Fix representation of SORT_TYPE_STILL_IN_PROGRESS.

It turns out that the code did indeed rely on a zeroed
TuplesortInstrumentation.sortMethod field to indicate
"this worker never did anything", although it seems the
issue only comes up during certain race-condition-y cases.

Hence, rearrange the TuplesortMethod enum to restore
SORT_TYPE_STILL_IN_PROGRESS to having the value zero,
and add some comments reinforcing that that isn't optional.

Also future-proof a loop over the possible values of the enum.
sizeof(bits32) happened to be the correct limit value,
but only by purest coincidence.

Per buildfarm and local investigation.

Discussion: https://postgr.es/m/12222.1586223974@sss.pgh.pa.us

1 files changed, 5 insertions, 5 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index cad10662bb0..baaa5817af7 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -2762,14 +2762,14 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
 	List	   *methodNames = NIL;
 
 	/* Generate a list of sort methods used across all groups. */
-	for (int bit = 0; bit < sizeof(bits32); ++bit)
+	for (int bit = 0; bit < NUM_TUPLESORTMETHODS; bit++)
 	{
-		if (groupInfo->sortMethods & (1 << bit))
+		TuplesortMethod sortMethod = (1 << bit);
+
+		if (groupInfo->sortMethods & sortMethod)
 		{
-			TuplesortMethod sortMethod = (1 << bit);
-			const char *methodName;
+			const char *methodName = tuplesort_method_name(sortMethod);
 
-			methodName = tuplesort_method_name(sortMethod);
 			methodNames = lappend(methodNames, unconstify(char *, methodName));
 		}
 	}