Re: pgsql-server/ oc/src/sgml/runtime.sgml rc/back ...

Christopher Kings-Lynne wrote:
> > Log message:
> >     Finish implementation of hashed aggregation.  Add enable_hashagg GUC
> >     parameter to allow it to be forced off for comparison purposes.
> >     Add ORDER BY clauses to a bunch of regression test queries that will
> >     otherwise produce randomly-ordered output in the new regime.
>
> Out of interest (since I was away while this was proposed I assume),
> what's the idea with hashed aggergation?  I assume each group is now in a
> hash bucket?  How did it work before?

It sequential scanned the group of possible matches.  How it hashes the
value and looks for matches that way --- much faster and the way most
db's do it.

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