Re: [HACKERS] Performance degradation in TPC-H Q18

On Mon, Mar 6, 2017 at 5:19 PM, Andres Freund <andres@anarazel.de> wrote:
> The whole performance issue trigger this thread only exists when the
> hashtable sizes are mis-estimated, right?  Turns out that after applying
> the just-committed changes, that "fixing" the bad-mixing and/or doing
> iteration that's not entirely in hash-order, slighty degrades
> performance.  The difference is that without either of those additional
> changes, we resize to the "right" size very early, when the hashtable is
> barely filled (i.e. only few entries need to be moved), because the
> imbalance is observed at tsart.  With the changes however the resizing
> happens when the table is pretty full (i.e. a lot of entries need to be
> moved).  So the early imbalance ends up actually not hurting
> performance...

Hmm.  I don't know what to do about that.

-- 
Robert Haas
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