Re: Bloated tables and why is vacuum full the only option

On Tue, Feb 11, 2014 at 8:29 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
> On Fri, Feb 7, 2014 at 10:47 AM, Claudio Freire <klaussfreire@gmail.com>
> wrote:
>>
>> Hello list.
>>
>> I know all the theory about vacuuming. I've got log tables that get
>> periodically pruned. The pruning is... quirky, though. It's not so
>> much deleting data, as summarizing many (thousands) of rows into one
>> single row. For that, a combination of deletes and updates are used.
>>
>> In essence, the tables are write-only except for the summarization
>> step for old data.
>>
>> Many tables are becoming increasingly bloated, which is somewhat
>> expected due to this usage pattern: I had expected table size to be
>> about constant, holding recent data plus archived old data (which is
>> really small compared to full recent logs), with some constant-sized
>> bloat due to daily summarization updates/deletes.
>>
>> What I'm seeing, though, is not that, but bloat proportional to table
>> size (always stuck at about 65% bloat). What's weird, is that vacuum
>> full does the trick of reducing table size and bloat back to 0%. I
>> haven't had time yet to verify whether it goes back to 65% after
>> vacuum full (that will take time, maybe a month).
>>
>> Question is... why isn't all that free space being used? The table
>> grows in size even though there's plenty (65%) of free space.
>
>
> What does this look like with the pg_bloat_report.pl you linked to?
>
> Does pg_freespace agree that that space is reusable?
>
> SELECT avail,count(*) FROM pg_freespace('pgbench_accounts') group by avail;

I don't have pg_freespacemap installed on that server.

I guess I'll take the next opportunity to install it.