RE: stale partition statistics

From: Noveljic Nenad <nenad.noveljic_at_vontobel.com>
Date: Mon, 8 Mar 2021 19:26:20 +0000
Message-ID: <0390fec168124d41967d67dbaaa1ea60_at_vontobel.com>

Hi Mikhail,

Yes, non-zero flags definitely trigger gathering of stale statistics regardless of the number of modifications. For flags = 1 that’s a correct behavior, since it’s a truncate. For flags=8 we still don’t know. I’m going to chase the application people tomorrow to rerun the load jobs on the restored database. I hope I’ll catch the culprit in the trace.

Best regards,

Nenad

From: Mikhail Velikikh <mvelikikh_at_gmail.com> Sent: Montag, 8. März 2021 20:13
To: Noveljic Nenad <nenad.noveljic_at_vontobel.com> Cc: Jonathan Lewis <jlewisoracle_at_gmail.com>; ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>; nigel.bayliss_at_oracle.com; neil_chandler_at_hotmail.com Subject: Re: stale partition statistics

Hi Nenad,

I got the same flags after one database upgrade from 12.2 to 19.7. Basically, there was a list partitioned table, and the gather stats job started collecting statistics on the table's indexes everyday following the 19.7 upgrade (I believe on the global ones). While I was investigating the issue, I found that some of data dictionary views were looking at that MON_MODS_V.FLAGS to determine the staleness - that is why the statistics were regathered every day. The exact meaning of that flags value is somewhere in DBMS_STATS or the packages calling from it - at least that is where I found it then.

I checked my notes, and I tried several different things to get stats back to normal, such as: exec dbms_stats.delete_table_stats('owner', 'table_name', stat_category=> 'OBJECT_STATS,SYNOPSES') exec dbms_stats.gather_table_stats('owner', 'table_name')

The statistics preferences were as follows: SQL> SELECT
  2 owner, table_name,

  3  DBMS_STATS.get_prefs(ownname=>USER,tabname=>table_name,pname=>'INCREMENTAL') incremental,
  4  DBMS_STATS.get_prefs(ownname=>USER,tabname=>table_name,pname=>'GRANULARITY') granularity,
  5  DBMS_STATS.get_prefs(ownname=>USER,tabname=>table_name,pname=>'STALE_PERCENT') stale_percent,
  6  DBMS_STATS.get_prefs(ownname=>USER,tabname=>table_name,pname=>'ESTIMATE_PERCENT') estimate_percent,
  7  DBMS_STATS.get_prefs(ownname=>USER,tabname=>table_name,pname=>'CASCADE') cascade,
  8  DBMS_STATS.get_prefs(pname=>'METHOD_OPT') method_opt

  9 FROM dba_tables
 10 WHERE table_name ='table_name'
 11 and owner='owner'
 12 ORDER BY owner, table_name;

OWNER      TABLE_NAME           INCREMENTAL          GRANULARITY          STALE_PERCENT        ESTIMATE_PERCENT               CASCADE                   METHOD_OPT
---------- -------------------- -------------------- -------------------- -------------------- ------------------------------ ------------------------- -------------------------
owner         table_name TRUE                 AUTO                 10                   DBMS_STATS.AUTO_SAMPLE_SIZE    DBMS_STATS.AUTO_CASCADE   FOR ALL COLUMNS SIZE 1

There was also INCREMENTAL_STALENESS=USE_STALE_PERCENT set.

The way I checked the flags is using the query like this: select * from sys.optstat_snapshot$ where obj#=185925 order by timestamp;

      OBJ# INSERTS UPDATES DELETES FLAGS TIMESTAMP

---------- ---------- ---------- ---------- ---------- ---------------------------------------------------------------------------
    185925     165103     557906          0          0 11-MAY-20 10.18.43.791891 PM -04:00
    185925     603978     558015          0          0 11-MAY-20 11.18.47.734575 PM -04:00
    185925     673059     558524          0          0 12-MAY-20 01.03.54.386869 AM -04:00
    185925    1294183     605041          0          0 12-MAY-20 02.03.58.300521 AM -04:00
    185925    1358957     692646          0         40 12-MAY-20 02.35.52.733528 AM -04:00
    185925          0     242425          0          0 12-MAY-20 03.34.04.838415 AM -04:00
    185925          0     242425          0         40 12-MAY-20 03.59.42.940827 AM -04:00
    185925          0          1          0         40 12-MAY-20 04.08.15.887380 AM -04:00
    185925          0          0          0         40 12-MAY-20 04.15.45.580398 AM -04:00
    185925          0        638          0         40 12-MAY-20 04.25.43.490814 AM -04:00
    185925          0        278          0         40 12-MAY-20 04.35.57.022339 AM -04:00
    185925          0       8581          0         40 12-MAY-20 04.45.40.478107 AM -04:00
    185925          0      85532          0         40 12-MAY-20 04.55.37.699201 AM -04:00
    185925      89737          0          0          0 17-MAY-20 10.32.00.757830 PM -04:00
    185925     175288      13533          0          0 17-MAY-20 11.32.05.038541 PM -04:00
    185925     175288      13533          0          0 18-MAY-20 12.32.08.422136 AM -04:00
    185925     175288      13533          0          0 18-MAY-20 01.32.12.059589 AM -04:00
    185925     175288      13533          0         40 18-MAY-20 02.32.01.836936 AM -04:00
    185925          0          0          0         40 18-MAY-20 03.33.57.325283 AM -04:00
    185925      12005          0          0          0 18-MAY-20 08.44.27.382584 AM -04:00
    185925      12005        941          0          0 18-MAY-20 09.44.29.421376 AM -04:00
    185925      12005       4159          0          0 18-MAY-20 10.44.32.184351 AM -04:00
    185925      12005       5365          0          0 18-MAY-20 11.44.33.433158 AM -04:00
    185925      12005       5365          0          0 18-MAY-20 12.44.34.162253 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 01.44.35.163062 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 02.44.36.352044 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 03.44.37.308166 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 04.44.38.309023 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 05.44.39.285316 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 06.44.40.241425 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 07.44.41.296872 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 08.44.42.524968 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 09.44.43.561849 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 10.44.44.638588 PM -04:00
    185925      12005       5365          0          0 18-MAY-20 11.44.48.566198 PM -04:00
    185925      12005       5365          0          0 19-MAY-20 12.44.49.587112 AM -04:00
    185925      12005       5365          0          0 19-MAY-20 01.44.50.610348 AM -04:00
    185925      12005       5365          0          8 19-MAY-20 03.29.52.937021 AM -04:00
    185925      12005       5365          0          8 19-MAY-20 04.29.54.274754 AM -04:00
..skip...
    185925      39055   55056337          0          8 22-MAY-20 01.52.22.127686 PM -04:00
    185925      39055   55056337          0          8 22-MAY-20 02.52.23.180742 PM -04:00
    185925      39055   55056337          0          8 22-MAY-20 03.52.24.267023 PM -04:00
    185925      39055   55056337          0         40 22-MAY-20 04.24.02.507669 PM -04:00
    185925          0          0          0          8 23-MAY-20 04.37.38.529168 AM -04:00

I think I hit that issue in multiple environments. The flags was set to 8 following the upgrade and then I could not get rid of it. Raised an SR with Oracle, but it went nowhere. The flags switching from 8 to 40 and backwards might be due to the statistics gathering - cannot recall.

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Received on Mon Mar 08 2021 - 20:26:20 CET