Re: Turning off HOT/Cleanup sometimes

On Wed, Jan 15, 2014 at 5:14 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> We already know that HOT is ineffective in areas of high contention
> (previous thread by me). Prior experience was that smaller tables
> didn't show much apparent benefit from using HOT either; its
> effectiveness was limited to medium and large tables being updated.
> The two already stated use cases that would apply are these ones

Do you have a link to that previous thread? I don't happen to recall
that conversation.

I've found that HOT can be very important on smaller tables, so I'm
skeptical of that as a general conclusion. What I think might be true
is that if VACUUM is going to hit the table often enough to make you
happy, then you don't really need HOT. In other words, if the update
rate is non-zero but low, not too much cruft will accumulate before
the table gets vacuumed, and you may be OK. If the update rate is
high, though, I think disabling HOT will be painful on a table of any
size. There might be exceptions, but I can't think of what the are
off-hand.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company