Represent command completion tags as structs

The backend was using strings to represent command tags and doing string
comparisons in multiple places, but that's slow and unhelpful.  Create a
new command list with a supporting structure to use instead; this is
stored in a tag-list-file that can be tailored to specific purposes with
a caller-definable C macro, similar to what we do for WAL resource
managers.  The first first such uses are a new CommandTag enum and a
CommandTagBehavior struct.

Replace numerous occurrences of char *completionTag with a
QueryCompletion struct so that the code no longer stores information
about completed queries in a cstring.  Only at the last moment, in
EndCommand(), does this get converted to a string.

EventTriggerCacheItem no longer holds an array of palloc’d tag strings
in sorted order, but rather just a Bitmapset over the CommandTags.

Author: Mark Dilger, with unsolicited help from Álvaro Herrera
Reviewed-by: John Naylor, Tom Lane
Discussion: https://postgr.es/m/981A9DB4-3F0C-4DA5-88AD-CB9CFF4D6CAD@enterprisedb.com

2 files changed, 20 insertions, 18 deletions

diff --git a/src/backend/utils/cache/evtcache.c b/src/backend/utils/cache/evtcache.c
index 1b63048a774..b9c1a0a5adb 100644
--- a/src/backend/utils/cache/evtcache.c
+++ b/src/backend/utils/cache/evtcache.c
@@ -20,6 +20,7 @@
 #include "catalog/pg_event_trigger.h"
 #include "catalog/pg_type.h"
 #include "commands/trigger.h"
+#include "tcop/cmdtag.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/catcache.h"
@@ -51,7 +52,7 @@ static EventTriggerCacheStateType EventTriggerCacheState = ETCS_NEEDS_REBUILD;
 static void BuildEventTriggerCache(void);
 static void InvalidateEventCacheCallback(Datum arg,
 										 int cacheid, uint32 hashvalue);
-static int	DecodeTextArrayToCString(Datum array, char ***cstringp);
+static Bitmapset *DecodeTextArrayToBitmapset(Datum array);
 
 /*
  * Search the event cache by trigger event.
@@ -180,10 +181,7 @@ BuildEventTriggerCache(void)
 		evttags = heap_getattr(tup, Anum_pg_event_trigger_evttags,
 							   RelationGetDescr(rel), &evttags_isnull);
 		if (!evttags_isnull)
-		{
-			item->ntags = DecodeTextArrayToCString(evttags, &item->tag);
-			qsort(item->tag, item->ntags, sizeof(char *), pg_qsort_strcmp);
-		}
+			item->tagset = DecodeTextArrayToBitmapset(evttags);
 
 		/* Add to cache entry. */
 		entry = hash_search(cache, &event, HASH_ENTER, &found);
@@ -215,18 +213,18 @@ BuildEventTriggerCache(void)
 }
 
 /*
- * Decode text[] to an array of C strings.
+ * Decode text[] to a Bitmapset of CommandTags.
  *
  * We could avoid a bit of overhead here if we were willing to duplicate some
  * of the logic from deconstruct_array, but it doesn't seem worth the code
  * complexity.
  */
-static int
-DecodeTextArrayToCString(Datum array, char ***cstringp)
+static Bitmapset *
+DecodeTextArrayToBitmapset(Datum array)
 {
 	ArrayType  *arr = DatumGetArrayTypeP(array);
 	Datum	   *elems;
-	char	  **cstring;
+	Bitmapset  *bms;
 	int			i;
 	int			nelems;
 
@@ -234,13 +232,17 @@ DecodeTextArrayToCString(Datum array, char ***cstringp)
 		elog(ERROR, "expected 1-D text array");
 	deconstruct_array(arr, TEXTOID, -1, false, 'i', &elems, NULL, &nelems);
 
-	cstring = palloc(nelems * sizeof(char *));
-	for (i = 0; i < nelems; ++i)
-		cstring[i] = TextDatumGetCString(elems[i]);
+	for (bms = NULL, i = 0; i < nelems; ++i)
+	{
+		char	   *str = TextDatumGetCString(elems[i]);
+
+		bms = bms_add_member(bms, GetCommandTagEnum(str));
+		pfree(str);
+	}
 
 	pfree(elems);
-	*cstringp = cstring;
-	return nelems;
+
+	return bms;
 }
 
 /*
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index c47be0ba4cd..dbae18d68c6 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -158,12 +158,12 @@ InitPlanCache(void)
  *
  * raw_parse_tree: output of raw_parser(), or NULL if empty query
  * query_string: original query text
- * commandTag: compile-time-constant tag for query, or NULL if empty query
+ * commandTag: command tag for query, or UNKNOWN if empty query
  */
 CachedPlanSource *
 CreateCachedPlan(RawStmt *raw_parse_tree,
 				 const char *query_string,
-				 const char *commandTag)
+				 CommandTag commandTag)
 {
 	CachedPlanSource *plansource;
 	MemoryContext source_context;
@@ -241,12 +241,12 @@ CreateCachedPlan(RawStmt *raw_parse_tree,
  *
  * raw_parse_tree: output of raw_parser(), or NULL if empty query
  * query_string: original query text
- * commandTag: compile-time-constant tag for query, or NULL if empty query
+ * commandTag: command tag for query, or NULL if empty query
  */
 CachedPlanSource *
 CreateOneShotCachedPlan(RawStmt *raw_parse_tree,
 						const char *query_string,
-						const char *commandTag)
+						CommandTag commandTag)
 {
 	CachedPlanSource *plansource;