Show xid and xmin in pg_stat_activity and pg_stat_replication.

Christian Kruse, reviewed by Andres Freund and myself, with further
minor adjustments by me.

4 files changed, 96 insertions, 16 deletions

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index a7c6a4e094b..04dfbb0ee54 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -586,6 +586,8 @@ CREATE VIEW pg_stat_activity AS
             S.state_change,
             S.waiting,
             S.state,
+            S.backend_xid,
+            s.backend_xmin,
             S.query
     FROM pg_database D, pg_stat_get_activity(NULL) AS S, pg_authid U
     WHERE S.datid = D.oid AND
@@ -601,6 +603,7 @@ CREATE VIEW pg_stat_replication AS
             S.client_hostname,
             S.client_port,
             S.backend_start,
+            S.backend_xmin,
             W.state,
             W.sent_location,
             W.write_location,
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 305d1269124..06ea5880859 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -48,12 +48,14 @@
 #include "postmaster/autovacuum.h"
 #include "postmaster/fork_process.h"
 #include "postmaster/postmaster.h"
+#include "storage/proc.h"
 #include "storage/backendid.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"
 #include "storage/pg_shmem.h"
 #include "storage/procsignal.h"
+#include "storage/sinvaladt.h"
 #include "utils/ascii.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
@@ -213,7 +215,7 @@ typedef struct TwoPhasePgStatRecord
  */
 static MemoryContext pgStatLocalContext = NULL;
 static HTAB *pgStatDBHash = NULL;
-static PgBackendStatus *localBackendStatusTable = NULL;
+static LocalPgBackendStatus *localBackendStatusTable = NULL;
 static int	localNumBackends = 0;
 
 /*
@@ -2306,6 +2308,28 @@ pgstat_fetch_stat_beentry(int beid)
 	if (beid < 1 || beid > localNumBackends)
 		return NULL;
 
+	return &localBackendStatusTable[beid - 1].backendStatus;
+}
+
+
+/* ----------
+ * pgstat_fetch_stat_local_beentry() -
+ *
+ *  Like pgstat_fetch_stat_beentry() but with locally computed addtions (like
+ *  xid and xmin values of the backend)
+ *
+ *	NB: caller is responsible for a check if the user is permitted to see
+ *	this info (especially the querystring).
+ * ----------
+ */
+LocalPgBackendStatus *
+pgstat_fetch_stat_local_beentry(int beid)
+{
+	pgstat_read_current_status();
+
+	if (beid < 1 || beid > localNumBackends)
+		return NULL;
+
 	return &localBackendStatusTable[beid - 1];
 }
 
@@ -2783,8 +2807,8 @@ static void
 pgstat_read_current_status(void)
 {
 	volatile PgBackendStatus *beentry;
-	PgBackendStatus *localtable;
-	PgBackendStatus *localentry;
+	LocalPgBackendStatus *localtable;
+	LocalPgBackendStatus *localentry;
 	char	   *localappname,
 			   *localactivity;
 	int			i;
@@ -2795,9 +2819,9 @@ pgstat_read_current_status(void)
 
 	pgstat_setup_memcxt();
 
-	localtable = (PgBackendStatus *)
+	localtable = (LocalPgBackendStatus *)
 		MemoryContextAlloc(pgStatLocalContext,
-						   sizeof(PgBackendStatus) * MaxBackends);
+						   sizeof(LocalPgBackendStatus) * MaxBackends);
 	localappname = (char *)
 		MemoryContextAlloc(pgStatLocalContext,
 						   NAMEDATALEN * MaxBackends);
@@ -2821,19 +2845,19 @@ pgstat_read_current_status(void)
 		{
 			int			save_changecount = beentry->st_changecount;
 
-			localentry->st_procpid = beentry->st_procpid;
-			if (localentry->st_procpid > 0)
+			localentry->backendStatus.st_procpid = beentry->st_procpid;
+			if (localentry->backendStatus.st_procpid > 0)
 			{
-				memcpy(localentry, (char *) beentry, sizeof(PgBackendStatus));
+				memcpy(&localentry->backendStatus, (char *) beentry, sizeof(PgBackendStatus));
 
 				/*
 				 * strcpy is safe even if the string is modified concurrently,
 				 * because there's always a \0 at the end of the buffer.
 				 */
 				strcpy(localappname, (char *) beentry->st_appname);
-				localentry->st_appname = localappname;
+				localentry->backendStatus.st_appname = localappname;
 				strcpy(localactivity, (char *) beentry->st_activity);
-				localentry->st_activity = localactivity;
+				localentry->backendStatus.st_activity = localactivity;
 			}
 
 			if (save_changecount == beentry->st_changecount &&
@@ -2846,8 +2870,12 @@ pgstat_read_current_status(void)
 
 		beentry++;
 		/* Only valid entries get included into the local array */
-		if (localentry->st_procpid > 0)
+		if (localentry->backendStatus.st_procpid > 0)
 		{
+			BackendIdGetTransactionIds(i,
+									   &localentry->backend_xid,
+									   &localentry->backend_xmin);
+
 			localentry++;
 			localappname += NAMEDATALEN;
 			localactivity += pgstat_track_activity_query_size;
diff --git a/src/backend/storage/ipc/sinvaladt.c b/src/backend/storage/ipc/sinvaladt.c
index e7c3fb2f548..e6805d96b1c 100644
--- a/src/backend/storage/ipc/sinvaladt.c
+++ b/src/backend/storage/ipc/sinvaladt.c
@@ -25,6 +25,7 @@
 #include "storage/shmem.h"
 #include "storage/sinvaladt.h"
 #include "storage/spin.h"
+#include "access/transam.h"
 
 
 /*
@@ -401,6 +402,37 @@ BackendIdGetProc(int backendID)
 }
 
 /*
+ * BackendIdGetTransactionIds
+ *		Get the xid and xmin of the backend. The result may be out of date
+ *		arbitrarily quickly, so the caller must be careful about how this
+ *		information is used.
+ */
+void
+BackendIdGetTransactionIds(int backendID, TransactionId *xid, TransactionId *xmin)
+{
+	ProcState  *stateP;
+	SISeg	   *segP = shmInvalBuffer;
+	PGXACT	   *xact;
+
+	*xid = InvalidTransactionId;
+	*xmin = InvalidTransactionId;
+
+	/* Need to lock out additions/removals of backends */
+	LWLockAcquire(SInvalWriteLock, LW_SHARED);
+
+	if (backendID > 0 && backendID <= segP->lastBackend)
+	{
+		stateP = &segP->procState[backendID - 1];
+		xact = &ProcGlobal->allPgXact[stateP->proc->pgprocno];
+
+		*xid = xact->xid;
+		*xmin = xact->xmin;
+	}
+
+	LWLockRelease(SInvalWriteLock);
+}
+
+/*
  * SIInsertDataEntries
  *		Add new invalidation message(s) to the buffer.
  */
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index a4f31cfc7fc..140704f97ca 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -536,7 +536,7 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 
 		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
 
-		tupdesc = CreateTemplateTupleDesc(14, false);
+		tupdesc = CreateTemplateTupleDesc(16, false);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "datid",
 						   OIDOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "pid",
@@ -565,6 +565,10 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 						   TEXTOID, -1, 0);
 		TupleDescInitEntry(tupdesc, (AttrNumber) 14, "client_port",
 						   INT4OID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 15, "backend_xid",
+						   XIDOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 16, "backend_xmin",
+						   XIDOID, -1, 0);
 
 		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
 
@@ -616,9 +620,10 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 	if (funcctx->call_cntr < funcctx->max_calls)
 	{
 		/* for each row */
-		Datum		values[14];
-		bool		nulls[14];
+		Datum		values[16];
+		bool		nulls[16];
 		HeapTuple	tuple;
+		LocalPgBackendStatus *local_beentry;
 		PgBackendStatus *beentry;
 
 		MemSet(values, 0, sizeof(values));
@@ -627,12 +632,14 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		if (*(int *) (funcctx->user_fctx) > 0)
 		{
 			/* Get specific pid slot */
-			beentry = pgstat_fetch_stat_beentry(*(int *) (funcctx->user_fctx));
+			local_beentry = pgstat_fetch_stat_local_beentry(*(int *) (funcctx->user_fctx));
+			beentry = &local_beentry->backendStatus;
 		}
 		else
 		{
 			/* Get the next one in the list */
-			beentry = pgstat_fetch_stat_beentry(funcctx->call_cntr + 1);		/* 1-based index */
+			local_beentry = pgstat_fetch_stat_local_beentry(funcctx->call_cntr + 1);	/* 1-based index */
+			beentry = &local_beentry->backendStatus;
 		}
 		if (!beentry)
 		{
@@ -657,6 +664,16 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		else
 			nulls[3] = true;
 
+		if (TransactionIdIsValid(local_beentry->backend_xid))
+			values[14] = TransactionIdGetDatum(local_beentry->backend_xid);
+		else
+			nulls[14] = true;
+
+		if (TransactionIdIsValid(local_beentry->backend_xmin))
+			values[15] = TransactionIdGetDatum(local_beentry->backend_xmin);
+		else
+			nulls[15] = true;
+
 		/* Values only available to same user or superuser */
 		if (superuser() || beentry->st_userid == GetUserId())
 		{