From 07cefdfb7a1c1a7ae96783c9723102250a4c3bad Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Wed, 7 Oct 2009 16:27:18 +0000 Subject: [PATCH] Fix snapshot management, take two. Partially revert the previous patch I installed and replace it with a more general fix: any time a snapshot is pushed as Active, we need to ensure that it will not be modified in the future. This means that if the same snapshot is used as CurrentSnapshot, it needs to be copied separately. This affects serializable transactions only, because CurrentSnapshot has already been copied by RegisterSnapshot and so PushActiveSnapshot does not think it needs another copy. However, CommandCounterIncrement would modify CurrentSnapshot, whereas ActiveSnapshots must not have their command counters incremented. I say "partially" because the regression test I added for the previous bug has been kept. (This restores 8.3 behavior, because before snapmgr.c existed, any snapshot set as Active was copied.) Per bug report from Stuart Bishop in 6bc73d4c0910042358k3d1adff3qa36f8df75198ecea@mail.gmail.com --- src/backend/commands/portalcmds.c | 13 ++--------- src/backend/utils/time/snapmgr.c | 22 +++++++++++++----- src/include/utils/snapmgr.h | 3 +-- src/test/regress/expected/triggers.out | 31 ++++++++++++++++++++++++++ src/test/regress/sql/triggers.sql | 30 +++++++++++++++++++++++++ 5 files changed, 80 insertions(+), 19 deletions(-) diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c index 3ffdbff469..0644ffc72b 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 1.80 2009/10/02 17:57:29 alvherre Exp $ + * $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.81 2009/10/07 16:27:18 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -47,7 +47,6 @@ 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"); @@ -119,18 +118,10 @@ 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, snapshot); + PortalStart(portal, params, GetActiveSnapshot()); Assert(portal->strategy == PORTAL_ONE_SELECT); diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c index f8531276a4..41ff3405a3 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 1.11 2009/10/02 17:57:30 alvherre Exp $ + * $PostgreSQL: pgsql/src/backend/utils/time/snapmgr.c,v 1.12 2009/10/07 16:27:18 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -104,6 +104,7 @@ bool FirstSnapshotSet = false; static bool registered_serializable = false; +static Snapshot CopySnapshot(Snapshot snapshot); static void FreeSnapshot(Snapshot snapshot); static void SnapshotResetXmin(void); @@ -191,7 +192,7 @@ 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. */ -Snapshot +static Snapshot CopySnapshot(Snapshot snapshot) { Snapshot newsnap; @@ -254,8 +255,9 @@ FreeSnapshot(Snapshot snapshot) * PushActiveSnapshot * Set the given snapshot as the current active snapshot * - * If this is the first use of this snapshot, create a new long-lived copy with - * active refcount=1. Otherwise, only increment the refcount. + * If the passed snapshot is a statically-allocated one, or it is possibly + * subject to a future command counter update, create a new long-lived copy + * with active refcount=1. Otherwise, only increment the refcount. */ void PushActiveSnapshot(Snapshot snap) @@ -265,8 +267,16 @@ PushActiveSnapshot(Snapshot snap) Assert(snap != InvalidSnapshot); newactive = MemoryContextAlloc(TopTransactionContext, sizeof(ActiveSnapshotElt)); - /* Static snapshot? Create a persistent copy */ - newactive->as_snap = snap->copied ? snap : CopySnapshot(snap); + + /* + * Checking SecondarySnapshot is probably useless here, but it seems better + * to be sure. + */ + if (snap == CurrentSnapshot || snap == SecondarySnapshot || !snap->copied) + newactive->as_snap = CopySnapshot(snap); + else + newactive->as_snap = snap; + newactive->as_next = ActiveSnapshot; newactive->as_level = GetCurrentTransactionNestLevel(); diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h index a82e53bb17..d52051a916 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 1.6 2009/10/02 17:57:30 alvherre Exp $ + * $PostgreSQL: pgsql/src/include/utils/snapmgr.h,v 1.7 2009/10/07 16:27:18 alvherre Exp $ * *------------------------------------------------------------------------- */ @@ -26,7 +26,6 @@ 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/triggers.out b/src/test/regress/expected/triggers.out index 2a5cb909d7..c0b7645600 100644 --- a/src/test/regress/expected/triggers.out +++ b/src/test/regress/expected/triggers.out @@ -537,6 +537,37 @@ NOTICE: row 1 not changed NOTICE: row 2 not changed DROP TABLE trigger_test; DROP FUNCTION mytrigger(); +-- Test snapshot management in serializable transactions involving triggers +-- per bug report in 6bc73d4c0910042358k3d1adff3qa36f8df75198ecea@mail.gmail.com +CREATE FUNCTION serializable_update_trig() RETURNS trigger LANGUAGE plpgsql AS +$$ +declare + rec record; +begin + new.description = 'updated in trigger'; + return new; +end; +$$; +CREATE TABLE serializable_update_tab ( + id int, + filler text, + description text +); +CREATE TRIGGER serializable_update_trig BEFORE UPDATE ON serializable_update_tab + FOR EACH ROW EXECUTE PROCEDURE serializable_update_trig(); +INSERT INTO serializable_update_tab SELECT a, repeat('xyzxz', 100), 'new' + FROM generate_series(1, 50) a; +BEGIN; +SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; +UPDATE serializable_update_tab SET description = 'no no', id = 1 WHERE id = 1; +COMMIT; +SELECT description FROM serializable_update_tab WHERE id = 1; + description +-------------------- + updated in trigger +(1 row) + +DROP TABLE serializable_update_tab; -- minimal update trigger CREATE TABLE min_updates_test ( f1 text, diff --git a/src/test/regress/sql/triggers.sql b/src/test/regress/sql/triggers.sql index 8530030ef8..878adbb0d4 100644 --- a/src/test/regress/sql/triggers.sql +++ b/src/test/regress/sql/triggers.sql @@ -416,6 +416,36 @@ DROP TABLE trigger_test; DROP FUNCTION mytrigger(); +-- Test snapshot management in serializable transactions involving triggers +-- per bug report in 6bc73d4c0910042358k3d1adff3qa36f8df75198ecea@mail.gmail.com +CREATE FUNCTION serializable_update_trig() RETURNS trigger LANGUAGE plpgsql AS +$$ +declare + rec record; +begin + new.description = 'updated in trigger'; + return new; +end; +$$; + +CREATE TABLE serializable_update_tab ( + id int, + filler text, + description text +); + +CREATE TRIGGER serializable_update_trig BEFORE UPDATE ON serializable_update_tab + FOR EACH ROW EXECUTE PROCEDURE serializable_update_trig(); + +INSERT INTO serializable_update_tab SELECT a, repeat('xyzxz', 100), 'new' + FROM generate_series(1, 50) a; + +BEGIN; +SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; +UPDATE serializable_update_tab SET description = 'no no', id = 1 WHERE id = 1; +COMMIT; +SELECT description FROM serializable_update_tab WHERE id = 1; +DROP TABLE serializable_update_tab; -- minimal update trigger -- 2.40.0