RE: Variable execution time of sql with same plan
Date: Fri, 26 Nov 2021 13:14:03 -0500
Message-ID: <5d4e01d7e2f1$65682a00$30387e00$_at_rsiz.com>
What Andy said, and:
Often the Oracle CBO can sort all that out for you under the covers, but if you know something about the texture of your data that will be constant you can spoon feed an easier to optimize puzzle to the CBO.
Good luck. That count grouping by ptcode and information about your partitioning could also tell us that my notion is absurd compared to the actual data. But it is worth checking. Hard coded constants in queries are a flashing neon sign to ask “what is special about these values, and can it help me write the code to get good answers faster.”
Likewise if the join of STD and SBD on did returns a large fraction of the rows with SBD filtered on its non-join predicates.
mwf
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Andy Sayer
Sent: Friday, November 26, 2021 9:03 AM
To: Pap
Cc: Oracle L
Subject: 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")
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