Make sure we only try to free snapshots that have been passed through

alvherre · alvherre · commit 110147653aeb · 2008-07-11T02:10:14.000Z
CopySnapshot, per Neil Conway.  Also add a comment about the assumption in
GetSnapshotData that the argument is statically allocated.

Also, fix some more typos in comments in snapmgr.c.
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
@@ -23,7 +23,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.44 2008/05/12 20:02:00 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.45 2008/07/11 02:10:13 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -666,6 +666,9 @@ GetOldestXmin(bool allDbs, bool ignoreVacuum)
  *		RecentGlobalXmin: the global xmin (oldest TransactionXmin across all
  *			running transactions, except those running LAZY VACUUM).  This is
  *			the same computation done by GetOldestXmin(true, true).
+ *
+ * Note: this function should probably not be called with an argument that's
+ * not statically allocated (see xip allocation below).
  */
 Snapshot
 GetSnapshotData(Snapshot snapshot)
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
@@ -3,10 +3,9 @@
  *		PostgreSQL snapshot manager
  *
  * We keep track of snapshots in two ways: the "registered snapshots" list,
- * and the "active snapshot" stack.  All snapshots in any of them is supposed
- * to be in persistent memory.  When a snapshot is no longer in any of these
- * lists (tracked by separate refcounts of each snapshot), its memory can be
- * freed.
+ * and the "active snapshot" stack.  All snapshots in either of them live in
+ * persistent memory.  When a snapshot is no longer in any of these lists
+ * (tracked by separate refcounts on each snapshot), its memory can be freed.
  *
  * These arrangements let us reset MyProc->xmin when there are no snapshots
  * referenced by this transaction.  (One possible improvement would be to be
@@ -23,7 +22,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.3 2008/07/11 00:00:29 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.4 2008/07/11 02:10:14 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -261,6 +260,7 @@ FreeSnapshot(Snapshot snapshot)
 {
 	Assert(snapshot->regd_count == 0);
 	Assert(snapshot->active_count == 0);
+	Assert(snapshot->copied);
 
 	pfree(snapshot);
 }

Original file line number	Diff line number	Diff line change
`@@ -23,7 +23,7 @@`
`23`	`23`	`*`
`24`	`24`	`*`
`25`	`25`	`* IDENTIFICATION`
`26`		`- * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.44 2008/05/12 20:02:00 alvherre Exp $`
	`26`	`+ * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.45 2008/07/11 02:10:13 alvherre Exp $`
`27`	`27`	`*`
`28`	`28`	`*-------------------------------------------------------------------------`
`29`	`29`	`*/`
`@@ -666,6 +666,9 @@ GetOldestXmin(bool allDbs, bool ignoreVacuum)`
`666`	`666`	`* RecentGlobalXmin: the global xmin (oldest TransactionXmin across all`
`667`	`667`	`* running transactions, except those running LAZY VACUUM). This is`
`668`	`668`	`* the same computation done by GetOldestXmin(true, true).`
	`669`	`+ *`
	`670`	`+ * Note: this function should probably not be called with an argument that's`
	`671`	`+ * not statically allocated (see xip allocation below).`
`669`	`672`	`*/`
`670`	`673`	`Snapshot`
`671`	`674`	`GetSnapshotData(Snapshot snapshot)`
Original file line number	Diff line number	Diff line change
`@@ -3,10 +3,9 @@`
`3`	`3`	`* PostgreSQL snapshot manager`
`4`	`4`	`*`
`5`	`5`	`* We keep track of snapshots in two ways: the "registered snapshots" list,`
`6`		`- * and the "active snapshot" stack. All snapshots in any of them is supposed`
`7`		`- * to be in persistent memory. When a snapshot is no longer in any of these`
`8`		`- * lists (tracked by separate refcounts of each snapshot), its memory can be`
`9`		`- * freed.`
	`6`	`+ * and the "active snapshot" stack. All snapshots in either of them live in`
	`7`	`+ * persistent memory. When a snapshot is no longer in any of these lists`
	`8`	`+ * (tracked by separate refcounts on each snapshot), its memory can be freed.`
`10`	`9`	`*`
`11`	`10`	`* These arrangements let us reset MyProc->xmin when there are no snapshots`
`12`	`11`	`* referenced by this transaction. (One possible improvement would be to be`
`@@ -23,7 +22,7 @@`
`23`	`22`	`* Portions Copyright (c) 1994, Regents of the University of California`
`24`	`23`	`*`
`25`	`24`	`* IDENTIFICATION`
`26`		`- * $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.3 2008/07/11 00:00:29 neilc Exp $`
	`25`	`+ * $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.4 2008/07/11 02:10:14 alvherre Exp $`
`27`	`26`	`*`
`28`	`27`	`*-------------------------------------------------------------------------`
`29`	`28`	`*/`
`@@ -261,6 +260,7 @@ FreeSnapshot(Snapshot snapshot)`
`261`	`260`	`{`
`262`	`261`	`Assert(snapshot->regd_count == 0);`
`263`	`262`	`Assert(snapshot->active_count == 0);`
	`263`	`+ Assert(snapshot->copied);`
`264`	`264`
`265`	`265`	`pfree(snapshot);`
`266`	`266`	`}`