Do not re-do permission checks on range table for parallel worker (ba…

…belfish-for-postgresql#233)

With current design of postgres, workflow of parallel worker looks like something below:

```
-- main node
ExecutorRun
 standard_ExecutorStart
  InitPlan
   ExecCheckRTPerms <-- does the permission check on all the range table entries from planner stmt
 standard_ExecutorRun
  ExecutePlan
  .
  .
  .
  ExecGather
   gather_getnext
    -- spawns initialises and run parallel workers
  .
  .
  .
-- parallel worker
ParallelQueryMain
 ExecutorRun
  standard_ExecutorStart
   InitPlan
    ExecCheckRTPerms <- redo the permission check on same set of table
 standard_ExecutorRun
 .
 .
 .
```
Here, Main worker would not have spawned the worker if there is any permission check failures on any of the range table. And parallel worker is again doing the permission check on same set of tables which is kind of redundant. So this commit avoid that unnecessary permission check.

This change is also helpful when select query or subquery involves T-SQL temp tables. Currently, Babelfish is throwing error like "relation with OID 19401 does not exist" because metadata for temp tables is being stored in ENR metadata (which is backend memory) and is not being shared with parallel worker. So this changes will also avoid such error for temp table from parallel worker.

Task: BABEL-4450
Signed-off-by: Dipesh Dhameliya <[email protected]>

src/backend/executor/execMain.c

@@ -53,6 +53,7 @@
 #include "jit/jit.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "parser/parser.h"
 #include "parser/parsetree.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
@@ -814,9 +815,10 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	int			i;
 
 	/*
-	 * Do permissions checks
+	 * Do permissions checks if not parallel worker
 	 */
-	ExecCheckRTPerms(rangeTable, true);
+	if (!(sql_dialect == SQL_DIALECT_TSQL && IsParallelWorker()))
+		ExecCheckRTPerms(rangeTable, true);
 
 	/*
 	 * initialize the node's execution state