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

src/backend/tcop/Makefile

@@ -13,6 +13,7 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = \
+	cmdtag.o \
 	dest.o \
 	fastpath.o \
 	postgres.o \

src/backend/tcop/cmdtag.c

@@ -0,0 +1,98 @@
+/*-------------------------------------------------------------------------
+ *
+ * cmdtag.c
+ *	  Data and routines for commandtag names and enumeration.
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/tcop/cmdtag.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "miscadmin.h"
+#include "tcop/cmdtag.h"
+
+
+typedef struct CommandTagBehavior
+{
+	const char *name;
+	const bool	event_trigger_ok;
+	const bool	table_rewrite_ok;
+	const bool	display_rowcount;
+} CommandTagBehavior;
+
+#define PG_CMDTAG(tag, name, evtrgok, rwrok, rowcnt) \
+	{ name, evtrgok, rwrok, rowcnt },
+
+const CommandTagBehavior tag_behavior[COMMAND_TAG_NEXTTAG] = {
+#include "tcop/cmdtaglist.h"
+};
+
+#undef PG_CMDTAG
+
+void
+InitializeQueryCompletion(QueryCompletion *qc)
+{
+	qc->commandTag = CMDTAG_UNKNOWN;
+	qc->nprocessed = 0;
+}
+
+const char *
+GetCommandTagName(CommandTag commandTag)
+{
+	return tag_behavior[commandTag].name;
+}
+
+bool
+command_tag_display_rowcount(CommandTag commandTag)
+{
+	return tag_behavior[commandTag].display_rowcount;
+}
+
+bool
+command_tag_event_trigger_ok(CommandTag commandTag)
+{
+	return tag_behavior[commandTag].event_trigger_ok;
+}
+
+bool
+command_tag_table_rewrite_ok(CommandTag commandTag)
+{
+	return tag_behavior[commandTag].table_rewrite_ok;
+}
+
+/*
+ * Search CommandTag by name
+ *
+ * Returns CommandTag, or CMDTAG_UNKNOWN if not recognized
+ */
+CommandTag
+GetCommandTagEnum(const char *commandname)
+{
+	const CommandTagBehavior *base,
+			   *last,
+			   *position;
+	int			result;
+
+	if (commandname == NULL || *commandname == '\0')
+		return CMDTAG_UNKNOWN;
+
+	base = tag_behavior;
+	last = tag_behavior + lengthof(tag_behavior) - 1;
+	while (last >= base)
+	{
+		position = base + ((last - base) >> 1);
+		result = pg_strcasecmp(commandname, position->name);
+		if (result == 0)
+			return (CommandTag) (position - tag_behavior);
+		else if (result < 0)
+			last = position - 1;
+		else
+			base = position + 1;
+	}
+	return CMDTAG_UNKNOWN;
+}

src/backend/tcop/dest.c

@@ -100,7 +100,7 @@ DestReceiver *None_Receiver = (DestReceiver *) &donothingDR;
  * ----------------
  */
 void
-BeginCommand(const char *commandTag, CommandDest dest)
+BeginCommand(CommandTag commandTag, CommandDest dest)
 {
 	/* Nothing to do at present */
 }
@@ -163,8 +163,12 @@ CreateDestReceiver(CommandDest dest)
  * ----------------
  */
 void
-EndCommand(const char *commandTag, CommandDest dest)
+EndCommand(const QueryCompletion *qc, CommandDest dest, bool force_undecorated_output)
 {
+	char		completionTag[COMPLETION_TAG_BUFSIZE];
+	CommandTag	tag;
+	const char *tagname;
+
 	switch (dest)
 	{
 		case DestRemote:
@@ -172,11 +176,27 @@ EndCommand(const char *commandTag, CommandDest dest)
 		case DestRemoteSimple:
 
 			/*
-			 * We assume the commandTag is plain ASCII and therefore requires
-			 * no encoding conversion.
+			 * We assume the tagname is plain ASCII and therefore requires no
+			 * encoding conversion.
+			 *
+			 * We no longer display LastOid, but to preserve the wire
+			 * protocol, we write InvalidOid where the LastOid used to be
+			 * written.
+			 *
+			 * All cases where LastOid was written also write nprocessed
+			 * count, so just Assert that rather than having an extra test.
 			 */
-			pq_putmessage('C', commandTag, strlen(commandTag) + 1);
-			break;
+			tag = qc->commandTag;
+			tagname = GetCommandTagName(tag);
+
+			if (command_tag_display_rowcount(tag) && !force_undecorated_output)
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+						 tag == CMDTAG_INSERT ?
+						 "%s 0 " UINT64_FORMAT : "%s " UINT64_FORMAT,
+						 tagname, qc->nprocessed);
+			else
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE, "%s", tagname);
+			pq_putmessage('C', completionTag, strlen(completionTag) + 1);
 
 		case DestNone:
 		case DestDebug:

src/backend/tcop/postgres.c

@@ -1064,8 +1064,8 @@ exec_simple_query(const char *query_string)
 	{
 		RawStmt    *parsetree = lfirst_node(RawStmt, parsetree_item);
 		bool		snapshot_set = false;
-		const char *commandTag;
-		char		completionTag[COMPLETION_TAG_BUFSIZE];
+		CommandTag	commandTag;
+		QueryCompletion qc;
 		MemoryContext per_parsetree_context = NULL;
 		List	   *querytree_list,
 				   *plantree_list;
@@ -1081,7 +1081,7 @@ exec_simple_query(const char *query_string)
 		 */
 		commandTag = CreateCommandTag(parsetree->stmt);
 
-		set_ps_display(commandTag, false);
+		set_ps_display(GetCommandTagName(commandTag), false);
 
 		BeginCommand(commandTag, dest);
 
@@ -1239,7 +1239,7 @@ exec_simple_query(const char *query_string)
 						 true,
 						 receiver,
 						 receiver,
-						 completionTag);
+						 &qc);
 
 		receiver->rDestroy(receiver);
 
@@ -1290,7 +1290,7 @@ exec_simple_query(const char *query_string)
 		 * command the client sent, regardless of rewriting. (But a command
 		 * aborted by error will not send an EndCommand report at all.)
 		 */
-		EndCommand(completionTag, dest);
+		EndCommand(&qc, dest, false);
 
 		/* Now we may drop the per-parsetree context, if one was created. */
 		if (per_parsetree_context)
@@ -1352,7 +1352,6 @@ exec_parse_message(const char *query_string,	/* string to execute */
 	MemoryContext oldcontext;
 	List	   *parsetree_list;
 	RawStmt    *raw_parse_tree;
-	const char *commandTag;
 	List	   *querytree_list;
 	CachedPlanSource *psrc;
 	bool		is_named;
@@ -1438,11 +1437,6 @@ exec_parse_message(const char *query_string,	/* string to execute */
 
 		raw_parse_tree = linitial_node(RawStmt, parsetree_list);
 
-		/*
-		 * Get the command name for possible use in status display.
-		 */
-		commandTag = CreateCommandTag(raw_parse_tree->stmt);
-
 		/*
 		 * If we are in an aborted transaction, reject all commands except
 		 * COMMIT/ROLLBACK.  It is important that this test occur before we
@@ -1463,7 +1457,8 @@ exec_parse_message(const char *query_string,	/* string to execute */
 		 * Create the CachedPlanSource before we do parse analysis, since it
 		 * needs to see the unmodified raw parse tree.
 		 */
-		psrc = CreateCachedPlan(raw_parse_tree, query_string, commandTag);
+		psrc = CreateCachedPlan(raw_parse_tree, query_string,
+								CreateCommandTag(raw_parse_tree->stmt));
 
 		/*
 		 * Set up a snapshot if parse analysis will need one.
@@ -1514,8 +1509,8 @@ exec_parse_message(const char *query_string,	/* string to execute */
 	{
 		/* Empty input string.  This is legal. */
 		raw_parse_tree = NULL;
-		commandTag = NULL;
-		psrc = CreateCachedPlan(raw_parse_tree, query_string, commandTag);
+		psrc = CreateCachedPlan(raw_parse_tree, query_string,
+								CMDTAG_UNKNOWN);
 		querytree_list = NIL;
 	}
 
@@ -2031,7 +2026,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 	DestReceiver *receiver;
 	Portal		portal;
 	bool		completed;
-	char		completionTag[COMPLETION_TAG_BUFSIZE];
+	QueryCompletion qc;
 	const char *sourceText;
 	const char *prepStmtName;
 	ParamListInfo portalParams;
@@ -2058,7 +2053,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 	 * If the original query was a null string, just return
 	 * EmptyQueryResponse.
 	 */
-	if (portal->commandTag == NULL)
+	if (portal->commandTag == CMDTAG_UNKNOWN)
 	{
 		Assert(portal->stmts == NIL);
 		NullCommand(dest);
@@ -2104,7 +2099,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 
 	pgstat_report_activity(STATE_RUNNING, sourceText);
 
-	set_ps_display(portal->commandTag, false);
+	set_ps_display(GetCommandTagName(portal->commandTag), false);
 
 	if (save_log_statement_stats)
 		ResetUsage();
@@ -2185,7 +2180,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 						  !execute_is_fetch && max_rows == FETCH_ALL,
 						  receiver,
 						  receiver,
-						  completionTag);
+						  &qc);
 
 	receiver->rDestroy(receiver);
 
@@ -2218,7 +2213,7 @@ exec_execute_message(const char *portal_name, long max_rows)
 		}
 
 		/* Send appropriate CommandComplete to client */
-		EndCommand(completionTag, dest);
+		EndCommand(&qc, dest, false);
 	}
 	else
 	{

src/backend/tcop/pquery.c

@@ -40,7 +40,7 @@ static void ProcessQuery(PlannedStmt *plan,
 						 ParamListInfo params,
 						 QueryEnvironment *queryEnv,
 						 DestReceiver *dest,
-						 char *completionTag);
+						 QueryCompletion *qc);
 static void FillPortalStore(Portal portal, bool isTopLevel);
 static uint64 RunFromStore(Portal portal, ScanDirection direction, uint64 count,
 						   DestReceiver *dest);
@@ -48,11 +48,11 @@ static uint64 PortalRunSelect(Portal portal, bool forward, long count,
 							  DestReceiver *dest);
 static void PortalRunUtility(Portal portal, PlannedStmt *pstmt,
 							 bool isTopLevel, bool setHoldSnapshot,
-							 DestReceiver *dest, char *completionTag);
+							 DestReceiver *dest, QueryCompletion *qc);
 static void PortalRunMulti(Portal portal,
 						   bool isTopLevel, bool setHoldSnapshot,
 						   DestReceiver *dest, DestReceiver *altdest,
-						   char *completionTag);
+						   QueryCompletion *qc);
 static uint64 DoPortalRunFetch(Portal portal,
 							   FetchDirection fdirection,
 							   long count,
@@ -125,10 +125,9 @@ FreeQueryDesc(QueryDesc *qdesc)
  *	sourceText: the source text of the query
  *	params: any parameters needed
  *	dest: where to send results
- *	completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE
- *		in which to store a command completion status string.
+ *	qc: where to store the command completion status data.
  *
- * completionTag may be NULL if caller doesn't want a status string.
+ * qc may be NULL if caller doesn't want a status string.
  *
  * Must be called in a memory context that will be reset or deleted on
  * error; otherwise the executor's memory usage will be leaked.
@@ -139,7 +138,7 @@ ProcessQuery(PlannedStmt *plan,
 			 ParamListInfo params,
 			 QueryEnvironment *queryEnv,
 			 DestReceiver *dest,
-			 char *completionTag)
+			 QueryCompletion *qc)
 {
 	QueryDesc  *queryDesc;
 
@@ -161,38 +160,26 @@ ProcessQuery(PlannedStmt *plan,
 	ExecutorRun(queryDesc, ForwardScanDirection, 0L, true);
 
 	/*
-	 * Build command completion status string, if caller wants one.
+	 * Build command completion status data, if caller wants one.
 	 */
-	if (completionTag)
+	if (qc)
 	{
-		Oid			lastOid;
-
 		switch (queryDesc->operation)
 		{
 			case CMD_SELECT:
-				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-						 "SELECT " UINT64_FORMAT,
-						 queryDesc->estate->es_processed);
+				SetQueryCompletion(qc, CMDTAG_SELECT, queryDesc->estate->es_processed);
 				break;
 			case CMD_INSERT:
-				/* lastoid doesn't exist anymore */
-				lastOid = InvalidOid;
-				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-						 "INSERT %u " UINT64_FORMAT,
-						 lastOid, queryDesc->estate->es_processed);
+				SetQueryCompletion(qc, CMDTAG_INSERT, queryDesc->estate->es_processed);
 				break;
 			case CMD_UPDATE:
-				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-						 "UPDATE " UINT64_FORMAT,
-						 queryDesc->estate->es_processed);
+				SetQueryCompletion(qc, CMDTAG_UPDATE, queryDesc->estate->es_processed);
 				break;
 			case CMD_DELETE:
-				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-						 "DELETE " UINT64_FORMAT,
-						 queryDesc->estate->es_processed);
+				SetQueryCompletion(qc, CMDTAG_DELETE, queryDesc->estate->es_processed);
 				break;
 			default:
-				strcpy(completionTag, "???");
+				SetQueryCompletion(qc, CMDTAG_UNKNOWN, queryDesc->estate->es_processed);
 				break;
 		}
 	}
@@ -675,9 +662,8 @@ PortalSetResultFormat(Portal portal, int nFormats, int16 *formats)
  *
  * altdest: where to send output of non-primary queries
  *
- * completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE
- *		in which to store a command completion status string.
- *		May be NULL if caller doesn't want a status string.
+ * qc: where to store command completion status data.
+ *		May be NULL if caller doesn't want status data.
  *
  * Returns true if the portal's execution is complete, false if it was
  * suspended due to exhaustion of the count parameter.
@@ -685,7 +671,7 @@ PortalSetResultFormat(Portal portal, int nFormats, int16 *formats)
 bool
 PortalRun(Portal portal, long count, bool isTopLevel, bool run_once,
 		  DestReceiver *dest, DestReceiver *altdest,
-		  char *completionTag)
+		  QueryCompletion *qc)
 {
 	bool		result;
 	uint64		nprocessed;
@@ -700,9 +686,9 @@ PortalRun(Portal portal, long count, bool isTopLevel, bool run_once,
 
 	TRACE_POSTGRESQL_QUERY_EXECUTE_START();
 
-	/* Initialize completion tag to empty string */
-	if (completionTag)
-		completionTag[0] = '\0';
+	/* Initialize empty completion data */
+	if (qc)
+		InitializeQueryCompletion(qc);
 
 	if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
 	{
@@ -771,16 +757,13 @@ PortalRun(Portal portal, long count, bool isTopLevel, bool run_once,
 
 				/*
 				 * If the portal result contains a command tag and the caller
-				 * gave us a pointer to store it, copy it. Patch the "SELECT"
-				 * tag to also provide the rowcount.
+				 * gave us a pointer to store it, copy it and update the
+				 * rowcount.
 				 */
-				if (completionTag && portal->commandTag)
+				if (qc && portal->qc.commandTag != CMDTAG_UNKNOWN)
 				{
-					if (strcmp(portal->commandTag, "SELECT") == 0)
-						snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
-								 "SELECT " UINT64_FORMAT, nprocessed);
-					else
-						strcpy(completionTag, portal->commandTag);
+					CopyQueryCompletion(qc, &portal->qc);
+					qc->nprocessed = nprocessed;
 				}
 
 				/* Mark portal not active */
@@ -794,7 +777,7 @@ PortalRun(Portal portal, long count, bool isTopLevel, bool run_once,
 
 			case PORTAL_MULTI_QUERY:
 				PortalRunMulti(portal, isTopLevel, false,
-							   dest, altdest, completionTag);
+							   dest, altdest, qc);
 
 				/* Prevent portal's commands from being re-executed */
 				MarkPortalDone(portal);
@@ -1005,8 +988,9 @@ static void
 FillPortalStore(Portal portal, bool isTopLevel)
 {
 	DestReceiver *treceiver;
-	char		completionTag[COMPLETION_TAG_BUFSIZE];
+	QueryCompletion qc;
 
+	InitializeQueryCompletion(&qc);
 	PortalCreateHoldStore(portal);
 	treceiver = CreateDestReceiver(DestTuplestore);
 	SetTuplestoreDestReceiverParams(treceiver,
@@ -1014,8 +998,6 @@ FillPortalStore(Portal portal, bool isTopLevel)
 									portal->holdContext,
 									false);
 
-	completionTag[0] = '\0';
-
 	switch (portal->strategy)
 	{
 		case PORTAL_ONE_RETURNING:
@@ -1028,12 +1010,12 @@ FillPortalStore(Portal portal, bool isTopLevel)
 			 * portal's holdSnapshot to the snapshot used (or a copy of it).
 			 */
 			PortalRunMulti(portal, isTopLevel, true,
-						   treceiver, None_Receiver, completionTag);
+						   treceiver, None_Receiver, &qc);
 			break;
 
 		case PORTAL_UTIL_SELECT:
 			PortalRunUtility(portal, linitial_node(PlannedStmt, portal->stmts),
-							 isTopLevel, true, treceiver, completionTag);
+							 isTopLevel, true, treceiver, &qc);
 			break;
 
 		default:
@@ -1042,9 +1024,9 @@ FillPortalStore(Portal portal, bool isTopLevel)
 			break;
 	}
 
-	/* Override default completion tag with actual command result */
-	if (completionTag[0] != '\0')
-		portal->commandTag = pstrdup(completionTag);
+	/* Override portal completion data with actual command results */
+	if (qc.commandTag != CMDTAG_UNKNOWN)
+		CopyQueryCompletion(&portal->qc, &qc);
 
 	treceiver->rDestroy(treceiver);
 }
@@ -1130,7 +1112,7 @@ RunFromStore(Portal portal, ScanDirection direction, uint64 count,
 static void
 PortalRunUtility(Portal portal, PlannedStmt *pstmt,
 				 bool isTopLevel, bool setHoldSnapshot,
-				 DestReceiver *dest, char *completionTag)
+				 DestReceiver *dest, QueryCompletion *qc)
 {
 	Node	   *utilityStmt = pstmt->utilityStmt;
 	Snapshot	snapshot;
@@ -1178,7 +1160,7 @@ PortalRunUtility(Portal portal, PlannedStmt *pstmt,
 				   portal->portalParams,
 				   portal->queryEnv,
 				   dest,
-				   completionTag);
+				   qc);
 
 	/* Some utility statements may change context on us */
 	MemoryContextSwitchTo(portal->portalContext);
@@ -1202,7 +1184,7 @@ static void
 PortalRunMulti(Portal portal,
 			   bool isTopLevel, bool setHoldSnapshot,
 			   DestReceiver *dest, DestReceiver *altdest,
-			   char *completionTag)
+			   QueryCompletion *qc)
 {
 	bool		active_snapshot_set = false;
 	ListCell   *stmtlist_item;
@@ -1284,7 +1266,7 @@ PortalRunMulti(Portal portal,
 							 portal->sourceText,
 							 portal->portalParams,
 							 portal->queryEnv,
-							 dest, completionTag);
+							 dest, qc);
 			}
 			else
 			{
@@ -1319,7 +1301,7 @@ PortalRunMulti(Portal portal,
 				Assert(!active_snapshot_set);
 				/* statement can set tag string */
 				PortalRunUtility(portal, pstmt, isTopLevel, false,
-								 dest, completionTag);
+								 dest, qc);
 			}
 			else
 			{
@@ -1350,8 +1332,8 @@ PortalRunMulti(Portal portal,
 		PopActiveSnapshot();
 
 	/*
-	 * If a command completion tag was supplied, use it.  Otherwise use the
-	 * portal's commandTag as the default completion tag.
+	 * If a query completion data was supplied, use it.  Otherwise use the
+	 * portal's query completion data.
 	 *
 	 * Exception: Clients expect INSERT/UPDATE/DELETE tags to have counts, so
 	 * fake them with zeros.  This can happen with DO INSTEAD rules if there
@@ -1361,18 +1343,12 @@ PortalRunMulti(Portal portal,
 	 * e.g.  an INSERT that does an UPDATE instead should not print "0 1" if
 	 * one row was updated.  See QueryRewrite(), step 3, for details.
 	 */
-	if (completionTag && completionTag[0] == '\0')
+	if (qc && qc->commandTag == CMDTAG_UNKNOWN)
 	{
-		if (portal->commandTag)
-			strcpy(completionTag, portal->commandTag);
-		if (strcmp(completionTag, "SELECT") == 0)
-			sprintf(completionTag, "SELECT 0 0");
-		else if (strcmp(completionTag, "INSERT") == 0)
-			strcpy(completionTag, "INSERT 0 0");
-		else if (strcmp(completionTag, "UPDATE") == 0)
-			strcpy(completionTag, "UPDATE 0");
-		else if (strcmp(completionTag, "DELETE") == 0)
-			strcpy(completionTag, "DELETE 0");
+		if (portal->qc.commandTag != CMDTAG_UNKNOWN)
+			CopyQueryCompletion(qc, &portal->qc);
+		/* If the caller supplied a qc, we should have set it by now. */
+		Assert(qc->commandTag != CMDTAG_UNKNOWN);
 	}
 }