Pass the source text for a parallel query to the workers.

With this change, you can see the query that a parallel worker is
executing in pg_stat_activity, and if the worker crashes you can
see what query it was executing when it crashed.

Rafia Sabih, reviewed by Kuntal Ghosh and Amit Kapila and slightly
revised by me.

4 files changed, 29 insertions, 1 deletions

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index a66639178a..3f76a407d7 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -190,6 +190,8 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		estate->es_param_exec_vals = (ParamExecData *)
 			palloc0(queryDesc->plannedstmt->nParamExec * sizeof(ParamExecData));
 
+	estate->es_sourceText = queryDesc->sourceText;
+
 	/*
 	 * If non-read-only query, set the command ID to mark output tuples with
 	 */
diff --git a/src/backend/executor/execParallel.c b/src/backend/executor/execParallel.c
index 646df087f9..de0e2bafe6 100644
--- a/src/backend/executor/execParallel.c
+++ b/src/backend/executor/execParallel.c
@@ -39,6 +39,7 @@
 #include "utils/dsa.h"
 #include "utils/memutils.h"
 #include "utils/snapmgr.h"
+#include "pgstat.h"
 
 /*
  * Magic numbers for parallel executor communication.  We use constants
@@ -51,6 +52,7 @@
 #define PARALLEL_KEY_TUPLE_QUEUE		UINT64CONST(0xE000000000000004)
 #define PARALLEL_KEY_INSTRUMENTATION	UINT64CONST(0xE000000000000005)
 #define PARALLEL_KEY_DSA				UINT64CONST(0xE000000000000006)
+#define PARALLEL_KEY_QUERY_TEXT		UINT64CONST(0xE000000000000007)
 
 #define PARALLEL_TUPLE_QUEUE_SIZE		65536
 
@@ -368,6 +370,8 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers)
 	int			instrumentation_len = 0;
 	int			instrument_offset = 0;
 	Size		dsa_minsize = dsa_minimum_size();
+	char	   *query_string;
+	int			query_len;
 
 	/* Allocate object for return value. */
 	pei = palloc0(sizeof(ParallelExecutorInfo));
@@ -387,6 +391,11 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers)
 	 * for the various things we need to store.
 	 */
 
+	/* Estimate space for query text. */
+	query_len = strlen(estate->es_sourceText);
+	shm_toc_estimate_chunk(&pcxt->estimator, query_len);
+	shm_toc_estimate_keys(&pcxt->estimator, 1);
+
 	/* Estimate space for serialized PlannedStmt. */
 	pstmt_len = strlen(pstmt_data) + 1;
 	shm_toc_estimate_chunk(&pcxt->estimator, pstmt_len);
@@ -451,6 +460,11 @@ ExecInitParallelPlan(PlanState *planstate, EState *estate, int nworkers)
 	 * asked for has been allocated or initialized yet, though, so do that.
 	 */
 
+	/* Store query string */
+	query_string = shm_toc_allocate(pcxt->toc, query_len);
+	memcpy(query_string, estate->es_sourceText, query_len);
+	shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, query_string);
+
 	/* Store serialized PlannedStmt. */
 	pstmt_space = shm_toc_allocate(pcxt->toc, pstmt_len);
 	memcpy(pstmt_space, pstmt_data, pstmt_len);
@@ -661,6 +675,10 @@ ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
 	char	   *paramspace;
 	PlannedStmt *pstmt;
 	ParamListInfo paramLI;
+	char	   *queryString;
+
+	/* Get the query string from shared memory */
+	queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT);
 
 	/* Reconstruct leader-supplied PlannedStmt. */
 	pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT);
@@ -679,7 +697,7 @@ ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
 	 * revising this someday.
 	 */
 	return CreateQueryDesc(pstmt,
-						   "<parallel query>",
+						   queryString,
 						   GetActiveSnapshot(), InvalidSnapshot,
 						   receiver, paramLI, instrument_options);
 }
@@ -799,6 +817,12 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
 		instrument_options = instrumentation->instrument_options;
 	queryDesc = ExecParallelGetQueryDesc(toc, receiver, instrument_options);
 
+	/* Setting debug_query_string for individual workers */
+	debug_query_string = queryDesc->sourceText;
+
+	/* Report workers' query for monitoring purposes */
+	pgstat_report_activity(STATE_RUNNING, debug_query_string);
+
 	/* Prepare to track buffer usage during query execution. */
 	InstrStartParallelQuery();
 
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index e49feff6c0..3d6a3801c0 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -139,6 +139,7 @@ CreateExecutorState(void)
 	estate->es_epqTuple = NULL;
 	estate->es_epqTupleSet = NULL;
 	estate->es_epqScanDone = NULL;
+	estate->es_sourceText = NULL;
 
 	/*
 	 * Return the executor state structure
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 1c1cb80a63..6332ea0620 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -371,6 +371,7 @@ typedef struct EState
 	Snapshot	es_crosscheck_snapshot; /* crosscheck time qual for RI */
 	List	   *es_range_table; /* List of RangeTblEntry */
 	PlannedStmt *es_plannedstmt;	/* link to top of plan tree */
+	const char *es_sourceText;	/* Source text from QueryDesc */
 
 	JunkFilter *es_junkFilter;	/* top-level junk filter, if any */