Re: vacuum, performance, and MVCC

> > You mean systems that are designed so exactly, that they can't take 10%
> > performance change ?
>
> No, that's not really the point, performance degrades over time, in one
> minute it degraded 10%.
>
> The update to session ratio has a HUGE impact on PostgreSQL. If you have a
> thousand active sessions, it may take a minute to degrade 10% assuming
> some level of active vs operations per session per action.

So don't do an update. Multiple updates to the same row block anyway
which is generally not something you want anyway.

If you INSERT into multiple partitions (by time -- say one per minute)
and TRUNCATE periodically (30 minute old partitions for 30 minute
expiry) it works much better. Expiring the session is quite fast as well
since they'll go away with the truncate.

Index on sessionid and time and grab the row with the most recent time.
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