Re: CLUSTER and synchronized scans and pg_dump et al

On Jan 28, 2008, at 8:36 AM, Tom Lane wrote:

> Andrew Dunstan <andrew@dunslane.net> writes:
>> Kevin Grittner wrote:
>>> It would seem reasonable to me for pg_dump to use ORDER BY to select
>>> data from clustered tables.
>
>> What will be the performance hit from doing that?
>
> That worries me too.  Also, in general pg_dump's charter is to  
> reproduce
> the state of the database as best it can, not to "improve" it.

One common use of cluster around here is to act as a faster version
of vacuum full when there's a lot of dead rows in a table. There's no
intent to keep the table clustered on that index, and the cluster flag
isn't removed with alter table (why bother, the only thing it affects is
the cluster command).

I'm guessing that's not unusual, and it'd lead to sorting tables as part
of pg_dump.

Cheers,  Steve