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

Author: alvherre

contrib/pg_stat_statements/pg_stat_statements.c

@@ -307,7 +307,7 @@ static void pgss_ExecutorEnd(QueryDesc *queryDesc);
 static void pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 								ProcessUtilityContext context, ParamListInfo params,
 								QueryEnvironment *queryEnv,
-								DestReceiver *dest, char *completionTag);
+								DestReceiver *dest, QueryCompletion *qc);
 static uint64 pgss_hash_string(const char *str, int len);
 static void pgss_store(const char *query, uint64 queryId,
 					   int query_location, int query_len,
@@ -960,7 +960,7 @@ static void
 pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 					ProcessUtilityContext context,
 					ParamListInfo params, QueryEnvironment *queryEnv,
-					DestReceiver *dest, char *completionTag)
+					DestReceiver *dest, QueryCompletion *qc)
 {
 	Node	   *parsetree = pstmt->utilityStmt;
 
@@ -998,11 +998,11 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 			if (prev_ProcessUtility)
 				prev_ProcessUtility(pstmt, queryString,
 									context, params, queryEnv,
-									dest, completionTag);
+									dest, qc);
 			else
 				standard_ProcessUtility(pstmt, queryString,
 										context, params, queryEnv,
-										dest, completionTag);
+										dest, qc);
 		}
 		PG_FINALLY();
 		{
@@ -1013,12 +1013,8 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 		INSTR_TIME_SET_CURRENT(duration);
 		INSTR_TIME_SUBTRACT(duration, start);
 
-		/* parse command tag to retrieve the number of affected rows. */
-		if (completionTag &&
-			strncmp(completionTag, "COPY ", 5) == 0)
-			rows = pg_strtouint64(completionTag + 5, NULL, 10);
-		else
-			rows = 0;
+		if (qc)
+			rows = qc->commandTag == CMDTAG_COPY ? qc->nprocessed : 0;
 
 		/* calc differences of buffer counters. */
 		bufusage.shared_blks_hit =
@@ -1060,11 +1056,11 @@ pgss_ProcessUtility(PlannedStmt *pstmt, const char *queryString,
 		if (prev_ProcessUtility)
 			prev_ProcessUtility(pstmt, queryString,
 								context, params, queryEnv,
-								dest, completionTag);
+								dest, qc);
 		else
 			standard_ProcessUtility(pstmt, queryString,
 									context, params, queryEnv,
-									dest, completionTag);
+									dest, qc);
 	}
 }
 

contrib/sepgsql/hooks.c

@@ -317,7 +317,7 @@ sepgsql_utility_command(PlannedStmt *pstmt,
 						ParamListInfo params,
 						QueryEnvironment *queryEnv,
 						DestReceiver *dest,
-						char *completionTag)
+						QueryCompletion *qc)
 {
 	Node	   *parsetree = pstmt->utilityStmt;
 	sepgsql_context_info_t saved_context_info = sepgsql_context_info;
@@ -380,11 +380,11 @@ sepgsql_utility_command(PlannedStmt *pstmt,
 		if (next_ProcessUtility_hook)
 			(*next_ProcessUtility_hook) (pstmt, queryString,
 										 context, params, queryEnv,
-										 dest, completionTag);
+										 dest, qc);
 		else
 			standard_ProcessUtility(pstmt, queryString,
 									context, params, queryEnv,
-									dest, completionTag);
+									dest, qc);
 	}
 	PG_FINALLY();
 	{

doc/src/sgml/event-trigger.sgml

@@ -1074,7 +1074,7 @@ typedef struct EventTriggerData
     NodeTag     type;
     const char *event;      /* event name */
     Node       *parsetree;  /* parse tree */
-    const char *tag;        /* command tag */
+    CommandTag  tag;        /* command tag */
 } EventTriggerData;
 </programlisting>
 

src/backend/commands/createas.c

@@ -10,7 +10,7 @@
  *
  * Formerly, CTAS was implemented as a variant of SELECT, which led
  * to assorted legacy behaviors that we still try to preserve, notably that
- * we must return a tuples-processed count in the completionTag.  (We no
+ * we must return a tuples-processed count in the QueryCompletion.  (We no
  * longer do that for CTAS ... WITH NO DATA, however.)
  *
  * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
@@ -225,7 +225,7 @@ create_ctas_nodata(List *tlist, IntoClause *into)
 ObjectAddress
 ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 				  ParamListInfo params, QueryEnvironment *queryEnv,
-				  char *completionTag)
+				  QueryCompletion *qc)
 {
 	Query	   *query = castNode(Query, stmt->query);
 	IntoClause *into = stmt->into;
@@ -270,7 +270,7 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		ExecuteStmt *estmt = castNode(ExecuteStmt, query->utilityStmt);
 
 		Assert(!is_matview);	/* excluded by syntax */
-		ExecuteQuery(pstate, estmt, into, params, dest, completionTag);
+		ExecuteQuery(pstate, estmt, into, params, dest, qc);
 
 		/* get object address that intorel_startup saved for us */
 		address = ((DR_intorel *) dest)->reladdr;
@@ -352,11 +352,9 @@ ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
 		/* run the plan to completion */
 		ExecutorRun(queryDesc, ForwardScanDirection, 0L, true);
 
-		/* save the rowcount if we're given a completionTag to fill */
-		if (completionTag)
-			snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-					 "SELECT " UINT64_FORMAT,
-					 queryDesc->estate->es_processed);
+		/* save the rowcount if we're given a qc to fill */
+		if (qc)
+			SetQueryCompletion(qc, CMDTAG_SELECT, queryDesc->estate->es_processed);
 
 		/* get object address that intorel_startup saved for us */
 		address = ((DR_intorel *) dest)->reladdr;