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michaelpqmichaelpq
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Simplify restriction handling of two-phase commit for temporary objects
There were two flags used to track the access to temporary tables and to the temporary namespace of a session which are used to restrict PREPARE TRANSACTION, however the first control flag is a concept included in the second. This removes the flag for temporary table tracking, keeping around only the one at namespace level. Author: Michael Paquier Reviewed-by: Álvaro Herrera Discussion: https://postgr.es/m/20190118053126.GH1883@paquier.xyz
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7 files changed

+25
-38
lines changed

7 files changed

+25
-38
lines changed

‎src/backend/access/common/relation.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -71,7 +71,7 @@ relation_open(Oid relationId, LOCKMODE lockmode)
7171

7272
/* Make note that we've accessed a temporary relation */
7373
if (RelationUsesLocalBuffers(r))
74-
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
74+
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
7575

7676
pgstat_initstats(r);
7777

@@ -121,7 +121,7 @@ try_relation_open(Oid relationId, LOCKMODE lockmode)
121121

122122
/* Make note that we've accessed a temporary relation */
123123
if (RelationUsesLocalBuffers(r))
124-
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
124+
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
125125

126126
pgstat_initstats(r);
127127

‎src/backend/access/transam/xact.c‎

Lines changed: 6 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -2266,29 +2266,22 @@ PrepareTransaction(void)
22662266
* clean up the source backend's local buffers and ON COMMIT state if the
22672267
* prepared xact includes a DROP of a temp table.
22682268
*
2269+
* Other objects types, like functions, operators or extensions, share the
2270+
* same restriction as they should not be created, locked or dropped as
2271+
* this can mess up with this session or even a follow-up session trying
2272+
* to use the same temporary namespace.
2273+
*
22692274
* We must check this after executing any ON COMMIT actions, because they
22702275
* might still access a temp relation.
22712276
*
22722277
* XXX In principle this could be relaxed to allow some useful special
22732278
* cases, such as a temp table created and dropped all within the
22742279
* transaction. That seems to require much more bookkeeping though.
22752280
*/
2276-
if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPREL))
2277-
ereport(ERROR,
2278-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2279-
errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
2280-
2281-
/*
2282-
* Similarly, PREPARE TRANSACTION is not allowed if the temporary
2283-
* namespace has been involved in this transaction as we cannot allow it
2284-
* to create, lock, or even drop objects within the temporary namespace
2285-
* as this can mess up with this session or even a follow-up session
2286-
* trying to use the same temporary namespace.
2287-
*/
22882281
if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPNAMESPACE))
22892282
ereport(ERROR,
22902283
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2291-
errmsg("cannot PREPARE a transaction that has operated on temporary namespace")));
2284+
errmsg("cannot PREPARE a transaction that has operated on temporary objects")));
22922285

22932286
/*
22942287
* Likewise, don't allow PREPARE after pg_export_snapshot. This could be

‎src/backend/commands/lockcmds.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -108,7 +108,7 @@ RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid, Oid oldrelid,
108108
*/
109109
relpersistence = get_rel_persistence(relid);
110110
if (relpersistence == RELPERSISTENCE_TEMP)
111-
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
111+
MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
112112

113113
/* Check permissions. */
114114
aclresult = LockTableAclCheck(relid, lockmode, GetUserId());

‎src/backend/commands/tablecmds.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -13642,7 +13642,7 @@ PreCommit_on_commit_actions(void)
1364213642
* relations, we can skip truncating ON COMMIT DELETE ROWS
1364313643
* tables, as they must still be empty.
1364413644
*/
13645-
if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPREL))
13645+
if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPNAMESPACE))
1364613646
oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
1364713647
break;
1364813648
case ONCOMMIT_DROP:

‎src/include/access/xact.h‎

Lines changed: 3 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -87,23 +87,17 @@ extern int synchronous_commit;
8787
extern int MyXactFlags;
8888

8989
/*
90-
* XACT_FLAGS_ACCESSEDTEMPREL - set when a temporary relation is accessed. We
91-
* don't allow PREPARE TRANSACTION in that case.
90+
* XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary object is accessed.
91+
* We don't allow PREPARE TRANSACTION in that case.
9292
*/
93-
#define XACT_FLAGS_ACCESSEDTEMPREL (1U << 0)
93+
#define XACT_FLAGS_ACCESSEDTEMPNAMESPACE (1U << 0)
9494

9595
/*
9696
* XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK - records whether the top level xact
9797
* logged any Access Exclusive Locks.
9898
*/
9999
#define XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK (1U << 1)
100100

101-
/*
102-
* XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary namespace is
103-
* accessed. We don't allow PREPARE TRANSACTION in that case.
104-
*/
105-
#define XACT_FLAGS_ACCESSEDTEMPNAMESPACE (1U << 2)
106-
107101
/*
108102
* start- and end-of-transaction callbacks for dynamically loaded modules
109103
*/

‎src/test/modules/test_extensions/expected/test_extensions.out‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -148,7 +148,7 @@ SELECT create_extension_with_temp_schema();
148148
(1 row)
149149

150150
PREPARE TRANSACTION 'twophase_extension';
151-
ERROR: cannot PREPARE a transaction that has operated on temporary namespace
151+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
152152
-- Clean up
153153
DROP TABLE test_ext4_tab;
154154
DROP FUNCTION create_extension_with_temp_schema();

‎src/test/regress/expected/temp.out‎

Lines changed: 11 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -310,32 +310,32 @@ begin;
310310
create function pg_temp.twophase_func() returns void as
311311
$$ select '2pc_func'::text $$ language sql;
312312
prepare transaction 'twophase_func';
313-
ERROR: cannot PREPARE a transaction that has operated on temporary namespace
313+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
314314
-- Function drop
315315
create function pg_temp.twophase_func() returns void as
316316
$$ select '2pc_func'::text $$ language sql;
317317
begin;
318318
drop function pg_temp.twophase_func();
319319
prepare transaction 'twophase_func';
320-
ERROR: cannot PREPARE a transaction that has operated on temporary namespace
320+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
321321
-- Operator creation
322322
begin;
323323
create operator pg_temp.@@ (leftarg = int4, rightarg = int4, procedure = int4mi);
324324
prepare transaction 'twophase_operator';
325-
ERROR: cannot PREPARE a transaction that has operated on temporary namespace
325+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
326326
-- These generate errors about temporary tables.
327327
begin;
328328
create type pg_temp.twophase_type as (a int);
329329
prepare transaction 'twophase_type';
330-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
330+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
331331
begin;
332332
create view pg_temp.twophase_view as select 1;
333333
prepare transaction 'twophase_view';
334-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
334+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
335335
begin;
336336
create sequence pg_temp.twophase_seq;
337337
prepare transaction 'twophase_sequence';
338-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
338+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
339339
-- Temporary tables cannot be used with two-phase commit.
340340
create temp table twophase_tab (a int);
341341
begin;
@@ -345,19 +345,19 @@ select a from twophase_tab;
345345
(0 rows)
346346

347347
prepare transaction 'twophase_tab';
348-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
348+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
349349
begin;
350350
insert into twophase_tab values (1);
351351
prepare transaction 'twophase_tab';
352-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
352+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
353353
begin;
354354
lock twophase_tab in access exclusive mode;
355355
prepare transaction 'twophase_tab';
356-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
356+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
357357
begin;
358358
drop table twophase_tab;
359359
prepare transaction 'twophase_tab';
360-
ERROR: cannot PREPARE a transaction that has operated on temporary tables
360+
ERROR: cannot PREPARE a transaction that has operated on temporary objects
361361
-- Corner case: current_schema may create a temporary schema if namespace
362362
-- creation is pending, so check after that. First reset the connection
363363
-- to remove the temporary namespace, and make sure that non-parallel plans
@@ -374,4 +374,4 @@ SELECT current_schema() ~ 'pg_temp' AS is_temp_schema;
374374
(1 row)
375375

376376
PREPARE TRANSACTION 'twophase_search';
377-
ERROR: cannot PREPARE a transaction that has operated on temporary namespace
377+
ERROR: cannot PREPARE a transaction that has operated on temporary objects

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