Re: Hash support for grouping sets

>>>>> "Mark" == Mark Dilger <hornschnorter@gmail.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)