From caa4cfa3697472a6673eb817eb34681684cba14f Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Fri, 2 Oct 2009 17:57:30 +0000 Subject: [PATCH] Ensure that a cursor has an immutable snapshot throughout its lifespan. The old coding was using a regular snapshot, referenced elsewhere, that was subject to having its command counter updated. Fix by creating a private copy of the snapshot exclusively for the cursor. Backpatch to 8.4, which is when the bug was introduced during the snapshot management rewrite. --- src/backend/commands/portalcmds.c | 13 +++++++++++-- src/backend/executor/spi.c | 7 ++----- src/backend/utils/time/snapmgr.c | 5 ++--- src/include/utils/snapmgr.h | 3 ++- src/test/regress/expected/portals.out | 15 +++++++++++++++ src/test/regress/sql/portals.sql | 12 ++++++++++++ 6 files changed, 44 insertions(+), 11 deletions(-) diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c index 1719234173..3ffdbff469 100644 --- a/src/backend/commands/portalcmds.c +++ b/src/backend/commands/portalcmds.c @@ -14,7 +14,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.79 2009/06/11 14:48:56 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.80 2009/10/02 17:57:29 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -47,6 +47,7 @@ PerformCursorOpen(PlannedStmt *stmt, ParamListInfo params, DeclareCursorStmt *cstmt = (DeclareCursorStmt *) stmt->utilityStmt; Portal portal; MemoryContext oldContext; + Snapshot snapshot; if (cstmt == NULL || !IsA(cstmt, DeclareCursorStmt)) elog(ERROR, "PerformCursorOpen called for non-cursor query"); @@ -118,10 +119,18 @@ PerformCursorOpen(PlannedStmt *stmt, ParamListInfo params, portal->cursorOptions |= CURSOR_OPT_NO_SCROLL; } + /* + * Set up snapshot for portal. Note that we need a fresh, independent copy + * of the snapshot because we don't want it to be modified by future + * CommandCounterIncrement calls. We do not register it, because + * portalmem.c will take care of that internally. + */ + snapshot = CopySnapshot(GetActiveSnapshot()); + /* * Start execution, inserting parameters if any. */ - PortalStart(portal, params, GetActiveSnapshot()); + PortalStart(portal, params, snapshot); Assert(portal->strategy == PORTAL_ONE_SELECT); diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c index 40f43ee011..8fc4536041 100644 --- a/src/backend/executor/spi.c +++ b/src/backend/executor/spi.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.208 2009/06/11 14:48:57 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.209 2009/10/02 17:57:30 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -1211,10 +1211,7 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan, } } - /* - * Set up the snapshot to use. (PortalStart will do PushActiveSnapshot, - * so we skip that here.) - */ + /* Set up the snapshot to use. */ if (read_only) snapshot = GetActiveSnapshot(); else diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index 73d597d7b3..f8531276a4 100644 --- a/src/backend/utils/time/snapmgr.c +++ b/src/backend/utils/time/snapmgr.c @@ -19,7 +19,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.10 2009/06/11 14:49:06 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.11 2009/10/02 17:57:30 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -104,7 +104,6 @@ bool FirstSnapshotSet = false; static bool registered_serializable = false; -static Snapshot CopySnapshot(Snapshot snapshot); static void FreeSnapshot(Snapshot snapshot); static void SnapshotResetXmin(void); @@ -192,7 +191,7 @@ SnapshotSetCommandId(CommandId curcid) * The copy is palloc'd in TopTransactionContext and has initial refcounts set * to 0. The returned snapshot has the copied flag set. */ -static Snapshot +Snapshot CopySnapshot(Snapshot snapshot) { Snapshot newsnap; diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h index 979a52c622..a82e53bb17 100644 --- a/src/include/utils/snapmgr.h +++ b/src/include/utils/snapmgr.h @@ -6,7 +6,7 @@ * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/utils/snapmgr.h,v 1.5 2009/06/11 14:49:13 momjian Exp $ + * $PostgreSQL: pgsql/src/include/utils/snapmgr.h,v 1.6 2009/10/02 17:57:30 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -26,6 +26,7 @@ extern TransactionId RecentGlobalXmin; extern Snapshot GetTransactionSnapshot(void); extern Snapshot GetLatestSnapshot(void); extern void SnapshotSetCommandId(CommandId curcid); +extern Snapshot CopySnapshot(Snapshot snapshot); extern void PushActiveSnapshot(Snapshot snapshot); extern void PushUpdatedSnapshot(Snapshot snapshot); diff --git a/src/test/regress/expected/portals.out b/src/test/regress/expected/portals.out index 95dcea5a1d..be7348d6b2 100644 --- a/src/test/regress/expected/portals.out +++ b/src/test/regress/expected/portals.out @@ -1242,3 +1242,18 @@ FETCH FROM c1; DELETE FROM ucview WHERE CURRENT OF c1; -- fail, views not supported ERROR: WHERE CURRENT OF on a view is not implemented ROLLBACK; +-- Make sure snapshot management works okay, per bug report in +-- 235395b90909301035v7228ce63q392931f15aa74b31@mail.gmail.com +BEGIN; +SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; +CREATE TABLE cursor (a int); +INSERT INTO cursor VALUES (1); +DECLARE c1 NO SCROLL CURSOR FOR SELECT * FROM cursor FOR UPDATE; +UPDATE cursor SET a = 2; +FETCH ALL FROM c1; + a +--- +(0 rows) + +COMMIT; +DROP TABLE cursor; diff --git a/src/test/regress/sql/portals.sql b/src/test/regress/sql/portals.sql index 4265aaa43c..585a7c25ea 100644 --- a/src/test/regress/sql/portals.sql +++ b/src/test/regress/sql/portals.sql @@ -458,3 +458,15 @@ DECLARE c1 CURSOR FOR SELECT * FROM ucview; FETCH FROM c1; DELETE FROM ucview WHERE CURRENT OF c1; -- fail, views not supported ROLLBACK; + +-- Make sure snapshot management works okay, per bug report in +-- 235395b90909301035v7228ce63q392931f15aa74b31@mail.gmail.com +BEGIN; +SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; +CREATE TABLE cursor (a int); +INSERT INTO cursor VALUES (1); +DECLARE c1 NO SCROLL CURSOR FOR SELECT * FROM cursor FOR UPDATE; +UPDATE cursor SET a = 2; +FETCH ALL FROM c1; +COMMIT; +DROP TABLE cursor;