Re: Hash support for grouping sets

>>>>> "Mark" == Mark Dilger <hornschnorter(at)gmail(dot)com> writes:

Mark> Hi Andrew,

Mark> Reviewing the patch a bit more, I find it hard to understand the
Mark> comment about passing -1 as a flag for finalize_aggregates. Any
Mark> chance you can spend a bit more time word-smithing that code
Mark> comment?

Sure.

How does this look for wording (I'll incorporate it into an updated
patch later):

/*
* Compute the final value of all aggregates for one group.
*
* This function handles only one grouping set at a time. But in the hash
* case, it's the caller's responsibility to have selected the set already, and
* we pass in -1 as currentSet here to flag that; this also changes how we
* handle the indexing into AggStatePerGroup as explained below.
*
* Results are stored in the output econtext aggvalues/aggnulls.
*/
static void
finalize_aggregates(AggState *aggstate,
AggStatePerAgg peraggs,
AggStatePerGroup pergroup,
int currentSet)
{
ExprContext *econtext = aggstate->ss.ps.ps_ExprContext;
Datum *aggvalues = econtext->ecxt_aggvalues;
bool *aggnulls = econtext->ecxt_aggnulls;
int aggno;
int transno;

/*
* If currentSet >= 0, then we're doing sorted grouping, and pergroup is an
* array of size numTrans*numSets which we have to index into using
* currentSet in addition to transno. The caller may not have selected the
* set, so we do that.
*
* If currentSet < 0, then we're doing hashed grouping, and pergroup is an
* array of only numTrans items (since for hashed grouping, each grouping
* set is in a separate hashtable). We rely on the caller having done
* select_current_set, and we fudge currentSet to 0 in order to make the
* same indexing calculations work as for the grouping case.
*/
if (currentSet >= 0)
select_current_set(aggstate, currentSet, false);
else
currentSet = 0;

--
Andrew (irc:RhodiumToad)