Custom WAL Resource Managers.

Allow extensions to specify a new custom resource manager (rmgr),
which allows specialized WAL. This is meant to be used by a Table
Access Method or Index Access Method.

Prior to this commit, only Generic WAL was available, which offers
support for recovery and physical replication but not logical
replication.

Reviewed-by: Julien Rouhaud, Bharath Rupireddy, Andres Freund
Discussion: https://postgr.es/m/ed1fb2e22d15d3563ae0eb610f7b61bb15999c0a.camel%40j-davis.com

src/backend/access/transam/rmgr.c

@@ -24,16 +24,138 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "fmgr.h"
+#include "funcapi.h"
+#include "miscadmin.h"
 #include "replication/decode.h"
 #include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
+#include "utils/builtins.h"
 #include "utils/relmapper.h"
 
 /* must be kept in sync with RmgrData definition in xlog_internal.h */
 #define PG_RMGR(symname,name,redo,desc,identify,startup,cleanup,mask,decode) \
 	{ name, redo, desc, identify, startup, cleanup, mask, decode },
 
-const RmgrData RmgrTable[RM_MAX_ID + 1] = {
+RmgrData RmgrTable[RM_MAX_ID + 1] = {
 #include "access/rmgrlist.h"
 };
+
+/*
+ * Start up all resource managers.
+ */
+void
+RmgrStartup(void)
+{
+	for (int rmid = 0; rmid <= RM_MAX_ID; rmid++)
+	{
+		if (!RmgrIdExists(rmid))
+			continue;
+
+		if (RmgrTable[rmid].rm_startup != NULL)
+			RmgrTable[rmid].rm_startup();
+	}
+}
+
+/*
+ * Clean up all resource managers.
+ */
+void
+RmgrCleanup(void)
+{
+	for (int rmid = 0; rmid <= RM_MAX_ID; rmid++)
+	{
+		if (!RmgrIdExists(rmid))
+			continue;
+
+		if (RmgrTable[rmid].rm_cleanup != NULL)
+			RmgrTable[rmid].rm_cleanup();
+	}
+}
+
+/*
+ * Emit ERROR when we encounter a record with an RmgrId we don't
+ * recognize.
+ */
+void
+RmgrNotFound(RmgrId rmid)
+{
+	ereport(ERROR, (errmsg("resource manager with ID %d not registered", rmid),
+					errhint("Include the extension module that implements this resource manager in shared_preload_libraries.")));
+}
+
+/*
+ * Register a new custom WAL resource manager.
+ *
+ * Resource manager IDs must be globally unique across all extensions. Refer
+ * to https://wiki.postgresql.org/wiki/CustomWALResourceManager to reserve a
+ * unique RmgrId for your extension, to avoid conflicts with other extension
+ * developers. During development, use RM_EXPERIMENTAL_ID to avoid needlessly
+ * reserving a new ID.
+ */
+void
+RegisterCustomRmgr(RmgrId rmid, RmgrData *rmgr)
+{
+	if (rmgr->rm_name == NULL || strlen(rmgr->rm_name) == 0)
+		ereport(ERROR, (errmsg("custom resource manager name is invalid"),
+						errhint("Provide a non-empty name for the custom resource manager.")));
+
+	if (!RMID_IS_CUSTOM(rmid))
+		ereport(ERROR, (errmsg("custom resource manager ID %d is out of range", rmid),
+						errhint("Provide a custom resource manager ID between %d and %d.",
+								RM_MIN_CUSTOM_ID, RM_MAX_CUSTOM_ID)));
+
+	if (!process_shared_preload_libraries_in_progress)
+		ereport(ERROR,
+				(errmsg("failed to register custom resource manager \"%s\" with ID %d", rmgr->rm_name, rmid),
+				 errdetail("Custom resource manager must be registered while initializing modules in shared_preload_libraries.")));
+
+	if (RmgrTable[rmid].rm_name != NULL)
+		ereport(ERROR,
+				(errmsg("failed to register custom resource manager \"%s\" with ID %d", rmgr->rm_name, rmid),
+				 errdetail("Custom resource manager \"%s\" already registered with the same ID.",
+						   RmgrTable[rmid].rm_name)));
+
+	/* check for existing rmgr with the same name */
+	for (int existing_rmid = 0; existing_rmid <= RM_MAX_ID; existing_rmid++)
+	{
+		if (!RmgrIdExists(existing_rmid))
+			continue;
+
+		if (!pg_strcasecmp(RmgrTable[existing_rmid].rm_name, rmgr->rm_name))
+			ereport(ERROR,
+				(errmsg("failed to register custom resource manager \"%s\" with ID %d", rmgr->rm_name, rmid),
+				 errdetail("Existing resource manager with ID %d has the same name.", existing_rmid)));
+	}
+
+	/* register it */
+	RmgrTable[rmid] = *rmgr;
+	ereport(LOG,
+			(errmsg("registered custom resource manager \"%s\" with ID %d",
+					rmgr->rm_name, rmid)));
+}
+
+/* SQL SRF showing loaded resource managers */
+Datum
+pg_get_wal_resource_managers(PG_FUNCTION_ARGS)
+{
+#define PG_GET_RESOURCE_MANAGERS_COLS 3
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	Datum		values[PG_GET_RESOURCE_MANAGERS_COLS];
+	bool		nulls[PG_GET_RESOURCE_MANAGERS_COLS] = {0};
+
+	SetSingleFuncCall(fcinfo, 0);
+
+	for (int rmid = 0; rmid <= RM_MAX_ID; rmid++)
+	{
+		if (!RmgrIdExists(rmid))
+			continue;
+		values[0] = Int32GetDatum(rmid);
+		values[1] = CStringGetTextDatum(GetRmgr(rmid).rm_name);
+		values[2] = BoolGetDatum(RMID_IS_BUILTIN(rmid));
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+	}
+
+	return (Datum) 0;
+}

src/backend/access/transam/xlogreader.c

@@ -1102,7 +1102,7 @@ ValidXLogRecordHeader(XLogReaderState *state, XLogRecPtr RecPtr,
 							  (uint32) SizeOfXLogRecord, record->xl_tot_len);
 		return false;
 	}
-	if (record->xl_rmid > RM_MAX_ID)
+	if (!RMID_IS_VALID(record->xl_rmid))
 	{
 		report_invalid_record(state,
 							  "invalid resource manager ID %u at %X/%X",

src/backend/access/transam/xlogrecovery.c

@@ -1541,7 +1541,6 @@ ShutdownWalRecovery(void)
 void
 PerformWalRecovery(void)
 {
-	int			rmid;
 	XLogRecord *record;
 	bool		reachedRecoveryTarget = false;
 	TimeLineID	replayTLI;
@@ -1614,12 +1613,7 @@ PerformWalRecovery(void)
 
 		InRedo = true;
 
-		/* Initialize resource managers */
-		for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
-		{
-			if (RmgrTable[rmid].rm_startup != NULL)
-				RmgrTable[rmid].rm_startup();
-		}
+		RmgrStartup();
 
 		ereport(LOG,
 				(errmsg("redo starts at %X/%X",
@@ -1756,12 +1750,7 @@ PerformWalRecovery(void)
 			}
 		}
 
-		/* Allow resource managers to do any required cleanup. */
-		for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
-		{
-			if (RmgrTable[rmid].rm_cleanup != NULL)
-				RmgrTable[rmid].rm_cleanup();
-		}
+		RmgrCleanup();
 
 		ereport(LOG,
 				(errmsg("redo done at %X/%X system usage: %s",
@@ -1881,7 +1870,7 @@ ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *repl
 		xlogrecovery_redo(xlogreader, *replayTLI);
 
 	/* Now apply the WAL record itself */
-	RmgrTable[record->xl_rmid].rm_redo(xlogreader);
+	GetRmgr(record->xl_rmid).rm_redo(xlogreader);
 
 	/*
 	 * After redo, check whether the backup pages associated with the WAL
@@ -2111,20 +2100,20 @@ rm_redo_error_callback(void *arg)
 void
 xlog_outdesc(StringInfo buf, XLogReaderState *record)
 {
-	RmgrId		rmid = XLogRecGetRmid(record);
+	RmgrData	rmgr = GetRmgr(XLogRecGetRmid(record));
 	uint8		info = XLogRecGetInfo(record);
 	const char *id;
 
-	appendStringInfoString(buf, RmgrTable[rmid].rm_name);
+	appendStringInfoString(buf, rmgr.rm_name);
 	appendStringInfoChar(buf, '/');
 
-	id = RmgrTable[rmid].rm_identify(info);
+	id = rmgr.rm_identify(info);
 	if (id == NULL)
 		appendStringInfo(buf, "UNKNOWN (%X): ", info & ~XLR_INFO_MASK);
 	else
 		appendStringInfo(buf, "%s: ", id);
 
-	RmgrTable[rmid].rm_desc(buf, record);
+	rmgr.rm_desc(buf, record);
 }
 
 #ifdef WAL_DEBUG
@@ -2273,7 +2262,7 @@ getRecordTimestamp(XLogReaderState *record, TimestampTz *recordXtime)
 static void
 verifyBackupPageConsistency(XLogReaderState *record)
 {
-	RmgrId		rmid = XLogRecGetRmid(record);
+	RmgrData	rmgr = GetRmgr(XLogRecGetRmid(record));
 	RelFileNode rnode;
 	ForkNumber	forknum;
 	BlockNumber blkno;
@@ -2353,10 +2342,10 @@ verifyBackupPageConsistency(XLogReaderState *record)
 		 * If masking function is defined, mask both the primary and replay
 		 * images
 		 */
-		if (RmgrTable[rmid].rm_mask != NULL)
+		if (rmgr.rm_mask != NULL)
 		{
-			RmgrTable[rmid].rm_mask(replay_image_masked, blkno);
-			RmgrTable[rmid].rm_mask(primary_image_masked, blkno);
+			rmgr.rm_mask(replay_image_masked, blkno);
+			rmgr.rm_mask(primary_image_masked, blkno);
 		}
 
 		/* Time to compare the primary and replay images. */

src/backend/postmaster/postmaster.c

@@ -1039,6 +1039,12 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	InitializeShmemGUCs();
 
+	/*
+	 * Now that modules have been loaded, we can process any custom resource
+	 * managers specified in the wal_consistency_checking GUC.
+	 */
+	InitializeWalConsistencyChecking();
+
 	/*
 	 * If -C was specified with a runtime-computed GUC, we held off printing
 	 * the value earlier, as the GUC was not yet initialized.  We handle -C

src/backend/replication/logical/decode.c

@@ -94,7 +94,7 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 {
 	XLogRecordBuffer buf;
 	TransactionId txid;
-	RmgrId rmid;
+	RmgrData rmgr;
 
 	buf.origptr = ctx->reader->ReadRecPtr;
 	buf.endptr = ctx->reader->EndRecPtr;
@@ -115,10 +115,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 								 buf.origptr);
 	}
 
-	rmid = XLogRecGetRmid(record);
+	rmgr = GetRmgr(XLogRecGetRmid(record));
 
-	if (RmgrTable[rmid].rm_decode != NULL)
-		RmgrTable[rmid].rm_decode(ctx, &buf);
+	if (rmgr.rm_decode != NULL)
+		rmgr.rm_decode(ctx, &buf);
 	else
 	{
 		/* just deal with xid, and done */

src/backend/utils/init/miscinit.c

@@ -1610,6 +1610,7 @@ char	   *local_preload_libraries_string = NULL;
 
 /* Flag telling that we are loading shared_preload_libraries */
 bool		process_shared_preload_libraries_in_progress = false;
+bool		process_shared_preload_libraries_done = false;
 
 /*
  * load the shared libraries listed in 'libraries'
@@ -1677,6 +1678,7 @@ process_shared_preload_libraries(void)
 				   "shared_preload_libraries",
 				   false);
 	process_shared_preload_libraries_in_progress = false;
+	process_shared_preload_libraries_done = true;
 }
 
 /*

src/backend/utils/misc/guc.c

@@ -245,6 +245,11 @@ static bool check_default_with_oids(bool *newval, void **extra, GucSource source
 static ConfigVariable *ProcessConfigFileInternal(GucContext context,
 												 bool applySettings, int elevel);
 
+/*
+ * Track whether there were any deferred checks for custom resource managers
+ * specified in wal_consistency_checking.
+ */
+static bool check_wal_consistency_checking_deferred = false;
 
 /*
  * Options for enum values defined in this module.
@@ -5835,6 +5840,36 @@ InitializeGUCOptions(void)
 	InitializeGUCOptionsFromEnvironment();
 }
 
+/*
+ * If any custom resource managers were specified in the
+ * wal_consistency_checking GUC, processing was deferred. Now that
+ * shared_preload_libraries have been loaded, process wal_consistency_checking
+ * again.
+ */
+void
+InitializeWalConsistencyChecking(void)
+{
+	Assert(process_shared_preload_libraries_done);
+
+	if (check_wal_consistency_checking_deferred)
+	{
+		struct config_generic *guc;
+
+		guc = find_option("wal_consistency_checking", false, false, ERROR);
+
+		check_wal_consistency_checking_deferred = false;
+
+		set_config_option("wal_consistency_checking",
+						  wal_consistency_checking_string,
+						  PGC_POSTMASTER, guc->source,
+						  GUC_ACTION_SET, true, ERROR, false);
+
+		/* checking should not be deferred again */
+		Assert(!check_wal_consistency_checking_deferred);
+	}
+
+}
+
 /*
  * Assign any GUC values that can come from the server's environment.
  *
@@ -11882,13 +11917,13 @@ check_wal_consistency_checking(char **newval, void **extra, GucSource source)
 	{
 		char	   *tok = (char *) lfirst(l);
 		bool		found = false;
-		RmgrId		rmid;
+		int			rmid;
 
 		/* Check for 'all'. */
 		if (pg_strcasecmp(tok, "all") == 0)
 		{
 			for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
-				if (RmgrTable[rmid].rm_mask != NULL)
+				if (RmgrIdExists(rmid) && GetRmgr(rmid).rm_mask != NULL)
 					newwalconsistency[rmid] = true;
 			found = true;
 		}
@@ -11900,8 +11935,8 @@ check_wal_consistency_checking(char **newval, void **extra, GucSource source)
 			 */
 			for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
 			{
-				if (pg_strcasecmp(tok, RmgrTable[rmid].rm_name) == 0 &&
-					RmgrTable[rmid].rm_mask != NULL)
+				if (RmgrIdExists(rmid) && GetRmgr(rmid).rm_mask != NULL &&
+					pg_strcasecmp(tok, GetRmgr(rmid).rm_name) == 0)
 				{
 					newwalconsistency[rmid] = true;
 					found = true;
@@ -11912,10 +11947,21 @@ check_wal_consistency_checking(char **newval, void **extra, GucSource source)
 		/* If a valid resource manager is found, check for the next one. */
 		if (!found)
 		{
-			GUC_check_errdetail("Unrecognized key word: \"%s\".", tok);
-			pfree(rawstring);
-			list_free(elemlist);
-			return false;
+			/*
+			 * Perhaps it's a custom resource manager. If so, defer checking
+			 * until InitializeWalConsistencyChecking().
+			 */
+			if (!process_shared_preload_libraries_done)
+			{
+				check_wal_consistency_checking_deferred = true;
+			}
+			else
+			{
+				GUC_check_errdetail("Unrecognized key word: \"%s\".", tok);
+				pfree(rawstring);
+				list_free(elemlist);
+				return false;
+			}
 		}
 	}
 
@@ -11931,7 +11977,20 @@ check_wal_consistency_checking(char **newval, void **extra, GucSource source)
 static void
 assign_wal_consistency_checking(const char *newval, void *extra)
 {
-	wal_consistency_checking = (bool *) extra;
+	/*
+	 * If some checks were deferred, it's possible that the checks will fail
+	 * later during InitializeWalConsistencyChecking(). But in that case, the
+	 * postmaster will exit anyway, so it's safe to proceed with the
+	 * assignment.
+	 *
+	 * Any built-in resource managers specified are assigned immediately,
+	 * which affects WAL created before shared_preload_libraries are
+	 * processed. Any custom resource managers specified won't be assigned
+	 * until after shared_preload_libraries are processed, but that's OK
+	 * because WAL for a custom resource manager can't be written before the
+	 * module is loaded anyway.
+	 */
+	wal_consistency_checking = extra;
 }
 
 static bool