Re: pg_autovacuum not having enough suction ?

It looks like the reltuples-values are screwed up. Even though rows are
constantly being removed from the table the reltuples keep going up. If I
understand correctly that also makes the Vacuum threshold go up and we end
up in a vicious circle. Right after pg_autovacuum performed a vacuum analyze
on the table it actually had 31000 records, but reltuples reports over 100k.
I'm not sure if this means anything But i thought i would pass it along.

PG version 8.0.0, 31MB tarred DB.

[2005-03-25 09:16:14 EST] INFO: dbname: testing
[2005-03-25 09:16:14 EST] INFO: oid: 9383816
[2005-03-25 09:16:14 EST] INFO: username: (null)
[2005-03-25 09:16:14 EST] INFO: password: (null)
[2005-03-25 09:16:14 EST] INFO: conn is null, (not connected)
[2005-03-25 09:16:14 EST] INFO: default_analyze_threshold: 1000
[2005-03-25 09:16:14 EST] INFO: default_vacuum_threshold: 500

[2005-03-25 09:05:12 EST] INFO: table name: secom."public"."file_92"
[2005-03-25 09:05:12 EST] INFO: relid: 9384219; relisshared: 0
[2005-03-25 09:05:12 EST] INFO: reltuples: 49185.000000; relpages:
8423
[2005-03-25 09:05:12 EST] INFO: curr_analyze_count: 919274;
curr_vacuum_count: 658176
[2005-03-25 09:05:12 EST] INFO: last_analyze_count: 899272;
last_vacuum_count: 560541
[2005-03-25 09:05:12 EST] INFO: analyze_threshold: 49685;
vacuum_threshold: 100674

[2005-03-25 09:10:12 EST] DEBUG: Performing: VACUUM ANALYZE
"public"."file_92"
[2005-03-25 09:10:33 EST] INFO: table name: secom."public"."file_92"
[2005-03-25 09:10:33 EST] INFO: relid: 9384219; relisshared: 0
[2005-03-25 09:10:33 EST] INFO: reltuples: 113082.000000; relpages:
6624
[2005-03-25 09:10:33 EST] INFO: curr_analyze_count: 923820;
curr_vacuum_count: 662699
[2005-03-25 09:10:33 EST] INFO: last_analyze_count: 923820;
last_vacuum_count: 662699
[2005-03-25 09:10:33 EST] INFO: analyze_threshold: 113582;
vacuum_threshold: 227164

[2005-03-25 09:16:14 EST] INFO: table name: secom."public"."file_92"
[2005-03-25 09:16:14 EST] INFO: relid: 9384219; relisshared: 0
[2005-03-25 09:16:14 EST] INFO: reltuples: 113082.000000; relpages:
6624 <-- Actually has 31k rows
[2005-03-25 09:16:14 EST] INFO: curr_analyze_count: 923820;
curr_vacuum_count: 662699
[2005-03-25 09:16:14 EST] INFO: last_analyze_count: 923820;
last_vacuum_count: 662699
[2005-03-25 09:16:14 EST] INFO: analyze_threshold: 113582;
vacuum_threshold: 227164

DETAIL: Allocated FSM size: 1000 relations + 2000000 pages = 11784 kB
shared memory.

----- Original Message -----
From: "Matthew T. O'Connor" <matthew(at)zeut(dot)net>
To: "Otto Blomqvist" <o(dot)blomqvist(at)secomintl(dot)com>;
<pgsql-performance(at)postgresql(dot)org>
Sent: Thursday, March 24, 2005 3:58 PM
Subject: Re: [PERFORM] pg_autovacuum not having enough suction ?

> I would rather keep this on list since other people can chime in.
>
> Otto Blomqvist wrote:
>
> >It does not seem to be a Stats collector problem.
> >
> > oid | relname | relnamespace | relpages | relisshared | reltuples |
> >schemaname | n_tup_ins | n_tup_upd | n_tup_del
>
>---------+---------+--------------+----------+-------------+-----------+---
-
> >--------+-----------+-----------+-----------
> > 9384219 | file_92 | 2200 | 8423 | f | 49837 |
> >public | 158176 | 318527 | 158176
> >(1 row)
> >
> >I insert 50000 records
> >
> >secom=# select createfile_92records(1, 50000); <--- this is a pg
script
> >that inserts records 1 threw 50000.
> > createfile_92records
> >----------------------
> > 0
> >
> >
> > oid | relname | relnamespace | relpages | relisshared | reltuples |
> >schemaname | n_tup_ins | n_tup_upd | n_tup_del
>
>---------+---------+--------------+----------+-------------+-----------+---
-
> >--------+-----------+-----------+-----------
> > 9384219 | file_92 | 2200 | 8423 | f | 49837 |
> >public | 208179 | 318932 | 158377
> >(1 row)
> >
> >reltuples does not change ? Hmm. n_tup_ins looks fine.
> >
> >
>
> That is expected, reltuples only gets updated by a vacuum or an analyze.
>
> >This table is basically a queue full of records waiting to get transfered
> >over from our 68030 system to the PG database. The records are then moved
> >into folders (using a trigger) like file_92_myy depending on what month
the
> >record was created on the 68030. During normal operations there should
not
> >be more than 10 records at a time in the table, although during the
course
> >of a day a normal system will get about 50k records. I create 50000
records
> >to simulate incoming traffic, since we don't have much traffic in the
test
> >lab.
> >
> >After a few hours we have
> >
> >secom=# select count(*) from file_92;
> > count
> >-------
> > 42072
> >
> >So we have sent over approx 8000 Records.
> >
> > oid | relname | relnamespace | relpages | relisshared | reltuples |
> >schemaname | n_tup_ins | n_tup_upd | n_tup_del
>
>---------+---------+--------------+----------+-------------+-----------+---
-
> >--------+-----------+-----------+-----------
> > 9384219 | file_92 | 2200 | 8423 | f | 49837 |
> >public | 208218 | 334521 | 166152
> >(1 row)
> >
> >
> >n_tup_upd: 318932 + (50000-42072)*2 = 334788 pretty close. (Each record
> >gets updated twice, then moved)
> >n_tup_del: 158377 + (50000-42072) = 166305 pretty close. (there are also
> >minor background traffic going on)
> >
> >
> >I could send over the full vacuum verbose capture as well as the
autovacuum
> >capture if that is of interest.
> >
>
> That might be helpful. I don't see a stats system problem here, but I
> also haven't heard of any autovac problems recently, so this might be
> something new.
>
> Thanks,
>
> Matthew O'Connor
>
>
>
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