Re: [PERFORM] encouraging index-only scans

Bruce Momjian <bruce@momjian.us> writes:
> On Wed, Dec 12, 2012 at 05:27:39PM -0500, Andrew Dunstan wrote:
>> Actually, the table had been analysed but not vacuumed, so this
>> kinda begs the question what will happen to this value on
>> pg_upgrade? Will people's queries suddenly get slower until
>> autovacuum kicks in on the table?

> [ moved to hackers list.]

> Yes, this does seem like a problem for upgrades from 9.2 to 9.3?  We can
> have pg_dump --binary-upgrade set these, or have ANALYZE set it.   I
> would prefer the later.

ANALYZE does not set that value, and is not going to start doing so,
because it doesn't scan enough of the table to derive a trustworthy
value.

It's been clear for some time that pg_upgrade ought to do something
about transferring the "statistics" columns in pg_class to the new
cluster.  This is just another example of why.
        regards, tom lane