Re: Variable execution time of sql with same plan

Hi Pap,

You didn't include the captured bind variables (these can be trusted in live report monitors) but there's enough to go off with what you included.

To start, your faster execution is still 3 minutes and is doing 11M buffer gets - mostly reading 108M rows from SFE from your SFE_IX1 index to end up with 15000 rows. Keep that in mind.

Your second execution, the additional time is mostly IO and we can see that this IO is mostly on the SFE & SFE_IX1 lines (going from 170K physical IOs to 864K IOs. Judging by the buffer gets, my first guess would be that of all the buffers that needed reading (we already know there's millions) a lot more were not found in cache in this execution.

The third execution is a bit more obvious, the index range scan of SFE_IX1 identifies 4G rows which all need looking up in SFE (to end up with 14998).

Based on this, the starting suggestion would be to improve how you are accessing SFE. We can see the additional predicates that get applied on line 8 that aren't solved by your index. It looks like "sfhid" and "oid" could be good candidates for adding to the index. If that's not enough then the ptcode column could be added.

Thanks,
Andrew

On Fri, 26 Nov 2021 at 12:36, Pap <oracle.developer35_at_gmail.com> wrote:

> Hello All, It's version 12.1.0.2.0 of oracle database with
> optimizer_feature_enable set as 11.2.0.4. We have the below query which
> sometimes runs in ~3-4minutes and sometimes goes for ~10minutes or even
> ~1hrs also. As its version 12.1 so was able to capture the sql monitor for
> a few of the good and bad runs for comparison. So I wanted to understand
> what is the reason behind the same and if we can make it better?
>
> From the sql monitor it seems , it's the plan_line_id 8 and 9 i.e.
> fetching rows from table SFE using index SFE_IX1 is making the difference.
> But I want to understand , how come the difference is so much with the same
> plan hash value and even the EXECS column in the sql monitor shows the same
> amount of iteration in those index access steps?
>
> SELECT *
> FROM (SELECT /*+ ordered index(SFE SFE_IX1) index(SBD SBD_IX1) */
> ....,
> ROW_NUMBER ()
> OVER (PARTITION BY SBD.BDID
> ORDER BY SFE.FID DESC) rn
> FROM SBD , SFE ,STD
> WHERE SFE.fhid = SBD.sfhid AND SFE.eid = STD.did AND
> SFE.eid = SBD.did AND SFE.oid = SBD.sid AND SFE.ptcode IN ('XX',
> 'YY', 'ZZ')
> AND SFE.ETYP = 'ZZZZ' AND NVL (SFE.SCID, '0') = NVL
> (SBD.SCID, 0) AND SBD.P_DT = SFE.P_DT AND SBD.HD_ID = :b1 AND SBD.STAT =
> :b2)
> WHERE rn < 2;
>
> Table SBD having total ~1.7million rows and table STD having ~4.2million
> rows.
>
> SFE is the biggest one having ~1.7billion rows and partitioned. But all
> the indexes are global here. and the partition key is not used in the
> filter/join criteria. We have four indexes on the columns of the table that
> are used as join/filter predicate in this query.
>
> COLUMN_NAME NUM_DISTINCT DENSITY NUM_NULLS HISTOGRAM
> EIS 367397 2.72185E-06 0 NONE
> ETYP 2 0.5 0 NONE
> OID 219100 4.56413E-06 0 NONE
> FHID 558916 1.78918E-06 0 NONE
> PTCODE 419 0.002386635 0 NONE
> SCID 1742 0.000574053 1693771500 NONE
> P_DT 6546 0.0001527 0 NONE
>
> Index SFE_IX4 - On column ptcode.
> Index SFE_IX2 - On column fhid.
> Index SFE_X1 - On column etyp , eid.
> Index SFE_TMP - On column p_dt.
>
> INDEX_NAME BLEVEL LEAF_BLOCKS CLUSTERING_FACTOR NUM_ROWS distinct_keys
> SFE_IX4 4 12553800 456127300 1670902700 419
> SFE_IX2 4 13526400 79324200 1771657400 558916
> SFE_X1 4 9883200 168223500 1730409900 367397
> SFE_TMP 4 15856000 74249900 1737505200 6546
>
> Below are the three different sql monitors captured with a big difference
> in run time.
>
> Global Information
> ------------------------------
> Status : DONE (ALL ROWS)
> Instance ID : 1
> SQL Execution ID : 16777286
> Execution Started : 11/10/2021 01:30:27
> First Refresh Time : 11/10/2021 01:30:31
> Last Refresh Time : 11/10/2021 01:33:11
> Duration : 164s
> Program : JDBC Thin Client
> Fetch Calls : 1001
>
> Global Stats
>
> =========================================================================================
> | Elapsed | Cpu | IO | Concurrency | Cluster | Fetch | Buffer |
> Read | Read |
> | Time(s) | Time(s) | Waits(s) | Waits(s) | Waits(s) | Calls | Gets |
> Reqs | Bytes |
>
> =========================================================================================
> | 175 | 94 | 81 | 0.00 | 0.73 | 1001 | 11M |
> 170K | 1GB |
>
> =========================================================================================
>
>
> =============================================================================================================================================================================================
> | Id | Operation | Name
> | Rows | Cost | Time | Start | Execs | Rows | Read | Read
> | Mem | Activity | Activity Detail |
> | | |
> | (Estim) | | Active(s) | Active | | (Actual) | Reqs | Bytes
> | (Max) | (%) | (# samples) |
>
> =============================================================================================================================================================================================
> | 0 | SELECT STATEMENT |
> | | | 2 | +163 | 1 | 10000 | |
> | | | |
> | 1 | VIEW |
> | 1 | 1385 | 2 | +163 | 1 | 10000 | |
> | | | |
> | 2 | WINDOW SORT PUSHED RANK |
> | 1 | 1385 | 161 | +4 | 1 | 15000 | |
> | 5M | | |
> | 3 | NESTED LOOPS |
> | | | 160 | +4 | 1 | 15000 | |
> | | | |
> | 4 | NESTED LOOPS |
> | 1 | 1384 | 160 | +4 | 1 | 15000 | |
> | | | |
> | 5 | NESTED LOOPS |
> | 1 | 1382 | 160 | +4 | 1 | 15000 | |
> | | | |
> | 6 | TABLE ACCESS BY INDEX ROWID | SBD
> | 1 | 699 | 160 | +4 | 1 | 10000 | |
> | | | |
> | 7 | INDEX RANGE SCAN | SBD_IX1
> | 9476 | 79 | 160 | +4 | 1 | 10000 | |
> | | | |
> | 8 | TABLE ACCESS BY GLOBAL INDEX ROWID | SFE
> | 1 | 683 | 163 | +1 | 10000 | 15000 | 152K | 1GB
> | | | |
> | 9 | INDEX RANGE SCAN | SFE_IX1
> | 4688 | 220 | 160 | +4 | 10000 | 108M | 18160 | 142MB
> | | | |
> | 10 | INDEX UNIQUE SCAN | STD_PK
> | 1 | 1 | 161 | +4 | 15034 | 15000 | 3 |
> 24576 | | | |
> | 11 | TABLE ACCESS BY INDEX ROWID | STD
> | 1 | 2 | 160 | +4 | 15160 | 15000 | |
> | | | |
>
> =============================================================================================================================================================================================
>
>
> Global Information
> ------------------------------
> Status : DONE (ALL ROWS)
> Instance ID : 1
> SQL Execution ID : 16777285
> Execution Started : 11/10/2021 01:30:27
> First Refresh Time : 11/10/2021 01:30:31
> Last Refresh Time : 11/10/2021 01:38:48
> Duration : 501s
> Program : JDBC Thin Client
> Fetch Calls : 1001
>
> Global Stats
> ===========================================================================
> | Elapsed | Cpu | IO | Cluster | Fetch | Buffer | Read | Read |
> | Time(s) | Time(s) | Waits(s) | Waits(s) | Calls | Gets | Reqs | Bytes |
> ===========================================================================
> | 561 | 156 | 401 | 3.94 | 1001 | 9M | 864K | 7GB |
> ===========================================================================
>
>
> ============================================================================================================================================================================================
> | Id | Operation | Name
> | Rows | Cost | Time | Start | Execs | Rows | Read | Read
> | Mem | Activity | Activity Detail |
> | | |
> | (Estim) | | Active(s) | Active | | (Actual) | Reqs | Bytes
> | (Max) | (%) | (# samples) |
>
> ============================================================================================================================================================================================
> | 0 | SELECT STATEMENT |
> | | | 1 | +501 | 1 | 10000 | |
> | | | |
> | 1 | VIEW |
> | 1 | 1385 | 1 | +501 | 1 | 10000 | |
> | | | |
> | 2 | WINDOW SORT PUSHED RANK |
> | 1 | 1385 | 498 | +4 | 1 | 15000 | |
> | 5M | | |
> | 3 | NESTED LOOPS |
> | | | 498 | +4 | 1 | 15000 | |
> | | | |
> | 4 | NESTED LOOPS |
> | 1 | 1384 | 498 | +4 | 1 | 15000 | |
> | | | |
> | 5 | NESTED LOOPS |
> | 1 | 1382 | 498 | +4 | 1 | 15000 | |
> | | | |
> | 6 | TABLE ACCESS BY INDEX ROWID | SBD
> | 1 | 699 | 498 | +4 | 1 | 10000 | 5 | 40960
> | | | |
> | 7 | INDEX RANGE SCAN | SBD_IX1
> | 9476 | 79 | 498 | +4 | 1 | 10000 | |
> | | | |
> | 8 | TABLE ACCESS BY GLOBAL INDEX ROWID | SFE
> | 1 | 683 | 498 | +4 | 10000 | 15000 | 696K | 5GB
> | | | |
> | 9 | INDEX RANGE SCAN | SFE_IX1
> | 4688 | 220 | 501 | +1 | 10000 | 97M | 168K | 1GB
> | | | |
> | 10 | INDEX UNIQUE SCAN | STD_PK
> | 1 | 1 | 498 | +4 | 15045 | 15000 | 5 | 40960
> | | | |
> | 11 | TABLE ACCESS BY INDEX ROWID | STD
> | 1 | 2 | 498 | +4 | 15994 | 15000 | 2 | 16384
> | | | |
> ============================================================================================================================================================================================
>
>
> Global Information
> ------------------------------
> Status : DONE (ALL ROWS)
> Instance ID : 1
> SQL Execution ID : 16780848
> Execution Started : 09/14/2021 12:17:54
> First Refresh Time : 09/14/2021 12:17:58
> Last Refresh Time : 09/14/2021 13:22:10
> Duration : 3856s
> Program : JDBC Thin Client
> Fetch Calls : 1001
>
> Global Stats
>
> =====================================================================================================
> | Elapsed | Cpu | IO | Concurrency | Cluster | Other | Fetch
> | Buffer | Read | Read |
> | Time(s) | Time(s) | Waits(s) | Waits(s) | Waits(s) | Waits(s) | Calls
> | Gets | Reqs | Bytes |
>
> =====================================================================================================
> | 3855 | 3822 | 26 | 0.02 | 2.31 | 5.45 | 1001
> | 609M | 42879 | 335MB |
>
> =====================================================================================================
>
>
> =============================================================================================================================================================================================
> | Id | Operation | Name
> | Rows | Cost | Time | Start | Execs | Rows | Read | Read
> | Mem | Activity | Activity Detail |
> | | |
> | (Estim) | | Active(s) | Active | | (Actual) | Reqs | Bytes
> | (Max) | (%) | (# samples) |
>
> =============================================================================================================================================================================================
> | 0 | SELECT STATEMENT |
> | | | 2 | +3855 | 1 | 10000 | |
> | | | |
> | 1 | VIEW |
> | 1 | 1374 | 2 | +3855 | 1 | 10000 | |
> | | | |
> | 2 | WINDOW SORT PUSHED RANK |
> | 1 | 1374 | 3853 | +4 | 1 | 14998 | |
> | 5M | | |
> | 3 | NESTED LOOPS |
> | | | 3852 | +4 | 1 | 14998 | |
> | | | |
> | 4 | NESTED LOOPS |
> | 1 | 1373 | 3852 | +4 | 1 | 14998 | |
> | | | |
> | 5 | NESTED LOOPS |
> | 1 | 1371 | 3852 | +4 | 1 | 14998 | |
> | | | |
> | 6 | TABLE ACCESS BY INDEX ROWID | SBD
> | 1 | 677 | 3852 | +4 | 1 | 10000 | 304 | 2MB
> | | | |
> | 7 | INDEX RANGE SCAN | SBD_IX1
> | 9362 | 78 | 3852 | +4 | 1 | 10000 | 57 | 456KB
> | | | |
> | 8 | TABLE ACCESS BY GLOBAL INDEX ROWID | SFE
> | 1 | 694 | 3854 | +2 | 10000 | 14998 | 39830 | 311MB
> | | | |
> | 9 | INDEX RANGE SCAN | SFE_IX1
> | 4180 | 230 | 3851 | +4 | 10000 | 4G | 2688 | 21MB
> | | | |
> | 10 | INDEX UNIQUE SCAN | STD_PK
> | 1 | 1 | 3853 | +4 | 14998 | 14998 | |
> | | | |
> | 11 | TABLE ACCESS BY INDEX ROWID | STD
> | 1 | 2 | 3852 | +4 | 14998 | 14998 | |
> | | | |
>
> =============================================================================================================================================================================================
>
> Predicate Information (identified by operation id):
> ---------------------------------------------------
> 1 - filter("RN"<2)
> 2 - filter(ROW_NUMBER() OVER ( PARTITION BY "SBD"."BDID" ORDER BY
> INTERNAL_FUNCTION("SFE"."FID") DESC )<2)
> 6 - filter("SBD"."STAT"=:B2)
> 7 - access("HD_ID"=:B1)
> 8 - filter(("SFE"."ptcode"='ZZ' OR "SFE"."ptcode"='XX' OR
> "SFE"."ptcode"='YY') AND "SFE"."fhid"="SBD"."sfhid" AND
> "SFE"."oid"="SBD"."sid" AND
> NVL("SFE"."SCID",0)=NVL("SBD"."SCID",0) AND
> "SBD"."P_DT"="SFE"."P_DT")
> 9 - access("SFE"."ETYP"='ZZZZ' AND "SFE"."eid"="SBD"."did")
> 10 - access("SFE"."eid"="STD"."did")
>
>
>

--
http://www.freelists.org/webpage/oracle-l