MDEV-18878: Slimmer purge in non-debug builds

purge_node_t::in_progress: Replaces purge_node_t::done.
Only present in debug builds.

purge_node_t::start(): Moved from the start of row_purge_step().

purge_node_t::end(): Replaces row_purge_end().

trx_purge_attach_undo_recs(): Omit a check from non-debug builds.

storage/innobase/include/row0purge.h

@@ -115,13 +115,16 @@ struct purge_node_t{
 	mem_heap_t*	heap;	/*!< memory heap used as auxiliary storage for
 				row; this must be emptied after a successful
 				purge of a row */
-	ibool		found_clust;/* TRUE if the clustered index record
+	ibool		found_clust;/*!< whether the clustered index record
 				determined by ref was found in the clustered
 				index, and we were able to position pcur on
 				it */
 	btr_pcur_t	pcur;	/*!< persistent cursor used in searching the
 				clustered index record */
-	ibool		done;	/* Debug flag */
+#ifdef UNIV_DEBUG
+	/** whether the operation is in progress */
+	bool		in_progress;
+#endif
 	trx_id_t	trx_id;	/*!< trx id for this purging record */
 
 	/** Virtual column information about opening of MariaDB table.
@@ -130,8 +133,7 @@ struct purge_node_t{
 
 	/** Constructor */
 	explicit purge_node_t(que_thr_t* parent) :
-		common(QUE_NODE_PURGE, parent), heap(mem_heap_create(256)),
-		done(TRUE)
+		common(QUE_NODE_PURGE, parent), heap(mem_heap_create(256))
 	{}
 
 #ifdef UNIV_DEBUG
@@ -167,6 +169,34 @@ struct purge_node_t{
 		unavailable_table_id = id;
 		def_trx_id = limit;
 	}
+
+	/** Start processing an undo log record. */
+	void start()
+	{
+		ut_ad(in_progress);
+		DBUG_ASSERT(common.type == QUE_NODE_PURGE);
+
+		table = NULL;
+		row = NULL;
+		ref = NULL;
+		index = NULL;
+		update = NULL;
+		found_clust = FALSE;
+		rec_type = ULINT_UNDEFINED;
+		cmpl_info = ULINT_UNDEFINED;
+	}
+
+	/** Reset the state at end
+	@return the query graph parent */
+	que_node_t* end()
+	{
+		DBUG_ASSERT(common.type == QUE_NODE_PURGE);
+		undo_recs = NULL;
+		ut_d(in_progress = false);
+		vcol_info.reset();
+		mem_heap_empty(heap);
+		return common.parent;
+	}
 };
 
 #endif

storage/innobase/row/row0purge.cc

@@ -1176,25 +1176,11 @@ row_purge_end(
 /*==========*/
 	que_thr_t*	thr)	/*!< in: query thread */
 {
-	purge_node_t*	node;
-
 	ut_ad(thr);
 
-	node = static_cast<purge_node_t*>(thr->run_node);
-
-	ut_ad(que_node_get_type(node) == QUE_NODE_PURGE);
-
-	thr->run_node = que_node_get_parent(node);
-
-	node->undo_recs = NULL;
-
-	node->done = TRUE;
-
-	node->vcol_info.reset();
+	thr->run_node = static_cast<purge_node_t*>(thr->run_node)->end();
 
 	ut_a(thr->run_node != NULL);
-
-	mem_heap_empty(node->heap);
 }
 
 /***********************************************************//**
@@ -1212,18 +1198,7 @@ row_purge_step(
 
 	node = static_cast<purge_node_t*>(thr->run_node);
 
-	node->table = NULL;
-	node->row = NULL;
-	node->ref = NULL;
-	node->index = NULL;
-	node->update = NULL;
-	node->found_clust = FALSE;
-	node->rec_type = ULINT_UNDEFINED;
-	node->cmpl_info = ULINT_UNDEFINED;
-
-	ut_a(!node->done);
-
-	ut_ad(que_node_get_type(node) == QUE_NODE_PURGE);
+	node->start();
 
 	if (!(node->undo_recs == NULL || ib_vector_is_empty(node->undo_recs))) {
 		trx_purge_rec_t*purge_rec;

storage/innobase/trx/trx0purge.cc

@@ -1501,14 +1501,16 @@ trx_purge_attach_undo_recs(
 	ulint		batch_size)	/*!< in: no. of pages to purge */
 {
 	que_thr_t*	thr;
-	ulint		i = 0;
+	ulint		i;
 	ulint		n_pages_handled = 0;
 	ulint		n_thrs = UT_LIST_GET_LEN(purge_sys->query->thrs);
 
 	ut_a(n_purge_threads > 0);
 
 	purge_sys->limit = purge_sys->iter;
 
+#ifdef UNIV_DEBUG
+	i = 0;
 	/* Debug code to validate some pre-requisites and reset done flag. */
 	for (thr = UT_LIST_GET_FIRST(purge_sys->query->thrs);
 	     thr != NULL && i < n_purge_threads;
@@ -1519,16 +1521,16 @@ trx_purge_attach_undo_recs(
 		/* Get the purge node. */
 		node = (purge_node_t*) thr->child;
 
-		ut_a(que_node_get_type(node) == QUE_NODE_PURGE);
-		ut_a(node->undo_recs == NULL);
-		ut_a(node->done);
-
-		node->done = FALSE;
+		ut_ad(que_node_get_type(node) == QUE_NODE_PURGE);
+		ut_ad(node->undo_recs == NULL);
+		ut_ad(!node->in_progress);
+		ut_d(node->in_progress = true);
 	}
 
 	/* There should never be fewer nodes than threads, the inverse
 	however is allowed because we only use purge threads as needed. */
-	ut_a(i == n_purge_threads);
+	ut_ad(i == n_purge_threads);
+#endif
 
 	/* Fetch and parse the UNDO records. The UNDO records are added
 	to a per purge node vector. */