RE: Used-Mem in execution plans
- From: "Ric Van Dyke" <ric.van.dyke@xxxxxxxxxx>
- To: "Tanel Poder" <tanel@xxxxxxxxxxxxxx>
- Date: Fri, 6 Jun 2014 10:32:10 -0500
Thanks Tanel.
It looks like the value in V$SQL_WORKAREA is correct (it’s in bytes) it’s the
one in V$SQL_PLAN_STATISTICS_ALL that is off. So if the value is coming from
V$SQL_WORKAREA then it’s correct, however if it’s form
V$SQL_PLAN_STATISTICS_ALL then it’s off and should be multiplied by 1024 to get
the right number of bytes. The docs say the column (LAST_TEMPSEG_SIZE) in
both tables is in bytes, but it sure looks like in V$SQL_PLAN_STATISTICS_ALL
it’s not.
So maybe the USED values come from V$SQL_PLAN_STATISTICS_ALL? Little more
digging around it looks like. Hummm…
SQL> SELECT SQL_ID, MAX_TEMPSEG_SIZE, LAST_TEMPSEG_SIZE
2 FROM V$SQL_WORKAREA
3 WHERE SQL_ID = 'g4tr51k11z5a0';
SQL_ID MAX_TEMPSEG_SIZE LAST_TEMPSEG_SIZE
------------- ---------------- -----------------
g4tr51k11z5a0 403701760 403701760
SQL>
SQL> SELECT SQL_ID, MAX_TEMPSEG_SIZE, LAST_TEMPSEG_SIZE
2 FROM V$SQL_PLAN_STATISTICS_ALL
3 WHERE SQL_ID = 'g4tr51k11z5a0';
SQL_ID MAX_TEMPSEG_SIZE LAST_TEMPSEG_SIZE
------------- ---------------- -----------------
g4tr51k11z5a0
g4tr51k11z5a0 394240 394240
g4tr51k11z5a0
SQL>
SQL> SELECT 394240*1024 FROM DUAL;
394240*1024
---------------
403701760
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Ric Van Dyke
Education Director
Oracle Ace Associate
Hotsos Ltd.
**** Hotsos Symposium
**** March 1-5 2015
Make your plans to be there now!
From: tanel@xxxxxxxxxx [mailto:tanel@xxxxxxxxxx] On Behalf Of Tanel Poder
Sent: Friday, June 06, 2014 1:01 AM
To: Ric Van Dyke
Cc: oracle-l-freelists
Subject: Re: Used-Mem in execution plans
Yep! The USED figures come from the V$SQL_WORKAREA view (the LAST_... columns).
It won't be populated until the query finishes (or is canceled). In the
brackets you have number of passes that's 0 for optimal executions (LAST_PASSES
colum I think). The Used-TMP field in DBMS_XPLAN is buggy, it's in kilobytes,
so the 385K in your output actually means 385 MB :)
--
Tanel Poder
Enkitec (The Exadata Experts)
Services <http://enkitec.com> | Training <http://blog.tanelpoder.com/seminar/>
| Troubleshooting <http://blog.tanelpoder.com/> | Exadata Book
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On Thu, Jun 5, 2014 at 11:22 AM, Ric Van Dyke <ric.van.dyke@xxxxxxxxxx> wrote:
Soft-ball here. I can’t find any documentation or blog posts that speak to
this.
When I look at an execution plan with DBMS_XPLAN.DISPLAY_CURSOR that does a
sort I see the memory used for the sort. There is now a column Used-Mem along
with the OMem and 1Mem columns. In the Used-Mem there is a number in
parentheses, I assume the number is the number of passes over/thru the memory
segment, and that a single pass would actually show a zero. Can someone
confirm or deny this?
For example:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing
options
SQL>
SQL> SELECT PLAN_TABLE_OUTPUT
2 FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR
3 ('g4tr51k11z5a0',0,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------
SQL_ID g4tr51k11z5a0, child number 0
-------------------------------------
select * from big_tab order by owner
Plan hash value: 3765827574
-----------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time |
Buffers | Reads | Writes | OMem | 1Mem | Used-Mem | Used-Tmp|
-----------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2868K|00:00:46.50 |
48224 | 97395 | 49190 | | | | |
| 1 | SORT ORDER BY | | 1 | 2868K| 2868K|00:00:46.50 |
48224 | 97395 | 49190 | 432M| 6863K| 100M (1)| 385K|
| 2 | TABLE ACCESS FULL| BIG_TAB | 1 | 2868K| 2868K|00:00:04.26 |
48215 | 48205 | 0 | | | | |
-----------------------------------------------------------------------------------------------------------------------------------------------
SQL>
Thanks
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Ric Van Dyke
Education Director
Oracle Ace Associate
Hotsos Ltd.
**** Hotsos Symposium
**** March 1-5 2015
Make your plans to be there now!
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