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

On Fri, Feb 7, 2014 at 10:47 AM, Claudio Freire <klaussfreire(at)gmail(dot)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;

Cheers,

Jeff