Make pg_waldump report more detail information about PREPARE TRANSACTION record.

This commit changes xact_desc() so that it reports the detail information about
PREPARE TRANSACTION record, like GID (global transaction identifier),
timestamp at prepare transaction, delete-on-abort/commit relations,
XID of subtransactions, and invalidation messages. These are helpful
when diagnosing 2PC-related troubles.

Author: Fujii Masao
Reviewed-by: Michael Paquier, Andrey Lepikhov, Kyotaro Horiguchi, Julien Rouhaud, Alvaro Herrera
Discussion: https://postgr.es/m/CAHGQGwEvhASad4JJnCv=0dW2TJypZgW_Vpb-oZik2a3utCqcrA@mail.gmail.com

src/backend/access/rmgrdesc/standbydesc.c

@@ -102,6 +102,10 @@ standby_desc_invalidations(StringInfo buf,
 {
 	int			i;
 
+	/* Do nothing if there are no invalidation messages */
+	if (nmsgs <= 0)
+		return;
+
 	if (relcacheInitFileInval)
 		appendStringInfo(buf, "; relcache init file inval dbid %u tsid %u",
 						 dbId, tsId);

src/backend/access/rmgrdesc/xactdesc.c

@@ -209,43 +209,95 @@ ParseAbortRecord(uint8 info, xl_xact_abort *xlrec, xl_xact_parsed_abort *parsed)
 	}
 }
 
-static void
-xact_desc_commit(StringInfo buf, uint8 info, xl_xact_commit *xlrec, RepOriginId origin_id)
+/*
+ * ParsePrepareRecord
+ */
+void
+ParsePrepareRecord(uint8 info, xl_xact_prepare *xlrec, xl_xact_parsed_prepare *parsed)
 {
-	xl_xact_parsed_commit parsed;
-	int			i;
+	char	   *bufptr;
 
-	ParseCommitRecord(info, xlrec, &parsed);
+	bufptr = ((char *) xlrec) + MAXALIGN(sizeof(xl_xact_prepare));
 
-	/* If this is a prepared xact, show the xid of the original xact */
-	if (TransactionIdIsValid(parsed.twophase_xid))
-		appendStringInfo(buf, "%u: ", parsed.twophase_xid);
+	memset(parsed, 0, sizeof(*parsed));
 
-	appendStringInfoString(buf, timestamptz_to_str(xlrec->xact_time));
+	parsed->xact_time = xlrec->prepared_at;
+	parsed->origin_lsn = xlrec->origin_lsn;
+	parsed->origin_timestamp = xlrec->origin_timestamp;
+	parsed->twophase_xid = xlrec->xid;
+	parsed->dbId = xlrec->database;
+	parsed->nsubxacts = xlrec->nsubxacts;
+	parsed->nrels = xlrec->ncommitrels;
+	parsed->nabortrels = xlrec->nabortrels;
+	parsed->nmsgs = xlrec->ninvalmsgs;
+
+	strncpy(parsed->twophase_gid, bufptr, xlrec->gidlen);
+	bufptr += MAXALIGN(xlrec->gidlen);
 
-	if (parsed.nrels > 0)
+	parsed->subxacts = (TransactionId *) bufptr;
+	bufptr += MAXALIGN(xlrec->nsubxacts * sizeof(TransactionId));
+
+	parsed->xnodes = (RelFileNode *) bufptr;
+	bufptr += MAXALIGN(xlrec->ncommitrels * sizeof(RelFileNode));
+
+	parsed->abortnodes = (RelFileNode *) bufptr;
+	bufptr += MAXALIGN(xlrec->nabortrels * sizeof(RelFileNode));
+
+	parsed->msgs = (SharedInvalidationMessage *) bufptr;
+	bufptr += MAXALIGN(xlrec->ninvalmsgs * sizeof(SharedInvalidationMessage));
+}
+
+static void
+xact_desc_relations(StringInfo buf, char *label, int nrels,
+					RelFileNode *xnodes)
+{
+	int		i;
+
+	if (nrels > 0)
 	{
-		appendStringInfoString(buf, "; rels:");
-		for (i = 0; i < parsed.nrels; i++)
+		appendStringInfo(buf, "; %s:", label);
+		for (i = 0; i < nrels; i++)
 		{
-			char	   *path = relpathperm(parsed.xnodes[i], MAIN_FORKNUM);
+			char	   *path = relpathperm(xnodes[i], MAIN_FORKNUM);
 
 			appendStringInfo(buf, " %s", path);
 			pfree(path);
 		}
 	}
-	if (parsed.nsubxacts > 0)
+}
+
+static void
+xact_desc_subxacts(StringInfo buf, int nsubxacts, TransactionId *subxacts)
+{
+	int		i;
+
+	if (nsubxacts > 0)
 	{
 		appendStringInfoString(buf, "; subxacts:");
-		for (i = 0; i < parsed.nsubxacts; i++)
-			appendStringInfo(buf, " %u", parsed.subxacts[i]);
+		for (i = 0; i < nsubxacts; i++)
+			appendStringInfo(buf, " %u", subxacts[i]);
 	}
-	if (parsed.nmsgs > 0)
-	{
+}
+
+static void
+xact_desc_commit(StringInfo buf, uint8 info, xl_xact_commit *xlrec, RepOriginId origin_id)
+{
+	xl_xact_parsed_commit parsed;
+
+	ParseCommitRecord(info, xlrec, &parsed);
+
+	/* If this is a prepared xact, show the xid of the original xact */
+	if (TransactionIdIsValid(parsed.twophase_xid))
+		appendStringInfo(buf, "%u: ", parsed.twophase_xid);
+
+	appendStringInfoString(buf, timestamptz_to_str(xlrec->xact_time));
+
+	xact_desc_relations(buf, "rels", parsed.nrels, parsed.xnodes);
+	xact_desc_subxacts(buf, parsed.nsubxacts, parsed.subxacts);
+
 	standby_desc_invalidations(
 						buf, parsed.nmsgs, parsed.msgs, parsed.dbId, parsed.tsId,
 						XactCompletionRelcacheInitFileInval(parsed.xinfo));
-	}
 
 	if (XactCompletionForceSyncCommit(parsed.xinfo))
 		appendStringInfoString(buf, "; sync");
@@ -264,7 +316,6 @@ static void
 xact_desc_abort(StringInfo buf, uint8 info, xl_xact_abort *xlrec)
 {
 	xl_xact_parsed_abort parsed;
-	int			i;
 
 	ParseAbortRecord(info, xlrec, &parsed);
 
@@ -273,24 +324,29 @@ xact_desc_abort(StringInfo buf, uint8 info, xl_xact_abort *xlrec)
 		appendStringInfo(buf, "%u: ", parsed.twophase_xid);
 
 	appendStringInfoString(buf, timestamptz_to_str(xlrec->xact_time));
-	if (parsed.nrels > 0)
-	{
-		appendStringInfoString(buf, "; rels:");
-		for (i = 0; i < parsed.nrels; i++)
-		{
-			char	   *path = relpathperm(parsed.xnodes[i], MAIN_FORKNUM);
 
-			appendStringInfo(buf, " %s", path);
-			pfree(path);
-		}
-	}
+	xact_desc_relations(buf, "rels", parsed.nrels, parsed.xnodes);
+	xact_desc_subxacts(buf, parsed.nsubxacts, parsed.subxacts);
+}
 
-	if (parsed.nsubxacts > 0)
-	{
-		appendStringInfoString(buf, "; subxacts:");
-		for (i = 0; i < parsed.nsubxacts; i++)
-			appendStringInfo(buf, " %u", parsed.subxacts[i]);
-	}
+static void
+xact_desc_prepare(StringInfo buf, uint8 info, xl_xact_prepare *xlrec)
+{
+	xl_xact_parsed_prepare parsed;
+
+	ParsePrepareRecord(info, xlrec, &parsed);
+
+	appendStringInfo(buf, "gid %s: ", parsed.twophase_gid);
+	appendStringInfoString(buf, timestamptz_to_str(parsed.xact_time));
+
+	xact_desc_relations(buf, "rels(commit)", parsed.nrels, parsed.xnodes);
+	xact_desc_relations(buf, "rels(abort)", parsed.nabortrels,
+						parsed.abortnodes);
+	xact_desc_subxacts(buf, parsed.nsubxacts, parsed.subxacts);
+
+	standby_desc_invalidations(
+						buf, parsed.nmsgs, parsed.msgs, parsed.dbId, parsed.tsId,
+						xlrec->initfileinval);
 }
 
 static void
@@ -323,6 +379,12 @@ xact_desc(StringInfo buf, XLogReaderState *record)
 
 		xact_desc_abort(buf, XLogRecGetInfo(record), xlrec);
 	}
+	else if (info == XLOG_XACT_PREPARE)
+	{
+		xl_xact_prepare *xlrec = (xl_xact_prepare *) rec;
+
+		xact_desc_prepare(buf, XLogRecGetInfo(record), xlrec);
+	}
 	else if (info == XLOG_XACT_ASSIGNMENT)
 	{
 		xl_xact_assignment *xlrec = (xl_xact_assignment *) rec;

src/backend/access/transam/twophase.c

@@ -910,23 +910,7 @@ TwoPhaseGetDummyProc(TransactionId xid, bool lock_held)
  */
 #define TWOPHASE_MAGIC	0x57F94534	/* format identifier */
 
-typedef struct TwoPhaseFileHeader
-{
-	uint32		magic;			/* format identifier */
-	uint32		total_len;		/* actual file length */
-	TransactionId xid;			/* original transaction XID */
-	Oid			database;		/* OID of database it was in */
-	TimestampTz prepared_at;	/* time of preparation */
-	Oid			owner;			/* user running the transaction */
-	int32		nsubxacts;		/* number of following subxact XIDs */
-	int32		ncommitrels;	/* number of delete-on-commit rels */
-	int32		nabortrels;		/* number of delete-on-abort rels */
-	int32		ninvalmsgs;		/* number of cache invalidation messages */
-	bool		initfileinval;	/* does relcache init file need invalidation? */
-	uint16		gidlen;			/* length of the GID - GID follows the header */
-	XLogRecPtr	origin_lsn;		/* lsn of this record at origin node */
-	TimestampTz origin_timestamp;	/* time of prepare at origin node */
-} TwoPhaseFileHeader;
+typedef xl_xact_prepare TwoPhaseFileHeader;
 
 /*
  * Header for each record in a state file
@@ -1331,44 +1315,6 @@ ReadTwoPhaseFile(TransactionId xid, bool missing_ok)
 	return buf;
 }
 
-/*
- * ParsePrepareRecord
- */
-void
-ParsePrepareRecord(uint8 info, char *xlrec, xl_xact_parsed_prepare *parsed)
-{
-	TwoPhaseFileHeader *hdr;
-	char	   *bufptr;
-
-	hdr = (TwoPhaseFileHeader *) xlrec;
-	bufptr = xlrec + MAXALIGN(sizeof(TwoPhaseFileHeader));
-
-	parsed->origin_lsn = hdr->origin_lsn;
-	parsed->origin_timestamp = hdr->origin_timestamp;
-	parsed->twophase_xid = hdr->xid;
-	parsed->dbId = hdr->database;
-	parsed->nsubxacts = hdr->nsubxacts;
-	parsed->nrels = hdr->ncommitrels;
-	parsed->nabortrels = hdr->nabortrels;
-	parsed->nmsgs = hdr->ninvalmsgs;
-
-	strncpy(parsed->twophase_gid, bufptr, hdr->gidlen);
-	bufptr += MAXALIGN(hdr->gidlen);
-
-	parsed->subxacts = (TransactionId *) bufptr;
-	bufptr += MAXALIGN(hdr->nsubxacts * sizeof(TransactionId));
-
-	parsed->xnodes = (RelFileNode *) bufptr;
-	bufptr += MAXALIGN(hdr->ncommitrels * sizeof(RelFileNode));
-
-	parsed->abortnodes = (RelFileNode *) bufptr;
-	bufptr += MAXALIGN(hdr->nabortrels * sizeof(RelFileNode));
-
-	parsed->msgs = (SharedInvalidationMessage *) bufptr;
-	bufptr += MAXALIGN(hdr->ninvalmsgs * sizeof(SharedInvalidationMessage));
-}
-
-
 
 /*
  * Reads 2PC data from xlog. During checkpoint this data will be moved to

src/include/access/twophase.h

@@ -47,8 +47,6 @@ extern bool StandbyTransactionIdIsPrepared(TransactionId xid);
 
 extern TransactionId PrescanPreparedTransactions(TransactionId **xids_p,
 												 int *nxids_p);
-extern void ParsePrepareRecord(uint8 info, char *xlrec,
-							   xl_xact_parsed_prepare *parsed);
 extern void StandbyRecoverPreparedTransactions(void);
 extern void RecoverPreparedTransactions(void);
 

src/include/access/xact.h

@@ -292,6 +292,24 @@ typedef struct xl_xact_abort
 } xl_xact_abort;
 #define MinSizeOfXactAbort sizeof(xl_xact_abort)
 
+typedef struct xl_xact_prepare
+{
+	uint32		magic;			/* format identifier */
+	uint32		total_len;		/* actual file length */
+	TransactionId xid;			/* original transaction XID */
+	Oid			database;		/* OID of database it was in */
+	TimestampTz prepared_at;	/* time of preparation */
+	Oid			owner;			/* user running the transaction */
+	int32		nsubxacts;		/* number of following subxact XIDs */
+	int32		ncommitrels;	/* number of delete-on-commit rels */
+	int32		nabortrels;		/* number of delete-on-abort rels */
+	int32		ninvalmsgs;		/* number of cache invalidation messages */
+	bool		initfileinval;	/* does relcache init file need invalidation? */
+	uint16		gidlen;			/* length of the GID - GID follows the header */
+	XLogRecPtr	origin_lsn;		/* lsn of this record at origin node */
+	TimestampTz origin_timestamp;	/* time of prepare at origin node */
+} xl_xact_prepare;
+
 /*
  * Commit/Abort records in the above form are a bit verbose to parse, so
  * there's a deconstructed versions generated by ParseCommit/AbortRecord() for
@@ -435,6 +453,7 @@ extern const char *xact_identify(uint8 info);
 /* also in xactdesc.c, so they can be shared between front/backend code */
 extern void ParseCommitRecord(uint8 info, xl_xact_commit *xlrec, xl_xact_parsed_commit *parsed);
 extern void ParseAbortRecord(uint8 info, xl_xact_abort *xlrec, xl_xact_parsed_abort *parsed);
+extern void ParsePrepareRecord(uint8 info, xl_xact_prepare *xlrec, xl_xact_parsed_prepare *parsed);
 
 extern void EnterParallelMode(void);
 extern void ExitParallelMode(void);