MDEV-30544 Deprecate innodb_defragment and related parameters

There is a little used option innodb_defragment that would make
OPTIMIZE TABLE not rebuild the table as usual for InnoDB, but
instead cause the index B-trees to be optimized in place.

This option uses excessive locking (exclusively locking index trees).
It never covered SPATIAL INDEX or FULLTEXT INDEX. Storage space
was never reclaimed.

Because this option is not particularly useful and causes a
maintenance burden (most recently in
commit de4030e4),
it is best to deprecate it, to prepare for its removal.

mysql-test/main/lock_sync-master.opt

 --default-storage-engine=MyISAM
---innodb-defragment=0

mysql-test/suite/innodb/r/defrag_mdl-9155.result

 set global innodb_defragment=1;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 create table t1 (a int not null primary key auto_increment, b varchar(256), key second(a, b)) engine=innodb;
 insert t1 select null, repeat('a', 256) from seq_1_to_100;
 select count(*) from t1;
@@ -16,3 +18,5 @@ test.t1	optimize	status	OK
 connection con1;
 drop table t1;
 set global innodb_defragment=default;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release

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

@@ -3,6 +3,8 @@ SET @accuracy= @@GLOBAL.innodb_defragment_stats_accuracy;
 SET @sp= @@GLOBAL.innodb_stats_persistent;
 SET GLOBAL innodb_stats_persistent = 0;
 set global innodb_defragment_stats_accuracy = 80;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
 b VARCHAR(256),
 c INT,
@@ -18,6 +20,8 @@ connect  con3,localhost,root,,test,$MASTER_MYPORT,$MASTER_MYSOCK;
 connect  con4,localhost,root,,test,$MASTER_MYPORT,$MASTER_MYSOCK;
 connection default;
 SET @@global.innodb_defragment_n_pages = 20;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 CREATE TEMPORARY TABLE tt (a INT, KEY(a)) ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
 INSERT INTO tt SELECT 0 FROM seq_1_to_180;
 INSERT INTO tt SELECT 5 FROM seq_1_to_160;
@@ -98,5 +102,9 @@ count(stat_value) > 0
 1
 drop table t1;
 SET GLOBAL innodb_defragment_n_pages = @n_pages;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 SET GLOBAL innodb_defragment_stats_accuracy = @accuracy;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 SET GLOBAL innodb_stats_persistent = @sp;

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

 SET GLOBAL innodb_defragment_stats_accuracy = 20;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 DELETE FROM mysql.innodb_index_stats;
 # Create table.
 CREATE TABLE t1 (a INT PRIMARY KEY AUTO_INCREMENT, b VARCHAR(256),
@@ -77,6 +79,8 @@ t1	SECOND	n_leaf_pages_reserved
 t1	SECOND	n_page_split
 t1	SECOND	n_pages_freed
 set global innodb_defragment_stats_accuracy = 40;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 INSERT INTO t1 (b) SELECT b from t1;
 SELECT table_name, index_name, stat_name FROM mysql.innodb_index_stats;
 table_name	index_name	stat_name
@@ -116,6 +120,8 @@ drop index SECOND on t2;
 # MDEV-26636: Statistics must not be written for temporary tables
 #
 SET GLOBAL innodb_defragment_stats_accuracy = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 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;

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

@@ -5,6 +5,8 @@ SET @start_flush_log_at_trx_commit = @@global.innodb_flush_log_at_trx_commit;
 SET @@global.innodb_flush_log_at_trx_commit=2;
 SET @start_innodb_defragment_stats_accuracy = @@global.innodb_defragment_stats_accuracy;
 SET @@global.innodb_defragment_stats_accuracy = 80;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY AUTO_INCREMENT, b VARCHAR(256), KEY SECOND(a, b)) ENGINE=INNODB;
 INSERT INTO t1 VALUES(1, REPEAT('A', 256));
 INSERT INTO t1 (b) SELECT b from t1;
@@ -34,5 +36,7 @@ sleep(15)
 select stat_value > 0 from mysql.innodb_index_stats where table_name like '%t1%' and stat_name = 'n_page_split';
 stat_value > 0
 SET @@global.innodb_defragment_stats_accuracy = @start_innodb_defragment_stats_accuracy;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 SET @@global.table_definition_cache = @start_table_definition_cache;
 DROP TABLE t1;

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

 set global innodb_defragment_stats_accuracy = 80;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY AUTO_INCREMENT, b VARCHAR(256), KEY SECOND(a, b)) ENGINE=INNODB;
 optimize table t1;
 Table	Op	Msg_type	Msg_text
@@ -66,6 +68,8 @@ select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like
 count(stat_value) = 0
 1
 SET @@global.innodb_defragment_n_pages = 3;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 optimize table t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
@@ -104,6 +108,8 @@ select count(stat_value) = 0 from mysql.innodb_index_stats where table_name like
 count(stat_value) = 0
 1
 SET @@global.innodb_defragment_n_pages = 10;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 optimize table t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK

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

 SET @innodb_defragment_orig=@@GLOBAL.innodb_defragment;
 SET @innodb_optimize_fulltext_orig=@@GLOBAL.innodb_optimize_fulltext_only;
 SET GLOBAL innodb_defragment = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 SET GLOBAL innodb_optimize_fulltext_only = 0;
 #
 # MDEV-12198 innodb_defragment=1 crashes server on
@@ -27,6 +29,8 @@ OPTIMIZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
 SET GLOBAL innodb_defragment = 0;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 OPTIMIZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
@@ -37,4 +41,6 @@ Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
 DROP TABLE t1;
 SET GLOBAL innodb_defragment = @innodb_defragment_orig;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 SET GLOBAL innodb_optimize_fulltext_only = @innodb_optimize_fulltext_orig;

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

@@ -279,10 +279,14 @@ SET GLOBAL innodb_limit_optimistic_insert_debug = @old_limit;
 ALTER TABLE t1 ADD COLUMN b INT, ALGORITHM=INSTANT;
 SET @old_defragment = @@innodb_defragment;
 SET GLOBAL innodb_defragment = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 OPTIMIZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	optimize	status	OK
 SET GLOBAL innodb_defragment = @old_defragment;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 ALTER TABLE t1 ADD vb INT AS (b) VIRTUAL;
 CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text

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

---innodb-defragment=0
\ No newline at end of file

mysql-test/suite/sys_vars/r/innodb_defragment_basic.result

@@ -3,10 +3,14 @@ SELECT @orig;
 @orig
 0
 SET GLOBAL innodb_defragment = OFF;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment;
 @@global.innodb_defragment
 0
 SET GLOBAL innodb_defragment = ON;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment;
 @@global.innodb_defragment
 1
@@ -16,3 +20,5 @@ SELECT @@global.innodb_defragment;
 @@global.innodb_defragment
 1
 SET GLOBAL innodb_defragment = @orig;
+Warnings:
+Warning	1287	'@@innodb_defragment' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/innodb_defragment_fill_factor_basic.result

@@ -6,25 +6,33 @@ SELECT COUNT(@@global.innodb_defragment_fill_factor);
 COUNT(@@global.innodb_defragment_fill_factor)
 1
 SET @@global.innodb_defragment_fill_factor = 0.77777777777777;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
 0.777778
 SET @@global.innodb_defragment_fill_factor = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
 1.000000
 SET @@global.innodb_defragment_fill_factor = 0.7;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
 0.700000
 SET @@global.innodb_defragment_fill_factor = -1;
 Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_fill_factor value: '-1'
 SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
 0.700000
 SET @@global.innodb_defragment_fill_factor = 2;
 Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_fill_factor value: '2'
 SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
@@ -35,3 +43,5 @@ SELECT @@global.innodb_defragment_fill_factor;
 @@global.innodb_defragment_fill_factor
 1.000000
 SET @@global.innodb_defragment_fill_factor = @start_innodb_defragment_fill_factor;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/innodb_defragment_fill_factor_n_recs_basic.result

@@ -6,25 +6,33 @@ SELECT COUNT(@@global.innodb_defragment_fill_factor_n_recs);
 COUNT(@@global.innodb_defragment_fill_factor_n_recs)
 1
 SET @@global.innodb_defragment_fill_factor_n_recs = 50;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
 50
 SET @@global.innodb_defragment_fill_factor_n_recs = 100;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
 100
 SET @@global.innodb_defragment_fill_factor_n_recs = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
 1
 SET @@global.innodb_defragment_fill_factor_n_recs = -1;
 Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_fill_factor... value: '-1'
 SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
 1
 SET @@global.innodb_defragment_fill_factor_n_recs = 10000;
 Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_fill_factor... value: '10000'
 SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
@@ -40,3 +48,5 @@ SELECT @@global.innodb_defragment_fill_factor_n_recs;
 @@global.innodb_defragment_fill_factor_n_recs
 100
 SET @@global.innodb_defragment_fill_factor_n_recs = @start_innodb_defragment_fill_factor_n_recs;
+Warnings:
+Warning	1287	'@@innodb_defragment_fill_factor_n_recs' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/innodb_defragment_frequency_basic.result

@@ -6,25 +6,33 @@ SELECT COUNT(@@global.innodb_defragment_frequency);
 COUNT(@@global.innodb_defragment_frequency)
 1
 SET @@global.innodb_defragment_frequency = 200;
+Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
 200
 SET @@global.innodb_defragment_frequency = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
 1
 SET @@global.innodb_defragment_frequency = 1000;
+Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
 1000
 SET @@global.innodb_defragment_frequency = -1;
 Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_frequency value: '-1'
 SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
 1
 SET @@global.innodb_defragment_frequency = 10000;
 Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_frequency value: '10000'
 SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
@@ -40,3 +48,5 @@ SELECT @@global.innodb_defragment_frequency;
 @@global.innodb_defragment_frequency
 1000
 SET @@global.innodb_defragment_frequency = @start_innodb_defragment_frequency;
+Warnings:
+Warning	1287	'@@innodb_defragment_frequency' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/innodb_defragment_n_pages_basic.result

@@ -7,22 +7,30 @@ COUNT(@@global.innodb_defragment_n_pages)
 1
 SET @@global.innodb_defragment_n_pages = 1;
 Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_n_pages value: '1'
 SELECT @@global.innodb_defragment_n_pages;
 @@global.innodb_defragment_n_pages
 2
 SET @@global.innodb_defragment_n_pages = 2;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_n_pages;
 @@global.innodb_defragment_n_pages
 2
 SET @@global.innodb_defragment_n_pages = 32;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_n_pages;
 @@global.innodb_defragment_n_pages
 32
 SET @@global.innodb_defragment_n_pages = 64;
 Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_n_pages value: '64'
 SELECT @@global.innodb_defragment_n_pages;
 @@global.innodb_defragment_n_pages
 32
 SET @@global.innodb_defragment_n_pages = @start_innodb_defragment_n_pages;
+Warnings:
+Warning	1287	'@@innodb_defragment_n_pages' is deprecated and will be removed in a future release

mysql-test/suite/sys_vars/r/innodb_defragment_stats_accuracy_basic.result

@@ -6,21 +6,27 @@ SELECT COUNT(@@global.innodb_defragment_stats_accuracy);
 COUNT(@@global.innodb_defragment_stats_accuracy)
 1
 SET @@global.innodb_defragment_stats_accuracy = 1;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_stats_accuracy;
 @@global.innodb_defragment_stats_accuracy
 1
 SET @@global.innodb_defragment_stats_accuracy = 1000;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 SELECT @@global.innodb_defragment_stats_accuracy;
 @@global.innodb_defragment_stats_accuracy
 1000
 SET @@global.innodb_defragment_stats_accuracy = -1;
 Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_stats_accuracy value: '-1'
 SELECT @@global.innodb_defragment_stats_accuracy;
 @@global.innodb_defragment_stats_accuracy
 0
 SET @@global.innodb_defragment_stats_accuracy = 1000000000000;
 Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release
 Warning	1292	Truncated incorrect innodb_defragment_stats_accuracy value: '1000000000000'
 SELECT @@global.innodb_defragment_stats_accuracy;
 @@global.innodb_defragment_stats_accuracy
@@ -31,3 +37,5 @@ SELECT @@global.innodb_defragment_stats_accuracy;
 @@global.innodb_defragment_stats_accuracy
 4294967295
 SET @@global.innodb_defragment_stats_accuracy = @start_innodb_defragment_stats_accuracy;
+Warnings:
+Warning	1287	'@@innodb_defragment_stats_accuracy' is deprecated and will be removed in a future release

storage/innobase/handler/ha_innodb.cc

@@ -19092,7 +19092,7 @@ static MYSQL_SYSVAR_BOOL(buffer_pool_load_at_startup, srv_buffer_pool_load_at_st
   NULL, NULL, TRUE);
 
 static MYSQL_SYSVAR_BOOL(defragment, srv_defragment,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "Enable/disable InnoDB defragmentation (default FALSE). When set to FALSE, all existing "
   "defragmentation will be paused. And new defragmentation command will fail."
   "Paused defragmentation commands will resume when this variable is set to "
@@ -19100,14 +19100,14 @@ static MYSQL_SYSVAR_BOOL(defragment, srv_defragment,
   NULL, NULL, FALSE);
 
 static MYSQL_SYSVAR_UINT(defragment_n_pages, srv_defragment_n_pages,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "Number of pages considered at once when merging multiple pages to "
   "defragment",
   NULL, NULL, 7, 2, 32, 0);
 
 static MYSQL_SYSVAR_UINT(defragment_stats_accuracy,
   srv_defragment_stats_accuracy,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "How many defragment stats changes there are before the stats "
   "are written to persistent storage. Set to 0 meaning disable "
   "defragment stats tracking.",
@@ -19115,7 +19115,7 @@ static MYSQL_SYSVAR_UINT(defragment_stats_accuracy,
 
 static MYSQL_SYSVAR_UINT(defragment_fill_factor_n_recs,
   srv_defragment_fill_factor_n_recs,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "How many records of space defragmentation should leave on the page. "
   "This variable, together with innodb_defragment_fill_factor, is introduced "
   "so defragmentation won't pack the page too full and cause page split on "
@@ -19124,7 +19124,7 @@ static MYSQL_SYSVAR_UINT(defragment_fill_factor_n_recs,
   NULL, NULL, 20, 1, 100, 0);
 
 static MYSQL_SYSVAR_DOUBLE(defragment_fill_factor, srv_defragment_fill_factor,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "A number between [0.7, 1] that tells defragmentation how full it should "
   "fill a page. Default is 0.9. Number below 0.7 won't make much sense."
   "This variable, together with innodb_defragment_fill_factor_n_recs, is "
@@ -19134,7 +19134,7 @@ static MYSQL_SYSVAR_DOUBLE(defragment_fill_factor, srv_defragment_fill_factor,
   NULL, NULL, 0.9, 0.7, 1, 0);
 
 static MYSQL_SYSVAR_UINT(defragment_frequency, srv_defragment_frequency,
-  PLUGIN_VAR_RQCMDARG,
+  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_DEPRECATED,
   "Do not defragment a single index more than this number of time per second."
   "This controls the number of time defragmentation thread can request X_LOCK "
   "on an index. Defragmentation thread will check whether "