |
|* 3 | INDEX RANGE SCAN | LINV_INVDAT | 101 | | 1 (0)| 00:00:01 |
| 4 | TABLE ACCESS BY INDEX ROWID| LSUPPLIER | 1 | 148 | 1 (0)| 00:00:01 |
|* 5 | INDEX UNIQUE SCAN | PK_177597 | 1 | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
3 - access("LINVIN"."BBASE"=:1)
filter("LINVIN"."BBASE"=:1)
5 - access("LSUPPLIER"."BBASE"=:1 AND "LINVIN"."LSUPPLIERNUM"="LSUPPLIER"."LSUPPLIERNUM")
Now the one from the standalone tool:
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
| 0 | SELECT STATEMENT | | 93773 | 25M| | 12898 (1)| 00:02:35 |
| 1 | SORT ORDER BY | | 93773 | 25M| 61M| 12898 (1)| 00:02:35 |
|* 2 | HASH JOIN | | 93773 | 25M| 2592K| 7185 (1)| 00:01:27 |
| 3 | TABLE ACCESS BY INDEX ROWID| LSUPPLIER | 16540 | 2390K| | 332 (0)| 00:00:04 |
|* 4 | INDEX RANGE SCAN | LSUPPLIER_HAS_BASE_FK | 16540 | | | 11 (0)| 00:00:01 |
| 5 | TABLE ACCESS BY INDEX ROWID| LINVIN | 93709 | 12M| | 6073 (1)| 00:01:13 |
|* 6 | INDEX RANGE SCAN | LINVOICE_BMDT_FK | 93709 | | | 84 (2)| 00:00:02 |
Predicate Information (identified by operation id):
2 - access("LINVIN"."BBASE"="LSUPPLIER"."BBASE" AND "LINVIN"."LSUPPLIERNUM"="LSUPPLIER"."LSUPPLIERNUM")
4 - access("LSUPPLIER"."BBASE"=:1)
6 - access("LINVIN"."BBASE"=:1)
The size of the tables are: LINVIN - 383.692 Rows, LSUPPLIER - 115.782 Rows
As you can see the one executed from our application is much faster than the one from the helper tool. So why picks oracle a completely different explain plan for the same statement? An why is a hash join much slower than a nested loop? Because If I'm right a nested loop should only be used when the tables are pretty small..
I also tried to play with some parameters:
I set optimizer_index_caching to 100 and optimizer_index_cost_adj to 30. I also changed optimizer_mode to FIRST_ROWS_100.
I would really appreciated, if somebody can help me with this issue, because I'm really getting more and more distressed...
Thanks in advance,
Tobias
Edited by: tobiwan on Sep 3, 2008 11:49 PM
Edited by: tobiwan on Sep 3, 2008 11:50 PM
Edited by: tobiwan on Sep 4, 2008 12:01 AM
Edited by: tobiwan on Sep 4, 2008 12:02 AM
Edited by: tobiwan on Sep 4, 2008 12:04 AM
Edited by: tobiwan on Sep 4, 2008 12:06 AM
Edited by: tobiwan on Sep 4, 2008 12:06 AM
Edited by: tobiwan on Sep 4, 2008 12:07 AM

tobiwan wrote:
Hi again,
Here ist the answer:
The problem, because I got two different explain plans, was that the external tool uses the NLS sesssion parameters coming from the OS which are in my case "de/DE".
Within our application these parameters are changed to "en/US"!! So if I'm calling in my external tool the java function Locale.setDefault(new Locale("en","US")) before connecting to the database the explain plans are finally equal.That might explain why you got two different execution plan, because one plan was obviously able to avoid a SORT ORDER BY operation, whereas the second plan required to run SORT ORDER BY operation, obviously because of the different NLS_SORT settings. An index by default uses the NLS_SORT = 'binary' order whereas ORDER BY obeys the NLS_SORT setting, which probably was set to 'GERMAN' in your "external tool" case. You can check the "NLS_SESSION_PARAMETERS" view to check your current NLS_SORT setting.
For more information regarding this issue, see my blog note I've written about this some time ago:
http://oracle-randolf.blogspot.com/2008/09/getting-first-rows-of-large-sorted.html
Now let me make a guess why you observe the behaviour that it takes so long if your result set is empty:
The plan avoiding the SORT ORDER BY is able to return the first rows of the result set very quickly, but could take quite a while until all rows are processed, since it requires potentially a lot of iterations of the loop until everything has been processed. Your front end probably by default only display the first n rows of the result set and therefore works fine with this execution plan.
Now if the result set is empty, depending on your data, indexes and search criteria, Oracle has to work through all the data using the inefficient NESTED LOOP approach only to find out that no data has been found, and since your application attempts to fetch the first n records, but no records will be found, it has to wait until all data has been processed.
You can try to reproduce this by deliberately fetching all records of a query that returns data and that uses the NESTED LOOP approach... It probably takes as long as in the case when no records are found.
Note that you seem to use bind variables and 10g, therefore you might be interested that due to the "bind variable peeking" functionality you might potentially end up with "unstable" plans depending on the values "peeked" when the statement is parsed.
For more information, see this comprehensive description of the issue:
http://www.pythian.com/blogs/867/stabilize-oracle-10gs-bind-peeking-behaviour-by-cutting-histograms
Note that this changes in 11g with the introduction of the "Adaptive Cursor Sharing".
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/

Cpu time is not getting displayed in explain plan

Hi All,
I am trying to analyze one query using explain plan .like below
1) explain plan for
SELECT /*+ parallel(tsp,8) use_hash( tsp tp) */ count(1)
FROM router tp,
receiver tsp
WHERE tp.rs = tsp.rp
AND creater_date >=to_date('04032009000000','ddmmyyyyhh24miss')
and tsp.XVF is not null
and tp.XVF is not null
and tp.role_name='BR';
2)@$ORACLE_HOME/rdbms/admin/utlxpls.sql
But i am getting only following columns in result .
| Id | Operation | Name | Rows | Bytes | Cost |
No Cpu time preset .
How can i extimate CPU time ?
Pls help
Thanks

am_73798 wrote:
I am trying to analyze one query using explain plan .like below
But i am getting only following columns in result .
| Id | Operation | Name | Rows | Bytes | Cost |
No Cpu time preset .
How can i extimate CPU time ?You need to mention your database version (4-digits, e.g. 9.2.0.8).
In Oracle 9i CPU costing is disabled by default, you need to gather WORKLOAD system statistics to enable the CPU costing.
In 10g CPU costing is enabled by default and uses default NOWORKLOAD system statistics if no WORKLOAD system statistics have been gathered. It can only be disabled by setting an undocumented parameter or by changing the OPTIMIZER_FEATURES_ENABLE parameter back to 9i compatibility.
You can check the status of your system statistics by running the following query in SQL*Plus:
column sname format a20
column pname format a20
column pval2 format a20
select
sname
, pname
, pval1
, pval2
from
sys.aux_stats$;Can you show us the actual (complete) output you get from "utlxpls.sql"? Use the \ tag to preserve formatting here:
\output
\will show asoutput
Regards,
Randolf
Oracle related stuff blog:
http://oracle-randolf.blogspot.com/
SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/

Not Understanding the filter in Explain Plan - filter(NULL IS NOT NULL)

Hi All,
Request your help in understanding the below scenario. (I am not aware of teh application and table details. Just trying to help my friend)
SQL> conn
Enter user-name: [email protected]
Enter password:
Connected.
SQL> select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bi
PL/SQL Release 10.2.0.3.0 - Production
CORE    10.2.0.3.0      Production
TNS for Linux: Version 10.2.0.3.0 - Production
NLSRTL Version 10.2.0.3.0 - Production
--Checking the count in PO_LINES
SQL> select count(*) from po_lines;
COUNT(*)
         0
--PO_LINES is a synonym
SQL> select object_type,owner from dba_objects where object_name = 'PO_LINES';
OBJECT_TYPE         OWNER
SYNONYM             APPS
--The synonym is pointing to PO.PO_LINES_ALL
SQL> select * from user_synonyms where synonym_name = 'PO_LINES';
SYNONYM_NAME                   TABLE_OWNER                    TABLE_NAME                     DB_LINK
PO_LINES                       PO                             PO_LINES_ALL
--But when counting PO.PO_LINES_ALL I am getting different result
SQL> select count(*) c from po.po_lines_all;
         C
      8828
--Explain plan of teh original query is
SQL> explain plan for
2 select
3 * from po_lines;
Explained.
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
| Id | Operation          | Name         | Rows | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT   |              |     1 |   252 |     0   (0)|
|* 1 | FILTER            |              |       |       |            |
|   2 |   TABLE ACCESS FULL| PO_LINES_ALL | 8796 | 2164K|   106   (4)|
Predicate Information (identified by operation id):
   1 - filter(NULL IS NOT NULL)
--Now the object PO.PO_LINES_ALL is TABLE, not an mview.
SQL> select object_type,owner from dba_objects where object_name = 'PO_LINES_ALL';
OBJECT_TYPE         OWNER
TABLE               POSeek your help in understanding what is happening here.
Thanks in Advance,
jeneesh

Next time, prefix with APPS. when you show us the explain plan:
SQL> explain plan for
2 select
3 * from apps.po_lines; -- added the prefix of owner.Just like you prefixed with PO. when you showed us the query on PO_LINES_ALL. It ensures that you are using the synonym which you showed us.
Btw. PO_LINES_ALL, could still be a VIEW given your overview of the situation.
Anyway a filter "NULL IS NOT NULL" is indicative that the optimizer performed something called semantic query optimization (SQO).
SQO is the process of deducing new predicates based upon a) existing predicates in your query (which there is none), b) added predicates to your query (eg. by a VPD policy function), and c) declared constraints on the tables invovled in your query.
A typical example of when a "NOT is NOT NULL" predicate will show up is when for instance in the EMP table there is a declared constraint on EMPNO like this:
check(EMPNO > 0)And your query would hold a predicate that is inconsistent with the constraint, for instance like this:
select *
from EMP
where EMPNO <= 0Oracle will deduce that EMPNO cannot be both greater than zero (constraint) as well as smaller than or equal to zero (your query predicate), and will transform the query into:
select *
from EMP
where EMPNO <= 0
and NULL is NOT NULLThus preventing accessing the EMP table all together, and immediately returning this query with no data found.
Edited by: Toon Koppelaars on Mar 15, 2010 7:17 AM

Filter(NULL IS NOT NULL) in Explain Plan ??

Hi All,
Can someone please explain what this explain plan statement means? I see a filter(NULL IS NOT NULL) as the first statement - could not figure out why it came up so from googling.
My Query Used:
EXPLAIN PLAN FOR
MERGE INTO summary_bysrccd
USING
(SELECT LAST_DAY(TRUNC(to_timestamp(os.requestdatetime, 'yyyymmddhh24:mi:ss.ff4'))) AS SUMMARY_DATE,
os.acctnum,
ol.sourcecode AS sourcecode,
ol.sourcename AS sourcename,
count(1) cnt_articleview
FROM article_views os , master_sourcecode ol
where os.sourcecode = ol.sourcecode
AND os.acctnum IS NOT NULL
AND ol.sourcecode IS NOT NULL
AND os.requestdatetime IS NOT NULL
AND UPPER(os.success_ind) = 'S'
     AND (
          ('INCR' = 'FULL'
          AND (get_date_timestamp(os.requestdatetime) BETWEEN TO_DATE('23-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('27-AUG-2011 23:59:59','DD-MON-YYYY HH24:MI:SS')
          AND   os.entry_CreatedDate BETWEEN TO_DATE('22-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('28-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS')
          OR ('INCR' = 'FULL'
          AND os.entry_createddate BETWEEN TO_DATE('23-AUG-2011 00:00:00','DD-MON-YYYY HH24:MI:SS') AND TO_DATE('27-AUG-2011 23:59:59','DD-MON-YYYY HH24:MI:SS') )
group by LAST_DAY(TRUNC(to_timestamp(os.requestdatetime, 'yyyymmddhh24:mi:ss.ff4'))),
os.acctnum,ol.sourcecode,ol.sourcename) mrg_query
ON (ods_av_summary_bysrccd.acctnum = mrg_query.acctnum AND
ods_av_summary_bysrccd.summary_date=mrg_query.summary_date AND
ods_av_summary_bysrccd.sourcecode=mrg_query.sourcecode)
WHEN NOT MATCHED THEN
INSERT (SUMMARY_date,ACCTNUM,SOURCECODE,SOURCENAME,CNT_ARTICLEVIEW,ENTRY_LASTUPDATEDDATE)
VALUES(mrg_query.summary_date,mrg_query.acctnum,mrg_query.sourcecode,mrg_query.sourcename,
mrg_query.cnt_articleview,sysdate)
WHEN MATCHED THEN
UPDATE SET ods_av_summary_bysrccd.cnt_articleview=
CASE WHEN NVL('INCR','INCR') = 'FULL' THEN mrg_query.cnt_articleview
ELSE ods_av_summary_bysrccd.cnt_articleview+mrg_query.cnt_articleview
END,
ods_av_summary_bysrccd.entry_lastupdateddate=sysdate;My Explain Plan:
SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
Plan hash value: 268591246
| Id | Operation                                 | Name                      | Rows | Bytes |TempSpc| Cost (%CPU)| Time     | Pstart| Pstop |
|   0 | MERGE STATEMENT                           |                           |     1 |   456 |       |     3   (0)| 00:00:01 |       |       |
|   1 | MERGE                                    | ODS_AV_SUMMARY_BYSRCCD    |       |       |       |            |          |       |       |
|   2 |   VIEW                                    |                           |       |       |       |            |          |       |       |
|   3 |    NESTED LOOPS OUTER                     |                           |     1 |   417 |       |     3   (0)| 00:00:01 |       |       |
|   4 |     VIEW                                  |                           |     1 |   360 |       |     5 (100)| 00:00:01 |       |       |
|   5 |      SORT GROUP BY                        |                           |     1 |    73 |   595M|            |          |       |       |
PLAN_TABLE_OUTPUT
|* 6 |       FILTER                              |                           |       |       |       |            |          |       |       |
|* 7 |        HASH JOIN                          |                           | 6975K|   485M| 3944K| 17594   (1)| 00:03:32 |       |       |
|   8 |         TABLE ACCESS FULL                 | ODS_MASTER_SOURCECODE     | 84021 | 2953K|       |   273   (1)| 00:00:04 |       |       |
|* 9 |         TABLE ACCESS BY GLOBAL INDEX ROWID| ODS_ARTICLE_VIEWS         | 7007K|   247M|       |   826   (0)| 00:00:10 |    33 |    33 |
|* 10 |          INDEX FULL SCAN                  | IDX_AV_ACCTNUM            |    25M|       |       |    26   (0)| 00:00:01 |       |       |
| 11 |     TABLE ACCESS BY GLOBAL INDEX ROWID    | ODS_AV_SUMMARY_BYSRCCD    |     1 |    57 |       |     3   (0)| 00:00:01 | ROWID | ROWID |
|* 12 |      INDEX UNIQUE SCAN                    | ODS_AV_SUMMARY_BYSRCCD_PK |     1 |       |       |     2   (0)| 00:00:01 |       |       |
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
   6 - filter(NULL IS NOT NULL)
   7 - access("OS"."SOURCECODE"="OL"."SOURCECODE")
   9 - filter("OS"."REQUESTDATETIME" IS NOT NULL AND "OS"."ENTRY_CREATEDDATE">=TO_DATE(' 2011-08-23 00:00:00', 'syyyy-mm-dd
              hh24:mi:ss') AND "OS"."ENTRY_CREATEDDATE"<=TO_DATE(' 2011-08-27 23:59:59', 'syyyy-mm-dd hh24:mi:ss') AND UPPER("OS"."SUCCESS_IND")='S')
10 - filter("OS"."ACCTNUM" IS NOT NULL)
12 - access("ODS_AV_SUMMARY_BYSRCCD"."SUMMARY_DATE"(+)=INTERNAL_FUNCTION("MRG_QUERY"."SUMMARY_DATE") AND
              "ODS_AV_SUMMARY_BYSRCCD"."ACCTNUM"(+)="MRG_QUERY"."ACCTNUM" AND "ODS_AV_SUMMARY_BYSRCCD"."SOURCECODE"(+)="MRG_QUERY"."SOURCECODE")
Note
PLAN_TABLE_OUTPUT
   - dynamic sampling used for this statement

Hi Toon,
Thanks for the quick resolution. I went back and verified the table's colunm details and it has a NOT NULL constraint.
Regards,
Chaitanya
P.S: Is it ok if I ask you for some help regarding a production issue I have been encountering since 15 days but haev no clear resolution yet about what/why is the reason (the said issue is neither uniform nor regular - its affecting some modules and happening on some days - i shall give the full details if you are willing to have a look) - i shall start a new post or email you directly - yur convenience.

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