Add a time-of-preparation column to the pg_prepared_xacts view, per an

old suggestion by Oliver Jowett.  Also, add a transaction column to the
pg_locks view to show the xid of each transaction holding or awaiting
locks; this allows prepared transactions to be properly associated with
the locks they own.  There was already a column named 'transaction',
and I chose to rename it to 'transactionid' --- since this column is
new in the current devel cycle there should be no backwards compatibility
issue to worry about.

Author: tglsfdc

doc/src/sgml/catalogs.sgml

@@ -1,6 +1,6 @@
 <!--
  Documentation of the system catalogs, directed toward PostgreSQL developers
- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.104 2005/06/17 22:32:41 tgl Exp $
+ $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.105 2005/06/18 19:33:41 tgl Exp $
  -->
 
 <chapter id="catalogs">
@@ -4090,7 +4090,7 @@
        <literal>extend</>,
        <literal>page</>,
        <literal>tuple</>,
-       <literal>transaction</>,
+       <literal>transactionid</>,
        <literal>object</>, or
        <literal>userlock</>
       </entry>
@@ -4132,7 +4132,7 @@
       </entry>
      </row>
      <row>
-      <entry><structfield>transaction</structfield></entry>
+      <entry><structfield>transactionid</structfield></entry>
       <entry><type>xid</type></entry>
       <entry></entry>
       <entry>
@@ -4168,13 +4168,21 @@
        zero.  NULL if the object is not a general database object
       </entry>
      </row>
+     <row>
+      <entry><structfield>transaction</structfield></entry>
+      <entry><type>xid</type></entry>
+      <entry></entry>
+      <entry>
+       ID of the transaction that is holding or awaiting this lock.
+      </entry>
+     </row>
      <row>
       <entry><structfield>pid</structfield></entry>
       <entry><type>integer</type></entry>
       <entry></entry>
       <entry>
        Process ID of the server process holding or awaiting this
-       lock.  Zero if the lock is held by a prepared transaction.
+       lock.  Null if the lock is held by a prepared transaction.
       </entry>
      </row>
      <row>
@@ -4196,12 +4204,12 @@
 
   <para>
    <structfield>granted</structfield> is true in a row representing a lock
-   held by the indicated session.  False indicates that this session is
+   held by the indicated transaction.  False indicates that this transaction is
    currently waiting to acquire this lock, which implies that some other
-   session is holding a conflicting lock mode on the same lockable object.
-   The waiting session will sleep until the other lock is released (or a
-   deadlock situation is detected). A single session can be waiting to acquire
-   at most one lock at a time.
+   transaction is holding a conflicting lock mode on the same lockable object.
+   The waiting transaction will sleep until the other lock is released (or a
+   deadlock situation is detected). A single transaction can be waiting to
+   acquire at most one lock at a time.
   </para>
 
   <para>
@@ -4253,6 +4261,13 @@
    <structfield>procpid</structfield> column of the
    <structname>pg_stat_activity</structname> view to get more
    information on the session holding or waiting to hold the lock.
+   Also, if you are using prepared transactions, the
+   <structfield>transaction</> column can be joined to the
+   <structfield>transaction</structfield> column of the
+   <structname>pg_prepared_xacts</structname> view to get more
+   information on prepared transactions that hold locks.
+   (A prepared transaction can never be waiting for a lock,
+   but it continues to hold the locks it acquired while running.)
   </para>
 
  </sect1>
@@ -4306,6 +4321,14 @@
        Global transaction identifier that was assigned to the transaction
       </entry>
      </row>
+     <row>
+      <entry><structfield>prepared</structfield></entry>
+      <entry><type>timestamp with time zone</type></entry>
+      <entry></entry>
+      <entry>
+       Time at which the transaction was prepared for commit
+      </entry>
+     </row>
      <row>
       <entry><structfield>owner</structfield></entry>
       <entry><type>name</type></entry>

src/backend/access/transam/twophase.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *		$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.2 2005/06/18 05:21:09 tgl Exp $
+ *		$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.3 2005/06/18 19:33:41 tgl Exp $
  *
  * NOTES
  *		Each global transaction is associated with a global transaction
@@ -104,6 +104,7 @@ int max_prepared_xacts = 50;
 typedef struct GlobalTransactionData
 {
 	PGPROC		proc;			/* dummy proc */
+	TimestampTz	prepared_at;	/* time of preparation */
 	AclId		owner;			/* ID of user that executed the xact */
 	TransactionId locking_xid;	/* top-level XID of backend working on xact */
 	bool		valid;			/* TRUE if fully prepared */
@@ -202,7 +203,8 @@ TwoPhaseShmemInit(void)
  * assuming that we can use very much backend context.
  */
 GlobalTransaction
-MarkAsPreparing(TransactionId xid, Oid databaseid, char *gid, AclId owner)
+MarkAsPreparing(TransactionId xid, const char *gid,
+				TimestampTz prepared_at, AclId owner, Oid databaseid)
 {
 	GlobalTransaction	gxact;
 	int i;
@@ -278,6 +280,7 @@ MarkAsPreparing(TransactionId xid, Oid databaseid, char *gid, AclId owner)
 	gxact->proc.subxids.overflowed = false;
 	gxact->proc.subxids.nxids = 0;
 
+	gxact->prepared_at = prepared_at;
 	gxact->owner = owner;
 	gxact->locking_xid = xid;
 	gxact->valid = false;
@@ -342,7 +345,7 @@ MarkAsPrepared(GlobalTransaction gxact)
  *		Locate the prepared transaction and mark it busy for COMMIT or PREPARE.
  */
 static GlobalTransaction
-LockGXact(char *gid, AclId user)
+LockGXact(const char *gid, AclId user)
 {
 	int i;
 
@@ -509,14 +512,16 @@ pg_prepared_xact(PG_FUNCTION_ARGS)
 
 		/* build tupdesc for result tuples */
 		/* this had better match pg_prepared_xacts view in system_views.sql */
-		tupdesc = CreateTemplateTupleDesc(4, false);
+		tupdesc = CreateTemplateTupleDesc(5, false);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "transaction",
 						   XIDOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "gid",
 						   TEXTOID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "ownerid",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepared",
+						   TIMESTAMPTZOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "ownerid",
 						   INT4OID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "dbid",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "dbid",
 						   OIDOID, -1, 0);
 
 		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
@@ -540,8 +545,8 @@ pg_prepared_xact(PG_FUNCTION_ARGS)
 	while (status->array != NULL && status->currIdx < status->ngxacts)
 	{
 		GlobalTransaction gxact = &status->array[status->currIdx++];
-		Datum		values[4];
-		bool		nulls[4];
+		Datum		values[5];
+		bool		nulls[5];
 		HeapTuple	tuple;
 		Datum		result;
 
@@ -556,8 +561,9 @@ pg_prepared_xact(PG_FUNCTION_ARGS)
 
 		values[0] = TransactionIdGetDatum(gxact->proc.xid);
 		values[1] = DirectFunctionCall1(textin, CStringGetDatum(gxact->gid));
-		values[2] = Int32GetDatum(gxact->owner);
-		values[3] = ObjectIdGetDatum(gxact->proc.databaseId);
+		values[2] = TimestampTzGetDatum(gxact->prepared_at);
+		values[3] = Int32GetDatum(gxact->owner);
+		values[4] = ObjectIdGetDatum(gxact->proc.databaseId);
 
 		tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
 		result = HeapTupleGetDatum(tuple);
@@ -636,14 +642,15 @@ TwoPhaseGetDummyProc(TransactionId xid)
 /*
  * Header for a 2PC state file
  */
-#define TWOPHASE_MAGIC	0x57F94530		/* format identifier */
+#define TWOPHASE_MAGIC	0x57F94531		/* 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 */
 	AclId			owner;				/* user running the transaction */
 	int32			nsubxacts;			/* number of following subxact XIDs */
 	int32			ncommitrels;		/* number of delete-on-commit rels */
@@ -741,8 +748,9 @@ StartPrepare(GlobalTransaction gxact)
 	hdr.magic = TWOPHASE_MAGIC;
 	hdr.total_len = 0;			/* EndPrepare will fill this in */
 	hdr.xid = xid;
-	hdr.database = MyDatabaseId;
-	hdr.owner = GetUserId();
+	hdr.database = gxact->proc.databaseId;
+	hdr.prepared_at = gxact->prepared_at;
+	hdr.owner = gxact->owner;
 	hdr.nsubxacts = xactGetCommittedChildren(&children);
 	hdr.ncommitrels = smgrGetPendingDeletes(true, &commitrels);
 	hdr.nabortrels = smgrGetPendingDeletes(false, &abortrels);
@@ -1046,7 +1054,7 @@ ReadTwoPhaseFile(TransactionId xid)
  * FinishPreparedTransaction: execute COMMIT PREPARED or ROLLBACK PREPARED
  */
 void
-FinishPreparedTransaction(char *gid, bool isCommit)
+FinishPreparedTransaction(const char *gid, bool isCommit)
 {
 	GlobalTransaction gxact;
 	TransactionId xid;
@@ -1474,15 +1482,20 @@ RecoverPreparedTransactions(void)
 
 			/*
 			 * Reconstruct subtrans state for the transaction --- needed
-			 * because pg_subtrans is not preserved over a restart
+			 * because pg_subtrans is not preserved over a restart.  Note
+			 * that we are linking all the subtransactions directly to the
+			 * top-level XID; there may originally have been a more complex
+			 * hierarchy, but there's no need to restore that exactly.
 			 */
 			for (i = 0; i < hdr->nsubxacts; i++)
 				SubTransSetParent(subxids[i], xid);
 
 			/*
 			 * Recreate its GXACT and dummy PGPROC
 			 */
-			gxact = MarkAsPreparing(xid, hdr->database, hdr->gid, hdr->owner);
+			gxact = MarkAsPreparing(xid, hdr->gid,
+									hdr->prepared_at,
+									hdr->owner, hdr->database);
 			GXactLoadSubxactData(gxact, hdr->nsubxacts, subxids);
 			MarkAsPrepared(gxact);
 

src/backend/access/transam/xact.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.205 2005/06/17 22:32:42 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.206 2005/06/18 19:33:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1630,6 +1630,9 @@ PrepareTransaction(void)
 	TransactionState	s = CurrentTransactionState;
 	TransactionId		xid = GetCurrentTransactionId();
 	GlobalTransaction	gxact;
+	TimestampTz			prepared_at;
+	AbsoluteTime		PreparedSec;	/* integer part */
+	int			PreparedUSec;	/* microsecond part */
 
 	ShowTransactionState("PrepareTransaction");
 
@@ -1692,14 +1695,18 @@ PrepareTransaction(void)
 	 */
 	s->state = TRANS_PREPARE;
 
+	PreparedSec = GetCurrentAbsoluteTimeUsec(&PreparedUSec);
+	prepared_at = AbsoluteTimeUsecToTimestampTz(PreparedSec, PreparedUSec);
+
 	/* Tell bufmgr and smgr to prepare for commit */
 	BufmgrCommit();
 
 	/*
 	 * Reserve the GID for this transaction. This could fail if the
 	 * requested GID is invalid or already in use.
 	 */
-	gxact = MarkAsPreparing(xid, MyDatabaseId, prepareGID, GetUserId());
+	gxact = MarkAsPreparing(xid, prepareGID, prepared_at,
+							GetUserId(), MyDatabaseId);
 	prepareGID = NULL;
 
 	/*

src/backend/catalog/system_views.sql

@@ -3,7 +3,7 @@
  *
  * Copyright (c) 1996-2005, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/backend/catalog/system_views.sql,v 1.14 2005/06/17 22:32:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/catalog/system_views.sql,v 1.15 2005/06/18 19:33:42 tgl Exp $
  */
 
 CREATE VIEW pg_user AS 
@@ -106,15 +106,16 @@ CREATE VIEW pg_locks AS
     SELECT * 
     FROM pg_lock_status() AS L
     (locktype text, database oid, relation oid, page int4, tuple int2,
-     transaction xid, classid oid, objid oid, objsubid int2,
-     pid int4, mode text, granted boolean);
+     transactionid xid, classid oid, objid oid, objsubid int2,
+     transaction xid, pid int4, mode text, granted boolean);
 
 CREATE VIEW pg_prepared_xacts AS
-    SELECT P.transaction, P.gid, U.usename AS owner, D.datname AS database
+    SELECT P.transaction, P.gid, P.prepared,
+           U.usename AS owner, D.datname AS database
     FROM pg_prepared_xact() AS P
-    (transaction xid, gid text, ownerid int4, dbid oid)
-         LEFT JOIN pg_database D ON P.dbid = D.oid
-         LEFT JOIN pg_shadow U ON P.ownerid = U.usesysid;
+    (transaction xid, gid text, prepared timestamptz, ownerid int4, dbid oid)
+         LEFT JOIN pg_shadow U ON P.ownerid = U.usesysid
+         LEFT JOIN pg_database D ON P.dbid = D.oid;
 
 CREATE VIEW pg_settings AS 
     SELECT * 

src/backend/utils/adt/lockfuncs.c

@@ -6,7 +6,7 @@
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *		$PostgreSQL: pgsql/src/backend/utils/adt/lockfuncs.c,v 1.18 2005/05/17 21:46:10 tgl Exp $
+ *		$PostgreSQL: pgsql/src/backend/utils/adt/lockfuncs.c,v 1.19 2005/06/18 19:33:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -26,7 +26,7 @@ static const char * const LockTagTypeNames[] = {
 	"extend",
 	"page",
 	"tuple",
-	"transaction",
+	"transactionid",
 	"object",
 	"userlock"
 };
@@ -64,7 +64,7 @@ pg_lock_status(PG_FUNCTION_ARGS)
 
 		/* build tupdesc for result tuples */
 		/* this had better match pg_locks view in system_views.sql */
-		tupdesc = CreateTemplateTupleDesc(12, false);
+		tupdesc = CreateTemplateTupleDesc(13, false);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "locktype",
 						   TEXTOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "database",
@@ -75,19 +75,21 @@ pg_lock_status(PG_FUNCTION_ARGS)
 						   INT4OID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "tuple",
 						   INT2OID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 6, "transaction",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 6, "transactionid",
 						   XIDOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 7, "classid",
 						   OIDOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 8, "objid",
 						   OIDOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 9, "objsubid",
 						   INT2OID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 10, "pid",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 10, "transaction",
+						   XIDOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 11, "pid",
 						   INT4OID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 11, "mode",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 12, "mode",
 						   TEXTOID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 12, "granted",
+		TupleDescInitEntry(tupdesc, (AttrNumber) 13, "granted",
 						   BOOLOID, -1, 0);
 
 		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
@@ -118,8 +120,8 @@ pg_lock_status(PG_FUNCTION_ARGS)
 		LOCKMODE	mode = 0;
 		const char *locktypename;
 		char		tnbuf[32];
-		Datum		values[12];
-		char		nulls[12];
+		Datum		values[13];
+		char		nulls[13];
 		HeapTuple	tuple;
 		Datum		result;
 
@@ -249,10 +251,14 @@ pg_lock_status(PG_FUNCTION_ARGS)
 				break;
 		}
 
-		values[9] = Int32GetDatum(proc->pid);
-		values[10] = DirectFunctionCall1(textin,
+		values[9] = TransactionIdGetDatum(proc->xid);
+		if (proc->pid != 0)
+			values[10] = Int32GetDatum(proc->pid);
+		else
+			nulls[10] = 'n';
+		values[11] = DirectFunctionCall1(textin,
 										 CStringGetDatum(GetLockmodeName(mode)));
-		values[11] = BoolGetDatum(granted);
+		values[12] = BoolGetDatum(granted);
 
 		tuple = heap_formtuple(funcctx->tuple_desc, values, nulls);
 		result = HeapTupleGetDatum(tuple);