MDEV-15384 buf_flush_LRU_list_batch() always reports n->flushed=0, n->evicted=0

- buf_flush_LRU_list_batch() initializes the count to zero and updates them
correctly.

mysql-test/suite/innodb/r/purge_secondary.result

@@ -123,6 +123,10 @@ LENGTH(l)
 11197
 INSERT INTO t1 (a) SELECT NULL FROM t1;
 INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
 CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	status	OK
@@ -139,6 +143,18 @@ SELECT OTHER_INDEX_SIZE FROM INFORMATION_SCHEMA.INNODB_SYS_TABLESTATS
 WHERE NAME='test/t1';
 OTHER_INDEX_SIZE
 1
+SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
+WHERE NAME="buffer_LRU_batch_evict_total_pages" AND COUNT > 0;
+NAME	SUBSYSTEM
+buffer_LRU_batch_evict_total_pages	buffer
+SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
+WHERE NAME="buffer_LRU_batch_flush_total_pages" AND COUNT > 0;
+NAME	SUBSYSTEM
+buffer_LRU_batch_flush_total_pages	buffer
+SELECT (variable_value > 0) FROM information_schema.global_status
+WHERE LOWER(variable_name) LIKE 'INNODB_BUFFER_POOL_PAGES_FLUSHED';
+(variable_value > 0)
+1
 # Note: The OTHER_INDEX_SIZE does not cover any SPATIAL INDEX.
 # To test that all indexes were emptied, replace DROP TABLE
 # with the following, and examine the root pages in t1.ibd:

mysql-test/suite/innodb/t/purge_secondary.opt

@@ -1 +1,3 @@
 --innodb-sys-tablestats
+--innodb_buffer_pool_size=5M
+--innodb_monitor_enable=module_buffer

mysql-test/suite/innodb/t/purge_secondary.test

@@ -109,6 +109,10 @@ INSERT INTO t1 () VALUES (),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),();
 SELECT LENGTH(l) FROM t1;
 INSERT INTO t1 (a) SELECT NULL FROM t1;
 INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT NULL FROM t1;
 CHECK TABLE t1;
 UPDATE t1 SET c=true, l=ST_linefromtext('linestring(0 0,1 1,2 2)');
 DELETE FROM t1;
@@ -120,6 +124,15 @@ ANALYZE TABLE t1;
 SELECT OTHER_INDEX_SIZE FROM INFORMATION_SCHEMA.INNODB_SYS_TABLESTATS
 WHERE NAME='test/t1';
 
+SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
+WHERE NAME="buffer_LRU_batch_evict_total_pages" AND COUNT > 0;
+
+SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
+WHERE NAME="buffer_LRU_batch_flush_total_pages" AND COUNT > 0;
+
+SELECT (variable_value > 0) FROM information_schema.global_status
+WHERE LOWER(variable_name) LIKE 'INNODB_BUFFER_POOL_PAGES_FLUSHED';
+
 --echo # Note: The OTHER_INDEX_SIZE does not cover any SPATIAL INDEX.
 --echo # To test that all indexes were emptied, replace DROP TABLE
 --echo # with the following, and examine the root pages in t1.ibd:

storage/innobase/buf/buf0flu.cc

@@ -1631,8 +1631,6 @@ buf_flush_LRU_list_batch(
 {
 	buf_page_t*	bpage;
 	ulint		scanned = 0;
-	ulint		evict_count = 0;
-	ulint		count = 0;
 	ulint		free_len = UT_LIST_GET_LEN(buf_pool->free);
 	ulint		lru_len = UT_LIST_GET_LEN(buf_pool->LRU);
 	ulint		withdraw_depth = 0;
@@ -1648,7 +1646,7 @@ buf_flush_LRU_list_batch(
 	}
 
 	for (bpage = UT_LIST_GET_LAST(buf_pool->LRU);
-	     bpage != NULL && count + evict_count < max
+	     bpage != NULL && n->flushed + n->evicted < max
 	     && free_len < srv_LRU_scan_depth + withdraw_depth
 	     && lru_len > BUF_LRU_MIN_LEN;
 	     ++scanned,
@@ -1666,7 +1664,7 @@ buf_flush_LRU_list_batch(
 			clean and is not IO-fixed or buffer fixed. */
 			mutex_exit(block_mutex);
 			if (buf_LRU_free_page(bpage, true)) {
-				++evict_count;
+				++n->evicted;
 			}
 		} else if (buf_flush_ready_for_flush(bpage, BUF_FLUSH_LRU)) {
 			/* Block is ready for flush. Dispatch an IO
@@ -1674,7 +1672,7 @@ buf_flush_LRU_list_batch(
 			free list in IO completion routine. */
 			mutex_exit(block_mutex);
 			buf_flush_page_and_try_neighbors(
-				bpage, BUF_FLUSH_LRU, max, &count);
+				bpage, BUF_FLUSH_LRU, max, &n->flushed);
 		} else {
 			/* Can't evict or dispatch this block. Go to
 			previous. */
@@ -1698,12 +1696,12 @@ buf_flush_LRU_list_batch(
 
 	ut_ad(buf_pool_mutex_own(buf_pool));
 
-	if (evict_count) {
+	if (n->evicted) {
 		MONITOR_INC_VALUE_CUMULATIVE(
 			MONITOR_LRU_BATCH_EVICT_TOTAL_PAGE,
 			MONITOR_LRU_BATCH_EVICT_COUNT,
 			MONITOR_LRU_BATCH_EVICT_PAGES,
-			evict_count);
+			n->evicted);
 	}
 
 	if (scanned) {
@@ -2160,16 +2158,16 @@ buf_flush_lists(
 			failure. */
 			success = false;
 
-			continue;
 		}
+
+		n_flushed += n.flushed;
 	}
 
 	if (n_flushed) {
 		buf_flush_stats(n_flushed, 0);
-	}
+		if (n_processed) {
-
+			*n_processed = n_flushed;
-	if (n_processed) {
+		}
-		*n_processed = n_flushed;
 	}
 
 	return(success);