Re: HashAgg's batching counter starts at 0, but Hash's starts at 1.

On Wed, Jul 29, 2020 at 08:35:08PM -0700, Peter Geoghegan wrote:
> AFAICT sort (and IncrSort) don't fail to show a field value if it is
> zero. Rather, they consistently show "space used" (in non-text
> format), which can be either memory or disk space. Technically they
> don't violate the letter of the law that you cite. (Though admittedly
> this is a legalistic loophole -- the "space" value presumably has to
> be interpreted according to different rules for programs that consume
> non-text EXPLAIN output.)

Sort shows this:
Sort Method: "external merge" +
Sort Space Used: 19520 +
Sort Space Type: "Disk" +

Incremental sort shows this:
Sort Methods Used: +
- "external merge" +
Sort Space Disk: +
Average Sort Space Used: 128+
Peak Sort Space Used: 128 +

So my 2ndary suggestion is to conditionalize based on the method rather than
value of space used.

--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -2830 +2830 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
- if (groupInfo->maxMemorySpaceUsed > 0)
+ if (groupInfo->sortMethods & SORT_TYPE_QUICKSORT)
@@ -2847 +2847 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
- if (groupInfo->maxDiskSpaceUsed > 0)
+ if (groupInfo->sortMethods & SORT_TYPE_EXTERNAL_SORT)

--
Justin