Fixed error code difference occurring due to parallel worker enforced (…

…#260)

When any error raised from parallel worker then Postgres by default does not share message_id (part of edata) to
leader worker. Babelfish's error mapping framework relies on message_id to map to correct T-SQL error code. But
since it is no more available to leader worker, T-SQL error code would not be found and default error code will be used.
This will also affect the transactional behaviour of given error.

In order to fix this issue, we need to store if given worker is spawned in the context of Babelfish or not to share error
message_id. Hence, this changes made changes in two data structure namely Port and FixedParallelState to store
context about Babelfish

Extension changes: babelfish-for-postgresql/babelfish_extensions#2047
Task: BABEL-4539
Signed-off-by: Dipesh Dhameliya <[email protected]>

src/backend/access/transam/parallel.c

@@ -96,6 +96,9 @@ typedef struct FixedParallelState
 	TimestampTz stmt_ts;
 	SerializableXactHandle serializable_xact_handle;
 
+	/* Track if parallel worker is spawned in the context of Babelfish */
+	bool babelfish_context;
+
 	/* Mutex protects remaining fields. */
 	slock_t		mutex;
 
@@ -332,6 +335,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
 	fps->xact_ts = GetCurrentTransactionStartTimestamp();
 	fps->stmt_ts = GetCurrentStatementStartTimestamp();
 	fps->serializable_xact_handle = ShareSerializableXact();
+	fps->babelfish_context = MyProcPort->is_tds_conn;
 	SpinLockInit(&fps->mutex);
 	fps->last_xlog_end = 0;
 	shm_toc_insert(pcxt->toc, PARALLEL_KEY_FIXED, fps);
@@ -1595,3 +1599,13 @@ LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
 	return (parallel_worker_main_type)
 		load_external_function(libraryname, funcname, true, NULL);
 }
+
+/*
+ * IsBabelfishParallelWorker - return bool based on whether given worker is
+ * spawned in Babelfish context.
+ */
+bool
+IsBabelfishParallelWorker(void)
+{
+	return (IsParallelWorker() && MyFixedParallelState->babelfish_context);
+}

src/backend/executor/execMain.c

@@ -818,9 +818,9 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 	int			i;
 
 	/*
-	 * Do permissions checks if not parallel worker
+	 * Do permissions checks if not Babelfish parallel worker
 	 */
-	if (!(sql_dialect == SQL_DIALECT_TSQL && IsParallelWorker()))
+	if (!IsBabelfishParallelWorker())
 		ExecCheckRTPerms(rangeTable, true);
 
 	/*

src/backend/libpq/pqmq.c

@@ -310,6 +310,16 @@ pq_parse_errornotice(StringInfo msg, ErrorData *edata)
 			case PG_DIAG_SOURCE_FUNCTION:
 				edata->funcname = pstrdup(value);
 				break;
+			case PG_DIAG_MESSAGE_ID:
+				if (MyProcPort->is_tds_conn)
+				{
+					edata->message_id = (const char *) pstrdup(value);
+				}
+				else
+				{
+					elog(ERROR, "Unexpected error field message_id is found");
+				}
+				break;
 			default:
 				elog(ERROR, "unrecognized error field code: %d", (int) code);
 				break;

src/backend/utils/error/elog.c

@@ -67,6 +67,7 @@
 #endif
 
 #include "access/transam.h"
+#include "access/parallel.h"
 #include "access/xact.h"
 #include "libpq/libpq.h"
 #include "libpq/pqformat.h"
@@ -1718,6 +1719,14 @@ ThrowErrorData(ErrorData *edata)
 	if (edata->internalquery)
 		newedata->internalquery = pstrdup(edata->internalquery);
 
+	/*
+	 * Generally, vanilla postgres does not share messaged_id with leader node from
+	 * parallel worker. But case of Babelfish where message_id is needed to find
+	 * T-SQL error code; below hook is defined to handle message_id for Babelfish. 
+	 */
+	if (edata->message_id)
+		newedata->message_id = (const char *) pstrdup(edata->message_id);
+
 	MemoryContextSwitchTo(oldcontext);
 	recursion_depth--;
 
@@ -3250,6 +3259,15 @@ send_message_to_frontend(ErrorData *edata)
 			err_sendstring(&msgbuf, edata->funcname);
 		}
 
+		if (IsBabelfishParallelWorker())
+		{
+			if (edata->message_id)
+			{
+				pq_sendbyte(&msgbuf, PG_DIAG_MESSAGE_ID);
+				err_sendstring(&msgbuf, edata->message_id);
+			}
+		}
+
 		pq_sendbyte(&msgbuf, '\0'); /* terminator */
 
 		pq_endmessage(&msgbuf);

src/include/access/parallel.h

@@ -79,4 +79,7 @@ extern void ParallelWorkerReportLastRecEnd(XLogRecPtr last_xlog_end);
 
 extern void ParallelWorkerMain(Datum main_arg);
 
+/* Below helpers are added to support parallel workers in Babelfish context */
+extern bool IsBabelfishParallelWorker(void);
+
 #endif							/* PARALLEL_H */

src/include/libpq/libpq-be.h

@@ -250,6 +250,7 @@ typedef struct Port
 	SSL		   *ssl;
 	X509	   *peer;
 #endif
+	bool		is_tds_conn;
 } Port;
 
 #ifdef USE_SSL

src/include/postgres_ext.h

@@ -70,5 +70,6 @@ typedef PG_INT64_TYPE pg_int64;
 #define PG_DIAG_SOURCE_FILE		'F'
 #define PG_DIAG_SOURCE_LINE		'L'
 #define PG_DIAG_SOURCE_FUNCTION 'R'
+#define PG_DIAG_MESSAGE_ID      'I'
 
 #endif							/* POSTGRES_EXT_H */