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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