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Commit2eb34ac

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Fix problems with "read only query" checks, and refactor the code.
Previously, check_xact_readonly() was responsible for determiningwhich types of queries could not be run in a read-only transaction,standard_ProcessUtility() was responsibility for prohibiting thingswhich were allowed in read only transactions but not in recovery, andutility commands were basically prohibited in bulk in parallel mode bycalls to CommandIsReadOnly() in functions.c and spi.c. This situationwas confusing and error-prone. Accordingly, move all the checks to anew function ClassifyUtilityCommandAsReadOnly(), which determines thedegree to which a given statement is read only.In the old code, check_xact_readonly() inadvertently failed to handleseveral statement types that actually should have been prohibited,specifically T_CreatePolicyStmt, T_AlterPolicyStmt, T_CreateAmStmt,T_CreateStatsStmt, T_AlterStatsStmt, and T_AlterCollationStmt. As aresult, thes statements were erroneously allowed in read onlytransactions, parallel queries, and standby operation. Generally, theywould fail anyway due to some lower-level error check, but weshouldn't rely on that. In the new code structure, future omissionsof this type should cause ClassifyUtilityCommandAsReadOnly() tocomplain about an unrecognized node type.As a fringe benefit, this means we can allow certain types of utilitycommands in parallel mode, where it's safe to do so. This allowsALTER SYSTEM, CALL, DO, CHECKPOINT, COPY FROM, EXPLAIN, and SHOW.It might be possible to allow additional commands with more workand thought.Along the way, document the thinking process behind the current setof checks, as per discussion especially with Peter Eisentraut. Thereis some interest in revising some of these rules, but that seemslike a job for another patch.Patch by me, reviewed by Tom Lane, Stephen Frost, and PeterEisentraut.Discussion:http://postgr.es/m/CA+TgmoZ_rLqJt5sYkvh+JpQnfX0Y+B2R+qfi820xNih6x-FQOQ@mail.gmail.com
1 parent0db7c67 commit2eb34ac

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6 files changed

+292
-135
lines changed

6 files changed

+292
-135
lines changed

‎src/backend/commands/copy.c

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1064,7 +1064,6 @@ DoCopy(ParseState *pstate, const CopyStmt *stmt,
10641064
/* check read-only transaction and parallel mode */
10651065
if (XactReadOnly&& !rel->rd_islocaltemp)
10661066
PreventCommandIfReadOnly("COPY FROM");
1067-
PreventCommandIfParallelMode("COPY FROM");
10681067

10691068
cstate=BeginCopyFrom(pstate,rel,stmt->filename,stmt->is_program,
10701069
NULL,stmt->attlist,stmt->options);

‎src/backend/commands/lockcmds.c

Lines changed: 0 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -42,17 +42,6 @@ LockTableCommand(LockStmt *lockstmt)
4242
{
4343
ListCell*p;
4444

45-
/*---------
46-
* During recovery we only accept these variations:
47-
* LOCK TABLE foo IN ACCESS SHARE MODE
48-
* LOCK TABLE foo IN ROW SHARE MODE
49-
* LOCK TABLE foo IN ROW EXCLUSIVE MODE
50-
* This test must match the restrictions defined in LockAcquireExtended()
51-
*---------
52-
*/
53-
if (lockstmt->mode>RowExclusiveLock)
54-
PreventCommandDuringRecovery("LOCK TABLE");
55-
5645
/*
5746
* Iterate over the list and process the named relations one at a time
5847
*/

‎src/backend/executor/functions.c

Lines changed: 0 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -540,9 +540,6 @@ init_execution_state(List *queryTree_list,
540540
errmsg("%s is not allowed in a non-volatile function",
541541
CreateCommandTag((Node*)stmt))));
542542

543-
if (IsInParallelMode()&& !CommandIsReadOnly(stmt))
544-
PreventCommandIfParallelMode(CreateCommandTag((Node*)stmt));
545-
546543
/* OK, build the execution_state for this query */
547544
newes= (execution_state*)palloc(sizeof(execution_state));
548545
if (preves)

‎src/backend/executor/spi.c

Lines changed: 11 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -1450,14 +1450,13 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
14501450
portal->queryEnv=_SPI_current->queryEnv;
14511451

14521452
/*
1453-
* If told to be read-only, or in parallel mode, verify that this query is
1454-
* in fact read-only. This can't be done earlier because we need to look
1455-
* at the finished, planned queries. (In particular, we don't want to do
1456-
* it between GetCachedPlan and PortalDefineQuery, because throwing an
1457-
* error between those steps would result in leaking our plancache
1458-
* refcount.)
1453+
* If told to be read-only, we'd better check for read-only queries. This
1454+
* can't be done earlier because we need to look at the finished, planned
1455+
* queries. (In particular, we don't want to do it between GetCachedPlan
1456+
* and PortalDefineQuery, because throwing an error between those steps
1457+
* would result in leaking our plancache refcount.)
14591458
*/
1460-
if (read_only||IsInParallelMode())
1459+
if (read_only)
14611460
{
14621461
ListCell*lc;
14631462

@@ -1466,16 +1465,11 @@ SPI_cursor_open_internal(const char *name, SPIPlanPtr plan,
14661465
PlannedStmt*pstmt=lfirst_node(PlannedStmt,lc);
14671466

14681467
if (!CommandIsReadOnly(pstmt))
1469-
{
1470-
if (read_only)
1471-
ereport(ERROR,
1472-
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1473-
/* translator: %s is a SQL statement name */
1474-
errmsg("%s is not allowed in a non-volatile function",
1475-
CreateCommandTag((Node*)pstmt))));
1476-
else
1477-
PreventCommandIfParallelMode(CreateCommandTag((Node*)pstmt));
1478-
}
1468+
ereport(ERROR,
1469+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1470+
/* translator: %s is a SQL statement name */
1471+
errmsg("%s is not allowed in a non-volatile function",
1472+
CreateCommandTag((Node*)pstmt))));
14791473
}
14801474
}
14811475

@@ -2263,9 +2257,6 @@ _SPI_execute_plan(SPIPlanPtr plan, ParamListInfo paramLI,
22632257
errmsg("%s is not allowed in a non-volatile function",
22642258
CreateCommandTag((Node*)stmt))));
22652259

2266-
if (IsInParallelMode()&& !CommandIsReadOnly(stmt))
2267-
PreventCommandIfParallelMode(CreateCommandTag((Node*)stmt));
2268-
22692260
/*
22702261
* If not read-only mode, advance the command counter before each
22712262
* command and update the snapshot.

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