pgstat: Split out relation stats handling from AtEO[Sub]Xact_PgStat() etc.

An upcoming patch will add additional work to these functions. To avoid the
functions getting too complicated / doing too many things at once, split out
sub-tasks into their own functions.

Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20210405092914.mmxqe7j56lsjfsej@alap3.anarazel.de

src/backend/postmaster/pgstat.c

@@ -2374,43 +2374,19 @@ pgstat_update_heap_dead_tuples(Relation rel, int delta)
 		pgstat_info->t_counts.t_delta_dead_tuples -= delta;
 }
 
-
+/*
-/* ----------
+ * Perform relation stats specific end-of-transaction work. Helper for
- * AtEOXact_PgStat
+ * AtEOXact_PgStat.
  *
- *	Called from access/transam/xact.c at top-level transaction commit/abort.
+ * Transfer transactional insert/update counts into the base tabstat entries.
- * ----------
+ * We don't bother to free any of the transactional state, since it's all in
+ * TopTransactionContext and will go away anyway.
  */
-void
+static void
-AtEOXact_PgStat(bool isCommit, bool parallel)
+AtEOXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit)
 {
-	PgStat_SubXactStatus *xact_state;
-
-	/* Don't count parallel worker transaction stats */
-	if (!parallel)
-	{
-		/*
-		 * Count transaction commit or abort.  (We use counters, not just
-		 * bools, in case the reporting message isn't sent right away.)
-		 */
-		if (isCommit)
-			pgStatXactCommit++;
-		else
-			pgStatXactRollback++;
-	}
-
-	/*
-	 * Transfer transactional insert/update counts into the base tabstat
-	 * entries.  We don't bother to free any of the transactional state, since
-	 * it's all in TopTransactionContext and will go away anyway.
-	 */
-	xact_state = pgStatXactStack;
-	if (xact_state != NULL)
-	{
 	PgStat_TableXactStatus *trans;
 
-		Assert(xact_state->nest_level == 1);
-		Assert(xact_state->prev == NULL);
 	for (trans = xact_state->first; trans != NULL; trans = trans->next)
 	{
 		PgStat_TableStatus *tabstat;
@@ -2455,38 +2431,66 @@ AtEOXact_PgStat(bool isCommit, bool parallel)
 		}
 		tabstat->trans = NULL;
 	}
-	}
+}
-	pgStatXactStack = NULL;
 
-	/* Make sure any stats snapshot is thrown away */
+static void
-	pgstat_clear_snapshot();
+AtEOXact_PgStat_Database(bool isCommit, bool parallel)
+{
+	/* Don't count parallel worker transaction stats */
+	if (!parallel)
+	{
+		/*
+		 * Count transaction commit or abort.  (We use counters, not just
+		 * bools, in case the reporting message isn't sent right away.)
+		 */
+		if (isCommit)
+			pgStatXactCommit++;
+		else
+			pgStatXactRollback++;
+	}
 }
 
 /* ----------
- * AtEOSubXact_PgStat
+ * AtEOXact_PgStat
  *
- *	Called from access/transam/xact.c at subtransaction commit/abort.
+ *	Called from access/transam/xact.c at top-level transaction commit/abort.
  * ----------
  */
 void
-AtEOSubXact_PgStat(bool isCommit, int nestDepth)
+AtEOXact_PgStat(bool isCommit, bool parallel)
 {
 	PgStat_SubXactStatus *xact_state;
 
-	/*
+	AtEOXact_PgStat_Database(isCommit, parallel);
+
+	/* handle transactional stats information */
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL)
+	{
+		Assert(xact_state->nest_level == 1);
+		Assert(xact_state->prev == NULL);
+
+		AtEOXact_PgStat_Relations(xact_state, isCommit);
+	}
+	pgStatXactStack = NULL;
+
+	/* Make sure any stats snapshot is thrown away */
+	pgstat_clear_snapshot();
+}
+
+/*
+ * Perform relation stats specific end-of-sub-transaction work. Helper for
+ * AtEOSubXact_PgStat.
+ *
  * Transfer transactional insert/update counts into the next higher
  * subtransaction state.
  */
-	xact_state = pgStatXactStack;
+static void
-	if (xact_state != NULL &&
+AtEOSubXact_PgStat_Relations(PgStat_SubXactStatus *xact_state, bool isCommit, int nestDepth)
-		xact_state->nest_level >= nestDepth)
+{
-	{
 	PgStat_TableXactStatus *trans;
 	PgStat_TableXactStatus *next_trans;
 
-		/* delink xact_state from stack immediately to simplify reuse case */
-		pgStatXactStack = xact_state->prev;
-
 	for (trans = xact_state->first; trans != NULL; trans = next_trans)
 	{
 		PgStat_TableStatus *tabstat;
@@ -2495,6 +2499,7 @@ AtEOSubXact_PgStat(bool isCommit, int nestDepth)
 		Assert(trans->nest_level == nestDepth);
 		tabstat = trans->parent;
 		Assert(tabstat->trans == trans);
+
 		if (isCommit)
 		{
 			if (trans->upper && trans->upper->nest_level == nestDepth - 1)
@@ -2555,30 +2560,42 @@ AtEOSubXact_PgStat(bool isCommit, int nestDepth)
 			pfree(trans);
 		}
 	}
-		pfree(xact_state);
-	}
 }
 
-
+/* ----------
-/*
+ * AtEOSubXact_PgStat
- * AtPrepare_PgStat
- *		Save the transactional stats state at 2PC transaction prepare.
  *
- * In this phase we just generate 2PC records for all the pending
+ *	Called from access/transam/xact.c at subtransaction commit/abort.
- * transaction-dependent stats work.
+ * ----------
  */
 void
-AtPrepare_PgStat(void)
+AtEOSubXact_PgStat(bool isCommit, int nestDepth)
 {
 	PgStat_SubXactStatus *xact_state;
 
+	/* merge the sub-transaction's transactional stats into the parent */
 	xact_state = pgStatXactStack;
-	if (xact_state != NULL)
+	if (xact_state != NULL &&
+		xact_state->nest_level >= nestDepth)
 	{
+		/* delink xact_state from stack immediately to simplify reuse case */
+		pgStatXactStack = xact_state->prev;
+
+		AtEOSubXact_PgStat_Relations(xact_state, isCommit, nestDepth);
+
+		pfree(xact_state);
+	}
+}
+
+/*
+ * Generate 2PC records for all the pending transaction-dependent relation
+ * stats.
+ */
+static void
+AtPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state)
+{
 	PgStat_TableXactStatus *trans;
 
-		Assert(xact_state->nest_level == 1);
-		Assert(xact_state->prev == NULL);
 	for (trans = xact_state->first; trans != NULL; trans = trans->next)
 	{
 		PgStat_TableStatus *tabstat;
@@ -2602,6 +2619,46 @@ AtPrepare_PgStat(void)
 		RegisterTwoPhaseRecord(TWOPHASE_RM_PGSTAT_ID, 0,
 							   &record, sizeof(TwoPhasePgStatRecord));
 	}
+}
+
+/*
+ * AtPrepare_PgStat
+ *		Save the transactional stats state at 2PC transaction prepare.
+ */
+void
+AtPrepare_PgStat(void)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL)
+	{
+		Assert(xact_state->nest_level == 1);
+		Assert(xact_state->prev == NULL);
+
+		AtPrepare_PgStat_Relations(xact_state);
+	}
+}
+
+/*
+ * All we need do here is unlink the transaction stats state from the
+ * nontransactional state.  The nontransactional action counts will be
+ * reported to the stats collector immediately, while the effects on
+ * live and dead tuple counts are preserved in the 2PC state file.
+ *
+ * Note: AtEOXact_PgStat_Relations is not called during PREPARE.
+ */
+static void
+PostPrepare_PgStat_Relations(PgStat_SubXactStatus *xact_state)
+{
+	PgStat_TableXactStatus *trans;
+
+	for (trans = xact_state->first; trans != NULL; trans = trans->next)
+	{
+		PgStat_TableStatus *tabstat;
+
+		tabstat = trans->parent;
+		tabstat->trans = NULL;
 	}
 }
 
@@ -2609,11 +2666,6 @@ AtPrepare_PgStat(void)
  * PostPrepare_PgStat
  *		Clean up after successful PREPARE.
  *
- * All we need do here is unlink the transaction stats state from the
- * nontransactional state.  The nontransactional action counts will be
- * reported to the stats collector immediately, while the effects on live
- * and dead tuple counts are preserved in the 2PC state file.
- *
  * Note: AtEOXact_PgStat is not called during PREPARE.
  */
 void
@@ -2628,15 +2680,10 @@ PostPrepare_PgStat(void)
 	xact_state = pgStatXactStack;
 	if (xact_state != NULL)
 	{
-		PgStat_TableXactStatus *trans;
+		Assert(xact_state->nest_level == 1);
-
+		Assert(xact_state->prev == NULL);
-		for (trans = xact_state->first; trans != NULL; trans = trans->next)
-		{
-			PgStat_TableStatus *tabstat;
 
-			tabstat = trans->parent;
+		PostPrepare_PgStat_Relations(xact_state);
-			tabstat->trans = NULL;
-		}
 	}
 	pgStatXactStack = NULL;