MDEV-26636: InnoDB defragmentation statistics cause races on TEMPORARY TABLE

btr_defragment_save_defrag_stats_if_needed(): Do not save
defragmentation statistics for temporary tables.
They are exempt of defragmentation anyway
(ha_innobase::optimize() never invokes defragmentation for them),
and the user-visible names are not available inside InnoDB.

Furthermore, InnoDB assumes that temporary tables are never accessed
by other threads than the one that handles the session with which
the temporary table is associated with.

Furthermore, we simplify the test innodb.innodb_defrag_stats
and include a test case that demonstrates that defragmentation
statistics are no longer being saved for temporary tables.

3 files changed, 62 insertions, 116 deletions

diff --git a/mysql-test/suite/innodb/r/innodb_defrag_stats.result b/mysql-test/suite/innodb/r/innodb_defrag_stats.result
index 7092688f07b..6c5fe1817e2 100644
--- a/mysql-test/suite/innodb/r/innodb_defrag_stats.result
+++ b/mysql-test/suite/innodb/r/innodb_defrag_stats.result
@@ -1,22 +1,8 @@
-DROP TABLE if exists t1;
-select @@global.innodb_stats_persistent;
-@@global.innodb_stats_persistent
-0
-set global innodb_defragment_stats_accuracy = 20;
+SET GLOBAL innodb_defragment_stats_accuracy = 20;
+DELETE FROM mysql.innodb_index_stats;
 # Create table.
 CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY AUTO_INCREMENT, b VARCHAR(256), KEY SECOND(a, b)) ENGINE=INNODB;
-# Populate data
-INSERT INTO t1 VALUES(1, REPEAT('A', 256));
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
+INSERT INTO t1 SELECT seq, REPEAT('A', 256) FROM seq_1_to_1024;
 # Not enough page splits to trigger persistent stats write yet.
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 count(stat_value) = 0
@@ -27,7 +13,7 @@ count(stat_value) = 0
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
 count(stat_value) = 0
 1
-INSERT INTO t1 (b) SELECT b from t1;
+INSERT INTO t1 SELECT seq, REPEAT('A', 256) FROM seq_1025_to_2048;
 # Persistent stats recorded.
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 count(stat_value) > 0
@@ -39,6 +25,7 @@ select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like
 count(stat_value) > 0
 1
 # Delete some rows.
+BEGIN;
 delete from t1 where a between 100 * 20 and 100 * 20 + 30;
 delete from t1 where a between 100 * 19 and 100 * 19 + 30;
 delete from t1 where a between 100 * 18 and 100 * 18 + 30;
@@ -59,8 +46,7 @@ delete from t1 where a between 100 * 4 and 100 * 4 + 30;
 delete from t1 where a between 100 * 3 and 100 * 3 + 30;
 delete from t1 where a between 100 * 2 and 100 * 2 + 30;
 delete from t1 where a between 100 * 1 and 100 * 1 + 30;
-# Server Restarted
-# Confirm persistent stats still there after restart.
+COMMIT;
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 count(stat_value) > 0
 1
@@ -73,9 +59,6 @@ count(stat_value) > 0
 optimize table t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
-select sleep(2);
-sleep(2)
-0
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 count(stat_value) > 0
 1
@@ -108,9 +91,6 @@ count(stat_value) > 0
 1
 # Table rename should cause stats rename.
 rename table t1 to t2;
-select sleep(1);
-sleep(1)
-0
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 count(stat_value) = 0
 1
@@ -129,47 +109,36 @@ count(stat_value) > 0
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
 count(stat_value) > 0
 1
-# Drop index should cause stats drop.
+# Drop index should cause stats drop, but will not.
 drop index SECOND on t2;
-select sleep(3);
-sleep(3)
-0
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and  stat_name in ('n_page_split');
-count(stat_value) > 0
-1
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and  stat_name in ('n_pages_freed');
-count(stat_value) > 0
-1
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and stat_name in ('n_leaf_pages_defrag');
-count(stat_value) > 0
-1
-Server Restarted
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
-count(stat_value) = 0
-1
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
-count(stat_value) = 0
-1
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
-count(stat_value) = 0
-1
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_page_split');
-count(stat_value) > 0
-1
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_pages_freed');
-count(stat_value) > 0
-1
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
-count(stat_value) > 0
-1
+SELECT stat_name, stat_value>0 FROM mysql.innodb_index_stats
+WHERE table_name like '%t2%' AND index_name='SECOND';
+stat_name	stat_value>0
+n_leaf_pages_defrag	1
+n_leaf_pages_reserved	1
+n_page_split	1
+n_pages_freed	1
+#
+# MDEV-26636: Statistics must not be written for temporary tables
+#
+SET GLOBAL innodb_defragment_stats_accuracy = 1;
+CREATE TEMPORARY TABLE t (a INT PRIMARY KEY, c CHAR(255) NOT NULL)
+ENGINE=InnoDB;
+INSERT INTO t SELECT seq, '' FROM seq_1_to_100;
+SELECT * FROM mysql.innodb_index_stats where table_name like '%t1%';
+database_name	table_name	index_name	last_update	stat_name	stat_value	sample_size	stat_description
+SELECT table_name, index_name, stat_name, stat_value>0
+FROM mysql.innodb_index_stats;
+table_name	index_name	stat_name	stat_value>0
+t2	PRIMARY	n_leaf_pages_defrag	1
+t2	PRIMARY	n_leaf_pages_reserved	1
+t2	PRIMARY	n_page_split	1
+t2	PRIMARY	n_pages_freed	1
+t2	SECOND	n_leaf_pages_defrag	1
+t2	SECOND	n_leaf_pages_reserved	1
+t2	SECOND	n_page_split	1
+t2	SECOND	n_pages_freed	1
 # Clean up
 DROP TABLE t2;
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_page_split');
-count(stat_value) = 0
-1
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_pages_freed');
-count(stat_value) = 0
-1
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
-count(stat_value) = 0
-1
+SELECT * FROM mysql.innodb_index_stats;
+database_name	table_name	index_name	last_update	stat_name	stat_value	sample_size	stat_description
diff --git a/mysql-test/suite/innodb/t/innodb_defrag_stats.test b/mysql-test/suite/innodb/t/innodb_defrag_stats.test
index 2a5026a68e5..e1e88a07477 100644
--- a/mysql-test/suite/innodb/t/innodb_defrag_stats.test
+++ b/mysql-test/suite/innodb/t/innodb_defrag_stats.test
@@ -1,41 +1,23 @@
 --source include/have_innodb.inc
---source include/big_test.inc
 --source include/not_valgrind.inc
 --source include/not_embedded.inc
+--source include/have_sequence.inc
 
---disable_warnings
-DROP TABLE if exists t1;
---enable_warnings
+SET GLOBAL innodb_defragment_stats_accuracy = 20;
 
---disable_query_log
-let $innodb_defragment_stats_accuracy_orig=`select @@innodb_defragment_stats_accuracy`;
---enable_query_log
-
-select @@global.innodb_stats_persistent;
-set global innodb_defragment_stats_accuracy = 20;
+DELETE FROM mysql.innodb_index_stats;
 
 --echo # Create table.
 CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY AUTO_INCREMENT, b VARCHAR(256), KEY SECOND(a, b)) ENGINE=INNODB;
 
---echo # Populate data
-INSERT INTO t1 VALUES(1, REPEAT('A', 256));
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
-INSERT INTO t1 (b) SELECT b from t1;
+INSERT INTO t1 SELECT seq, REPEAT('A', 256) FROM seq_1_to_1024;
 
 --echo # Not enough page splits to trigger persistent stats write yet.
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
 
-INSERT INTO t1 (b) SELECT b from t1;
+INSERT INTO t1 SELECT seq, REPEAT('A', 256) FROM seq_1025_to_2048;
 
 --echo # Persistent stats recorded.
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
@@ -43,6 +25,7 @@ select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
 
 --echo # Delete some rows.
+BEGIN;
 let $num_delete = 20;
 while ($num_delete)
 {
@@ -50,17 +33,13 @@ while ($num_delete)
     eval delete from t1 where a between $j and $j + 30;
     dec $num_delete;
 }
+COMMIT;
 
---source include/restart_mysqld.inc
---echo # Server Restarted
-
---echo # Confirm persistent stats still there after restart.
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
 
 optimize table t1;
-select sleep(2);
 
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
@@ -84,7 +63,6 @@ select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like
 
 --echo # Table rename should cause stats rename.
 rename table t1 to t2;
-select sleep(1);
 
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
 select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
@@ -94,32 +72,30 @@ select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_pages_freed');
 select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
 
---echo # Drop index should cause stats drop.
+--echo # Drop index should cause stats drop, but will not.
 drop index SECOND on t2;
-select sleep(3);
 
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and  stat_name in ('n_page_split');
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and  stat_name in ('n_pages_freed');
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and index_name = 'SECOND' and stat_name in ('n_leaf_pages_defrag');
+--sorted_result
+SELECT stat_name, stat_value>0 FROM mysql.innodb_index_stats
+WHERE table_name like '%t2%' AND index_name='SECOND';
+
+--echo #
+--echo # MDEV-26636: Statistics must not be written for temporary tables
+--echo #
+SET GLOBAL innodb_defragment_stats_accuracy = 1;
+CREATE TEMPORARY TABLE t (a INT PRIMARY KEY, c CHAR(255) NOT NULL)
+ENGINE=InnoDB;
+INSERT INTO t SELECT seq, '' FROM seq_1_to_100;
 
 --source include/restart_mysqld.inc
---echo Server Restarted
 
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_page_split');
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_pages_freed');
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t1%' and  stat_name in ('n_leaf_pages_defrag');
+SELECT * FROM mysql.innodb_index_stats where table_name like '%t1%';
 
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_page_split');
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_pages_freed');
-select count(stat_value) > 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
+--sorted_result
+SELECT table_name, index_name, stat_name, stat_value>0
+FROM mysql.innodb_index_stats;
 
 --echo # Clean up
 DROP TABLE t2;
 
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_page_split');
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_pages_freed');
-select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like '%t2%' and  stat_name in ('n_leaf_pages_defrag');
-
---disable_query_log
-EVAL SET GLOBAL innodb_defragment_stats_accuracy = $innodb_defragment_stats_accuracy_orig;
---enable_query_log
+SELECT * FROM mysql.innodb_index_stats;
diff --git a/storage/innobase/btr/btr0defragment.cc b/storage/innobase/btr/btr0defragment.cc
index 38ef1db9cec..36dd9ab8470 100644
--- a/storage/innobase/btr/btr0defragment.cc
+++ b/storage/innobase/btr/btr0defragment.cc
@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (C) 2012, 2014 Facebook, Inc. All Rights Reserved.
-Copyright (C) 2014, 2019, MariaDB Corporation.
+Copyright (C) 2014, 2021, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -312,6 +312,7 @@ btr_defragment_save_defrag_stats_if_needed(
 {
 	if (srv_defragment_stats_accuracy != 0 // stats tracking disabled
 	    && dict_index_get_space(index) != 0 // do not track system tables
+	    && !index->table->is_temporary()
 	    && index->stat_defrag_modified_counter
 	       >= srv_defragment_stats_accuracy) {
 		dict_stats_defrag_pool_add(index);