>> ERROR: canceling autovacuum task
>> CONTEXT: automatic vacuum of table "metadb.test.transactions"
>
> Are these happening regularly? They indicate that something is
> happening on the table that collides with what autovacuum needs to do,
> and autovacuum defers its task. For this to happen you need to be doing
> ALTER TABLE or similar however; normal UPDATE/INSERT/DELETE should not
> cause autovacuum to cancel itself.
>
I am not using an ALTER table command but I am doing periodic ANALYZEs
to evaluate the table size. Could this be causing the problem? I notice
that stopping the ANALYZE calls appears to eliminate the canceled
autovacuum.
I am trying to reproduce the case here, but could not. Can you post the table
schema and the operations you are carrying out ? Is it just INSERT new rows
and DELETE old rows or are there any UPDATEs too ? Are there any long
running transactions open ?
It'll take a few minutes but I'll try and get the information to you. A
summary is:
Process 1:
- writing 50 rows/second, 1 row/transaction.
- every so often delete 100 rows
Process 2:
- running ANALYZE VERBOSE and pg_total_relation_size every second
The result is that autovacuum appears to be canceled.
I was incorrect about autovacuum not recovering. Once I stop the
ANALYZEs it appears to stabilise and recover some of the space after a
little while. At that point a VACUUM FULL does help, and recovers quite
a bit of space. I'll run through this again here and provide you with
logs and VACUUM printouts.
What concerns me is that once the size has grown, even a VACUUM FULL
doesn't recover the space. Regular external VACUUMs keep the table at
around 10MB but if I use autovacuum and it grows to 40MB, a VACUUM FULL
will only get it down to 35MB. Is it possible that a canceled autovacuum
could result in permanently lost space?
AFAIK it should not. Can you also post VACUUM FULL VERBOSE output ?
Thanks for your help,
Stuart
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