diff options
Diffstat (limited to 'src/backend/executor/execMain.c')
| -rw-r--r-- | src/backend/executor/execMain.c | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c index df4da3faa97..26793eecf48 100644 --- a/src/backend/executor/execMain.c +++ b/src/backend/executor/execMain.c @@ -147,8 +147,20 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags) /* * If the transaction is read-only, we need to check if any writes are * planned to non-temporary tables. EXPLAIN is considered read-only. + * + * Don't allow writes in parallel mode. Supporting UPDATE and DELETE would + * require (a) storing the combocid hash in shared memory, rather than + * synchronizing it just once at the start of parallelism, and (b) an + * alternative to heap_update()'s reliance on xmax for mutual exclusion. + * INSERT may have no such troubles, but we forbid it to simplify the + * checks. + * + * We have lower-level defenses in CommandCounterIncrement and elsewhere + * against performing unsafe operations in parallel mode, but this gives + * a more user-friendly error message. */ - if (XactReadOnly && !(eflags & EXEC_FLAG_EXPLAIN_ONLY)) + if ((XactReadOnly || IsInParallelMode()) && + !(eflags & EXEC_FLAG_EXPLAIN_ONLY)) ExecCheckXactReadOnly(queryDesc->plannedstmt); /* @@ -691,18 +703,23 @@ ExecCheckRTEPerms(RangeTblEntry *rte) } /* - * Check that the query does not imply any writes to non-temp tables. + * Check that the query does not imply any writes to non-temp tables; + * unless we're in parallel mode, in which case don't even allow writes + * to temp tables. * * Note: in a Hot Standby slave this would need to reject writes to temp - * tables as well; but an HS slave can't have created any temp tables - * in the first place, so no need to check that. + * tables just as we do in parallel mode; but an HS slave can't have created + * any temp tables in the first place, so no need to check that. */ static void ExecCheckXactReadOnly(PlannedStmt *plannedstmt) { ListCell *l; - /* Fail if write permissions are requested on any non-temp table */ + /* + * Fail if write permissions are requested in parallel mode for + * table (temp or non-temp), otherwise fail for any non-temp table. + */ foreach(l, plannedstmt->rtable) { RangeTblEntry *rte = (RangeTblEntry *) lfirst(l); @@ -718,6 +735,9 @@ ExecCheckXactReadOnly(PlannedStmt *plannedstmt) PreventCommandIfReadOnly(CreateCommandTag((Node *) plannedstmt)); } + + if (plannedstmt->commandType != CMD_SELECT || plannedstmt->hasModifyingCTE) + PreventCommandIfParallelMode(CreateCommandTag((Node *) plannedstmt)); } |