On 09/08/2010 10:02 AM, Tom Lane wrote: > Alvaro Herrera <alvhe...@commandprompt.com> writes: >> Excerpts from Tom Lane's message of mié sep 08 12:12:31 -0400 2010: >>> AFAIR it doesn't keep the first snapshot around. If it did, most of >>> your work on snapshot list trimming would have been useless, no? > >> That's my point precisely. The name "IsolationUsesXactSnapshot" makes >> it sound like it applies to any transaction that uses snapshots for >> isolation, doesn't it? > > I don't think so, at least not when compared to the alternative > IsolationUsesStmtSnapshot.
The attached patch is updated for the various comments, as well as some wording tweaks by me. If there are no objections I'd like to commit this in a day or two. Joe -- Joe Conway credativ LLC: http://www.credativ.us Linux, PostgreSQL, and general Open Source Training, Service, Consulting, & 24x7 Support
? src/backend/parser/parse.h
Index: src/backend/access/heap/heapam.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/access/heap/heapam.c,v
retrieving revision 1.293
diff -c -r1.293 heapam.c
*** src/backend/access/heap/heapam.c 29 Jul 2010 16:14:36 -0000 1.293
--- src/backend/access/heap/heapam.c 9 Sep 2010 16:03:18 -0000
***************
*** 2173,2179 ****
if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
! /* Perform additional check for serializable RI updates */
if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
result = HeapTupleUpdated;
}
--- 2173,2179 ----
if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
! /* Perform additional check for transaction-snapshot mode RI updates */
if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
result = HeapTupleUpdated;
}
***************
*** 2525,2531 ****
if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
! /* Perform additional check for serializable RI updates */
if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
result = HeapTupleUpdated;
}
--- 2525,2531 ----
if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
{
! /* Perform additional check for transaction-snapshot mode RI updates */
if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
result = HeapTupleUpdated;
}
Index: src/backend/catalog/index.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/catalog/index.c,v
retrieving revision 1.338
diff -c -r1.338 index.c
*** src/backend/catalog/index.c 13 Aug 2010 20:10:50 -0000 1.338
--- src/backend/catalog/index.c 9 Sep 2010 16:03:18 -0000
***************
*** 2049,2055 ****
*
* After completing validate_index(), we wait until all transactions that
* were alive at the time of the reference snapshot are gone; this is
! * necessary to be sure there are none left with a serializable snapshot
* older than the reference (and hence possibly able to see tuples we did
* not index). Then we mark the index "indisvalid" and commit. Subsequent
* transactions will be able to use it for queries.
--- 2049,2055 ----
*
* After completing validate_index(), we wait until all transactions that
* were alive at the time of the reference snapshot are gone; this is
! * necessary to be sure there are none left with a transaction snapshot
* older than the reference (and hence possibly able to see tuples we did
* not index). Then we mark the index "indisvalid" and commit. Subsequent
* transactions will be able to use it for queries.
Index: src/backend/commands/trigger.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/commands/trigger.c,v
retrieving revision 1.265
diff -c -r1.265 trigger.c
*** src/backend/commands/trigger.c 19 Aug 2010 15:46:18 -0000 1.265
--- src/backend/commands/trigger.c 9 Sep 2010 16:03:18 -0000
***************
*** 2387,2393 ****
case HeapTupleUpdated:
ReleaseBuffer(buffer);
! if (IsXactIsoLevelSerializable)
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
--- 2387,2393 ----
case HeapTupleUpdated:
ReleaseBuffer(buffer);
! if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
Index: src/backend/executor/execMain.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/execMain.c,v
retrieving revision 1.354
diff -c -r1.354 execMain.c
*** src/backend/executor/execMain.c 5 Aug 2010 14:45:02 -0000 1.354
--- src/backend/executor/execMain.c 9 Sep 2010 16:03:19 -0000
***************
*** 1554,1560 ****
case HeapTupleUpdated:
ReleaseBuffer(buffer);
! if (IsXactIsoLevelSerializable)
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
--- 1554,1560 ----
case HeapTupleUpdated:
ReleaseBuffer(buffer);
! if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
Index: src/backend/executor/nodeLockRows.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/nodeLockRows.c,v
retrieving revision 1.6
diff -c -r1.6 nodeLockRows.c
*** src/backend/executor/nodeLockRows.c 28 Jul 2010 17:21:56 -0000 1.6
--- src/backend/executor/nodeLockRows.c 9 Sep 2010 16:03:19 -0000
***************
*** 130,136 ****
break;
case HeapTupleUpdated:
! if (IsXactIsoLevelSerializable)
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
--- 130,136 ----
break;
case HeapTupleUpdated:
! if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
Index: src/backend/executor/nodeModifyTable.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/executor/nodeModifyTable.c,v
retrieving revision 1.9
diff -c -r1.9 nodeModifyTable.c
*** src/backend/executor/nodeModifyTable.c 18 Aug 2010 21:52:24 -0000 1.9
--- src/backend/executor/nodeModifyTable.c 9 Sep 2010 16:03:19 -0000
***************
*** 310,316 ****
* Note: if es_crosscheck_snapshot isn't InvalidSnapshot, we check that
* the row to be deleted is visible to that snapshot, and throw a can't-
* serialize error if not. This is a special-case behavior needed for
! * referential integrity updates in serializable transactions.
*/
ldelete:;
result = heap_delete(resultRelationDesc, tupleid,
--- 310,316 ----
* Note: if es_crosscheck_snapshot isn't InvalidSnapshot, we check that
* the row to be deleted is visible to that snapshot, and throw a can't-
* serialize error if not. This is a special-case behavior needed for
! * referential integrity updates in transaction-snapshot mode transactions.
*/
ldelete:;
result = heap_delete(resultRelationDesc, tupleid,
***************
*** 328,334 ****
break;
case HeapTupleUpdated:
! if (IsXactIsoLevelSerializable)
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
--- 328,334 ----
break;
case HeapTupleUpdated:
! if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
***************
*** 499,505 ****
* Note: if es_crosscheck_snapshot isn't InvalidSnapshot, we check that
* the row to be updated is visible to that snapshot, and throw a can't-
* serialize error if not. This is a special-case behavior needed for
! * referential integrity updates in serializable transactions.
*/
result = heap_update(resultRelationDesc, tupleid, tuple,
&update_ctid, &update_xmax,
--- 499,505 ----
* Note: if es_crosscheck_snapshot isn't InvalidSnapshot, we check that
* the row to be updated is visible to that snapshot, and throw a can't-
* serialize error if not. This is a special-case behavior needed for
! * referential integrity updates in transaction-snapshot mode transactions.
*/
result = heap_update(resultRelationDesc, tupleid, tuple,
&update_ctid, &update_xmax,
***************
*** 516,522 ****
break;
case HeapTupleUpdated:
! if (IsXactIsoLevelSerializable)
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
--- 516,522 ----
break;
case HeapTupleUpdated:
! if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
Index: src/backend/tcop/postgres.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/tcop/postgres.c,v
retrieving revision 1.596
diff -c -r1.596 postgres.c
*** src/backend/tcop/postgres.c 12 Aug 2010 23:24:54 -0000 1.596
--- src/backend/tcop/postgres.c 9 Sep 2010 16:03:19 -0000
***************
*** 2802,2808 ****
*
* PROCSIG_RECOVERY_CONFLICT_SNAPSHOT if no snapshots are held
* by parent transactions and the transaction is not
! * serializable
*
* PROCSIG_RECOVERY_CONFLICT_TABLESPACE if no temp files or
* cursors open in parent transactions
--- 2802,2808 ----
*
* PROCSIG_RECOVERY_CONFLICT_SNAPSHOT if no snapshots are held
* by parent transactions and the transaction is not
! * transaction-snapshot mode
*
* PROCSIG_RECOVERY_CONFLICT_TABLESPACE if no temp files or
* cursors open in parent transactions
Index: src/backend/tcop/pquery.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/tcop/pquery.c,v
retrieving revision 1.137
diff -c -r1.137 pquery.c
*** src/backend/tcop/pquery.c 26 Feb 2010 02:01:02 -0000 1.137
--- src/backend/tcop/pquery.c 9 Sep 2010 16:03:19 -0000
***************
*** 1163,1170 ****
* Set snapshot if utility stmt needs one. Most reliable way to do this
* seems to be to enumerate those that do not need one; this is a short
* list. Transaction control, LOCK, and SET must *not* set a snapshot
! * since they need to be executable at the start of a serializable
! * transaction without freezing a snapshot. By extension we allow SHOW
* not to set a snapshot. The other stmts listed are just efficiency
* hacks. Beware of listing anything that can modify the database --- if,
* say, it has to update an index with expressions that invoke
--- 1163,1170 ----
* Set snapshot if utility stmt needs one. Most reliable way to do this
* seems to be to enumerate those that do not need one; this is a short
* list. Transaction control, LOCK, and SET must *not* set a snapshot
! * since they need to be executable at the start of a transaction-snapshot
! * mode transaction without freezing a snapshot. By extension we allow SHOW
* not to set a snapshot. The other stmts listed are just efficiency
* hacks. Beware of listing anything that can modify the database --- if,
* say, it has to update an index with expressions that invoke
Index: src/backend/utils/adt/ri_triggers.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/utils/adt/ri_triggers.c,v
retrieving revision 1.120
diff -c -r1.120 ri_triggers.c
*** src/backend/utils/adt/ri_triggers.c 28 Jul 2010 05:22:24 -0000 1.120
--- src/backend/utils/adt/ri_triggers.c 9 Sep 2010 16:03:19 -0000
***************
*** 2784,2793 ****
/*
* Run the plan. For safety we force a current snapshot to be used. (In
! * serializable mode, this arguably violates serializability, but we
! * really haven't got much choice.) We don't need to register the
! * snapshot, because SPI_execute_snapshot will see to it. We need at most
! * one tuple returned, so pass limit = 1.
*/
spi_result = SPI_execute_snapshot(qplan,
NULL, NULL,
--- 2784,2793 ----
/*
* Run the plan. For safety we force a current snapshot to be used. (In
! * transaction-snapshot mode, this arguably violates transaction
! * isolation rules, but we really haven't got much choice.)
! * We don't need to register the snapshot, because SPI_execute_snapshot
! * will see to it. We need at most one tuple returned, so pass limit = 1.
*/
spi_result = SPI_execute_snapshot(qplan,
NULL, NULL,
***************
*** 3332,3346 ****
/*
* In READ COMMITTED mode, we just need to use an up-to-date regular
* snapshot, and we will see all rows that could be interesting. But in
! * SERIALIZABLE mode, we can't change the transaction snapshot. If the
! * caller passes detectNewRows == false then it's okay to do the query
* with the transaction snapshot; otherwise we use a current snapshot, and
* tell the executor to error out if it finds any rows under the current
* snapshot that wouldn't be visible per the transaction snapshot. Note
* that SPI_execute_snapshot will register the snapshots, so we don't need
* to bother here.
*/
! if (IsXactIsoLevelSerializable && detectNewRows)
{
CommandCounterIncrement(); /* be sure all my own work is visible */
test_snapshot = GetLatestSnapshot();
--- 3332,3346 ----
/*
* In READ COMMITTED mode, we just need to use an up-to-date regular
* snapshot, and we will see all rows that could be interesting. But in
! * transaction-snapshot mode, we can't change the transaction snapshot.
! * If the caller passes detectNewRows == false then it's okay to do the query
* with the transaction snapshot; otherwise we use a current snapshot, and
* tell the executor to error out if it finds any rows under the current
* snapshot that wouldn't be visible per the transaction snapshot. Note
* that SPI_execute_snapshot will register the snapshots, so we don't need
* to bother here.
*/
! if (IsolationUsesXactSnapshot() && detectNewRows)
{
CommandCounterIncrement(); /* be sure all my own work is visible */
test_snapshot = GetLatestSnapshot();
Index: src/backend/utils/time/snapmgr.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/utils/time/snapmgr.c,v
retrieving revision 1.15
diff -c -r1.15 snapmgr.c
*** src/backend/utils/time/snapmgr.c 26 Feb 2010 02:01:15 -0000 1.15
--- src/backend/utils/time/snapmgr.c 9 Sep 2010 16:03:19 -0000
***************
*** 37,46 ****
/*
! * CurrentSnapshot points to the only snapshot taken in a serializable
! * transaction, and to the latest one taken in a read-committed transaction.
* SecondarySnapshot is a snapshot that's always up-to-date as of the current
! * instant, even on a serializable transaction. It should only be used for
* special-purpose code (say, RI checking.)
*
* These SnapshotData structs are static to simplify memory allocation
--- 37,46 ----
/*
! * CurrentSnapshot points to the only snapshot taken in transaction-snapshot
! * mode, and to the latest one taken in a read-committed transaction.
* SecondarySnapshot is a snapshot that's always up-to-date as of the current
! * instant, even in transaction-snapshot mode. It should only be used for
* special-purpose code (say, RI checking.)
*
* These SnapshotData structs are static to simplify memory allocation
***************
*** 97,107 ****
bool FirstSnapshotSet = false;
/*
! * Remembers whether this transaction registered a serializable snapshot at
* start. We cannot trust FirstSnapshotSet in combination with
! * IsXactIsoLevelSerializable, because GUC may be reset before us.
*/
! static bool registered_serializable = false;
static Snapshot CopySnapshot(Snapshot snapshot);
--- 97,107 ----
bool FirstSnapshotSet = false;
/*
! * Remembers whether this transaction registered a transaction snapshot at
* start. We cannot trust FirstSnapshotSet in combination with
! * IsolationUsesXactSnapshot(), because GUC may be reset before us.
*/
! static bool registered_xact_snapshot = false;
static Snapshot CopySnapshot(Snapshot snapshot);
***************
*** 130,150 ****
FirstSnapshotSet = true;
/*
! * In serializable mode, the first snapshot must live until end of
! * xact regardless of what the caller does with it, so we must
* register it internally here and unregister it at end of xact.
*/
! if (IsXactIsoLevelSerializable)
{
CurrentSnapshot = RegisterSnapshotOnOwner(CurrentSnapshot,
TopTransactionResourceOwner);
! registered_serializable = true;
}
return CurrentSnapshot;
}
! if (IsXactIsoLevelSerializable)
return CurrentSnapshot;
CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
--- 130,150 ----
FirstSnapshotSet = true;
/*
! * In transaction-snapshot mode, the first snapshot must live until
! * end of xact regardless of what the caller does with it, so we must
* register it internally here and unregister it at end of xact.
*/
! if (IsolationUsesXactSnapshot())
{
CurrentSnapshot = RegisterSnapshotOnOwner(CurrentSnapshot,
TopTransactionResourceOwner);
! registered_xact_snapshot = true;
}
return CurrentSnapshot;
}
! if (IsolationUsesXactSnapshot())
return CurrentSnapshot;
CurrentSnapshot = GetSnapshotData(&CurrentSnapshotData);
***************
*** 155,161 ****
/*
* GetLatestSnapshot
* Get a snapshot that is up-to-date as of the current instant,
! * even if we are executing in SERIALIZABLE mode.
*/
Snapshot
GetLatestSnapshot(void)
--- 155,161 ----
/*
* GetLatestSnapshot
* Get a snapshot that is up-to-date as of the current instant,
! * even if we are executing in transaction-snapshot mode.
*/
Snapshot
GetLatestSnapshot(void)
***************
*** 515,527 ****
AtEarlyCommit_Snapshot(void)
{
/*
! * On a serializable transaction we must unregister our private refcount
! * to the serializable snapshot.
*/
! if (registered_serializable)
UnregisterSnapshotFromOwner(CurrentSnapshot,
TopTransactionResourceOwner);
! registered_serializable = false;
}
--- 515,527 ----
AtEarlyCommit_Snapshot(void)
{
/*
! * In transaction-snapshot mode we must unregister our private refcount
! * to the transaction-snapshot.
*/
! if (registered_xact_snapshot)
UnregisterSnapshotFromOwner(CurrentSnapshot,
TopTransactionResourceOwner);
! registered_xact_snapshot = false;
}
***************
*** 557,561 ****
SecondarySnapshot = NULL;
FirstSnapshotSet = false;
! registered_serializable = false;
}
--- 557,561 ----
SecondarySnapshot = NULL;
FirstSnapshotSet = false;
! registered_xact_snapshot = false;
}
Index: src/include/access/xact.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/access/xact.h,v
retrieving revision 1.103
diff -c -r1.103 xact.h
*** src/include/access/xact.h 26 Feb 2010 02:01:21 -0000 1.103
--- src/include/access/xact.h 9 Sep 2010 16:03:20 -0000
***************
*** 35,41 ****
* We only implement two isolation levels internally. This macro should
* be used to check which one is selected.
*/
! #define IsXactIsoLevelSerializable (XactIsoLevel >= XACT_REPEATABLE_READ)
/* Xact read-only state */
extern bool DefaultXactReadOnly;
--- 35,41 ----
* We only implement two isolation levels internally. This macro should
* be used to check which one is selected.
*/
! #define IsolationUsesXactSnapshot() (XactIsoLevel >= XACT_REPEATABLE_READ)
/* Xact read-only state */
extern bool DefaultXactReadOnly;
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