Re: autovacuum not freeing up unused space on 8.3.0

>>  >> 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