Commit ca5ca4b9 authored by unknown's avatar unknown

MWL#116: group commit

Implement binlog_optimize_thread_scheduling option to allow benchmarking the
effect of running commit_ordered() for multiple transactions all in one
thread.
parent a2d921be
CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=innodb;
INSERT INTO t1 VALUES (0);
SET DEBUG_SYNC= "commit_after_get_LOCK_log SIGNAL con1_waiting WAIT_FOR con3_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
INSERT INTO t1 VALUES (1);
SET DEBUG_SYNC= "now WAIT_FOR con1_waiting";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con2_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
INSERT INTO t1 VALUES (2);
SET DEBUG_SYNC= "now WAIT_FOR con2_queued";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con3_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
INSERT INTO t1 VALUES (3);
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
SET DEBUG_SYNC= "now SIGNAL con1_loop_cont";
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
SET DEBUG_SYNC= "now SIGNAL con1_loop_cont";
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
SELECT * FROM t1 ORDER BY a;
a
0
1
2
SET SESSION debug="+d,crash_dispatch_command_before";
SELECT 1;
Got one of the listed errors
Got one of the listed errors
SELECT * FROM t1 ORDER BY a;
a
0
1
2
3
InnoDB: Last MySQL binlog file position 0 767, file name ./master-bin.000001
SET DEBUG_SYNC= 'RESET';
DROP TABLE t1;
CREATE TABLE t1(a CHAR(255),
b CHAR(255),
c CHAR(255),
d CHAR(255),
id INT AUTO_INCREMENT,
PRIMARY KEY(id)) ENGINE=InnoDB;
create table t2 like t1;
create procedure setcrash(IN i INT)
begin
CASE i
WHEN 1 THEN SET SESSION debug="d,crash_commit_after_prepare";
WHEN 2 THEN SET SESSION debug="d,crash_commit_after_log";
WHEN 3 THEN SET SESSION debug="d,crash_commit_before_unlog";
WHEN 4 THEN SET SESSION debug="d,crash_commit_after";
WHEN 5 THEN SET SESSION debug="d,crash_commit_before";
ELSE BEGIN END;
END CASE;
end //
FLUSH TABLES;
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
call setcrash(5);
COMMIT;
Got one of the listed errors
SELECT * FROM t1 ORDER BY id;
a b c d id
SHOW BINLOG EVENTS LIMIT 2,1;
Log_name Pos Event_type Server_id End_log_pos Info
delete from t1;
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
call setcrash(4);
COMMIT;
Got one of the listed errors
SELECT * FROM t1 ORDER BY id;
a b c d id
a b c d 1
a b c d 2
a b c d 3
a b c d 4
a b c d 5
a b c d 6
a b c d 7
a b c d 8
a b c d 9
a b c d 10
SHOW BINLOG EVENTS LIMIT 2,1;
Log_name Pos Event_type Server_id End_log_pos Info
master-bin.000001 174 Query 1 268 use `test`; insert into t1 select * from t2
delete from t1;
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
call setcrash(3);
COMMIT;
Got one of the listed errors
SELECT * FROM t1 ORDER BY id;
a b c d id
a b c d 1
a b c d 2
a b c d 3
a b c d 4
a b c d 5
a b c d 6
a b c d 7
a b c d 8
a b c d 9
a b c d 10
SHOW BINLOG EVENTS LIMIT 2,1;
Log_name Pos Event_type Server_id End_log_pos Info
master-bin.000001 174 Query 1 268 use `test`; insert into t1 select * from t2
delete from t1;
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
call setcrash(2);
COMMIT;
Got one of the listed errors
SELECT * FROM t1 ORDER BY id;
a b c d id
a b c d 1
a b c d 2
a b c d 3
a b c d 4
a b c d 5
a b c d 6
a b c d 7
a b c d 8
a b c d 9
a b c d 10
SHOW BINLOG EVENTS LIMIT 2,1;
Log_name Pos Event_type Server_id End_log_pos Info
master-bin.000001 174 Query 1 268 use `test`; insert into t1 select * from t2
delete from t1;
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
call setcrash(1);
COMMIT;
Got one of the listed errors
SELECT * FROM t1 ORDER BY id;
a b c d id
SHOW BINLOG EVENTS LIMIT 2,1;
Log_name Pos Event_type Server_id End_log_pos Info
delete from t1;
DROP TABLE t1;
DROP TABLE t2;
DROP PROCEDURE setcrash;
CREATE TABLE t1 (a VARCHAR(10) PRIMARY KEY) ENGINE=innodb;
SELECT variable_value INTO @commits FROM information_schema.global_status
WHERE variable_name = 'binlog_commits';
SELECT variable_value INTO @group_commits FROM information_schema.global_status
WHERE variable_name = 'binlog_group_commits';
SET DEBUG_SYNC= "commit_before_get_LOCK_commit_ordered SIGNAL group1_running WAIT_FOR group2_queued";
INSERT INTO t1 VALUES ("con1");
set DEBUG_SYNC= "now WAIT_FOR group1_running";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con2";
SET DEBUG_SYNC= "commit_after_release_LOCK_log WAIT_FOR group3_committed";
INSERT INTO t1 VALUES ("con2");
SET DEBUG_SYNC= "now WAIT_FOR group2_con2";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con3";
INSERT INTO t1 VALUES ("con3");
SET DEBUG_SYNC= "now WAIT_FOR group2_con3";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con4";
SET DEBUG_SYNC= "commit_after_group_run_commit_ordered SIGNAL group2_visible WAIT_FOR group2_checked";
INSERT INTO t1 VALUES ("con4");
SET DEBUG_SYNC= "now WAIT_FOR group2_con4";
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
SELECT * FROM t1 ORDER BY a;
a
SET DEBUG_SYNC= "now SIGNAL group2_queued";
SELECT * FROM t1 ORDER BY a;
a
con1
SET DEBUG_SYNC= "commit_before_get_LOCK_commit_ordered SIGNAL group3_con5";
SET DEBUG_SYNC= "commit_after_get_LOCK_log SIGNAL con5_leader WAIT_FOR con6_queued";
INSERT INTO t1 VALUES ("con5");
SET DEBUG_SYNC= "now WAIT_FOR con5_leader";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con6_queued";
INSERT INTO t1 VALUES ("con6");
SET DEBUG_SYNC= "now WAIT_FOR group3_con5";
SELECT * FROM t1 ORDER BY a;
a
con1
SET DEBUG_SYNC= "now SIGNAL group3_committed";
SET DEBUG_SYNC= "now WAIT_FOR group2_visible";
SELECT * FROM t1 ORDER BY a;
a
con1
con2
con3
con4
SET DEBUG_SYNC= "now SIGNAL group2_checked";
SELECT * FROM t1 ORDER BY a;
a
con1
con2
con3
con4
con5
con6
SELECT variable_value - @commits FROM information_schema.global_status
WHERE variable_name = 'binlog_commits';
variable_value - @commits
6
SELECT variable_value - @group_commits FROM information_schema.global_status
WHERE variable_name = 'binlog_group_commits';
variable_value - @group_commits
3
SET DEBUG_SYNC= 'RESET';
DROP TABLE t1;
--binlog-optimize-thread-scheduling=0 --skip-stack-trace --skip-core-file
--source include/have_debug_sync.inc
--source include/have_innodb.inc
--source include/have_log_bin.inc
--source include/have_binlog_format_mixed_or_statement.inc
# Need DBUG to crash the server intentionally
--source include/have_debug.inc
# Don't test this under valgrind, memory leaks will occur as we crash
--source include/not_valgrind.inc
# XtraDB stores the binlog position corresponding to the last commit, and
# prints it during crash recovery.
# Test that we get the correct position when we group commit several
# transactions together.
CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=innodb;
INSERT INTO t1 VALUES (0);
connect(con1,localhost,root,,);
connect(con2,localhost,root,,);
connect(con3,localhost,root,,);
# Queue up three commits for group commit.
connection con1;
SET DEBUG_SYNC= "commit_after_get_LOCK_log SIGNAL con1_waiting WAIT_FOR con3_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
send INSERT INTO t1 VALUES (1);
connection con2;
SET DEBUG_SYNC= "now WAIT_FOR con1_waiting";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con2_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
send INSERT INTO t1 VALUES (2);
connection con3;
SET DEBUG_SYNC= "now WAIT_FOR con2_queued";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con3_queued";
SET DEBUG_SYNC= "commit_loop_entry_commit_ordered SIGNAL con1_loop WAIT_FOR con1_loop_cont";
send INSERT INTO t1 VALUES (3);
connection default;
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
# At this point, no transactions are committed.
SET DEBUG_SYNC= "now SIGNAL con1_loop_cont";
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
# At this point, 1 transaction is committed.
SET DEBUG_SYNC= "now SIGNAL con1_loop_cont";
SET DEBUG_SYNC= "now WAIT_FOR con1_loop";
# At this point, 2 transactions are committed.
SELECT * FROM t1 ORDER BY a;
connection con1;
reap;
connection con2;
reap;
# Now crash the server with 1+2 in-memory committed, 3 only prepared.
connection default;
system echo wait-group_commit_binlog_pos_no_optimize_thread.test >> $MYSQLTEST_VARDIR/tmp/mysqld.1.expect;
SET SESSION debug="+d,crash_dispatch_command_before";
--error 2006,2013
SELECT 1;
connection con3;
--error 2006,2013
reap;
system echo restart-group_commit_binlog_pos_no_optimize_thread.test >> $MYSQLTEST_VARDIR/tmp/mysqld.1.expect;
connection default;
--enable_reconnect
--source include/wait_until_connected_again.inc
# Crash recovery should recover all three transactions.
SELECT * FROM t1 ORDER BY a;
# Check that the binlog position reported by InnoDB is the correct one
# for the end of the second transaction (as can be checked with
# mysqlbinlog).
let $MYSQLD_DATADIR= `SELECT @@datadir`;
--exec grep 'InnoDB: Last MySQL binlog file position' $MYSQLD_DATADIR/../../log/mysqld.1.err | tail -1
SET DEBUG_SYNC= 'RESET';
DROP TABLE t1;
--binlog-optimize-thread-scheduling=0 --skip-stack-trace --skip-core-file
# Testing group commit by crashing a few times.
# Test adapted from the Facebook patch: lp:mysqlatfacebook
--source include/not_embedded.inc
# Don't test this under valgrind, memory leaks will occur
--source include/not_valgrind.inc
# Binary must be compiled with debug for crash to occur
--source include/have_debug.inc
--source include/have_innodb.inc
--source include/have_log_bin.inc
let $file_format_check=`SELECT @@innodb_file_format_check`;
CREATE TABLE t1(a CHAR(255),
b CHAR(255),
c CHAR(255),
d CHAR(255),
id INT AUTO_INCREMENT,
PRIMARY KEY(id)) ENGINE=InnoDB;
create table t2 like t1;
delimiter //;
create procedure setcrash(IN i INT)
begin
CASE i
WHEN 1 THEN SET SESSION debug="d,crash_commit_after_prepare";
WHEN 2 THEN SET SESSION debug="d,crash_commit_after_log";
WHEN 3 THEN SET SESSION debug="d,crash_commit_before_unlog";
WHEN 4 THEN SET SESSION debug="d,crash_commit_after";
WHEN 5 THEN SET SESSION debug="d,crash_commit_before";
ELSE BEGIN END;
END CASE;
end //
delimiter ;//
# Avoid getting a crashed mysql.proc table.
FLUSH TABLES;
let $numtests = 5;
let $numinserts = 10;
while ($numinserts)
{
dec $numinserts;
INSERT INTO t2(a, b, c, d) VALUES ('a', 'b', 'c', 'd');
}
--enable_reconnect
while ($numtests)
{
RESET MASTER;
START TRANSACTION;
insert into t1 select * from t2;
# Write file to make mysql-test-run.pl expect crash
--exec echo "restart" > $MYSQLTEST_VARDIR/tmp/mysqld.1.expect
eval call setcrash($numtests);
# Run the crashing query
--error 2006,2013
COMMIT;
# Poll the server waiting for it to be back online again.
--source include/wait_until_connected_again.inc
# table and binlog should be in sync.
SELECT * FROM t1 ORDER BY id;
SHOW BINLOG EVENTS LIMIT 2,1;
delete from t1;
dec $numtests;
}
# final cleanup
DROP TABLE t1;
DROP TABLE t2;
DROP PROCEDURE setcrash;
--disable_query_log
eval SET GLOBAL innodb_file_format_check=$file_format_check;
--enable_query_log
--source include/have_debug_sync.inc
--source include/have_innodb.inc
--source include/have_log_bin.inc
# Test some group commit code paths by using debug_sync to do controlled
# commits of 6 transactions: first 1 alone, then 3 as a group, then 2 as a
# group.
#
# Group 3 is allowed to race as far as possible ahead before group 2 finishes
# to check some edge case for concurrency control.
CREATE TABLE t1 (a VARCHAR(10) PRIMARY KEY) ENGINE=innodb;
SELECT variable_value INTO @commits FROM information_schema.global_status
WHERE variable_name = 'binlog_commits';
SELECT variable_value INTO @group_commits FROM information_schema.global_status
WHERE variable_name = 'binlog_group_commits';
connect(con1,localhost,root,,);
connect(con2,localhost,root,,);
connect(con3,localhost,root,,);
connect(con4,localhost,root,,);
connect(con5,localhost,root,,);
connect(con6,localhost,root,,);
# Start group1 (with one thread) doing commit, waiting for
# group2 to queue up before finishing.
connection con1;
SET DEBUG_SYNC= "commit_before_get_LOCK_commit_ordered SIGNAL group1_running WAIT_FOR group2_queued";
send INSERT INTO t1 VALUES ("con1");
# Make group2 (with three threads) queue up.
# Make sure con2 is the group commit leader for group2.
# Make group2 wait with running commit_ordered() until group3 has committed.
connection con2;
set DEBUG_SYNC= "now WAIT_FOR group1_running";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con2";
SET DEBUG_SYNC= "commit_after_release_LOCK_log WAIT_FOR group3_committed";
send INSERT INTO t1 VALUES ("con2");
connection con3;
SET DEBUG_SYNC= "now WAIT_FOR group2_con2";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con3";
send INSERT INTO t1 VALUES ("con3");
connection con4;
SET DEBUG_SYNC= "now WAIT_FOR group2_con3";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL group2_con4";
SET DEBUG_SYNC= "commit_after_group_run_commit_ordered SIGNAL group2_visible WAIT_FOR group2_checked";
send INSERT INTO t1 VALUES ("con4");
# When group2 is queued, let group1 continue and queue group3.
connection default;
SET DEBUG_SYNC= "now WAIT_FOR group2_con4";
# At this point, trasaction 1 is still not visible as commit_ordered() has not
# been called yet.
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;
SELECT * FROM t1 ORDER BY a;
SET DEBUG_SYNC= "now SIGNAL group2_queued";
connection con1;
reap;
# Now transaction 1 is visible.
connection default;
SELECT * FROM t1 ORDER BY a;
connection con5;
SET DEBUG_SYNC= "commit_before_get_LOCK_commit_ordered SIGNAL group3_con5";
SET DEBUG_SYNC= "commit_after_get_LOCK_log SIGNAL con5_leader WAIT_FOR con6_queued";
send INSERT INTO t1 VALUES ("con5");
connection con6;
SET DEBUG_SYNC= "now WAIT_FOR con5_leader";
SET DEBUG_SYNC= "commit_after_prepare_ordered SIGNAL con6_queued";
send INSERT INTO t1 VALUES ("con6");
connection default;
SET DEBUG_SYNC= "now WAIT_FOR group3_con5";
# Still only transaction 1 visible, as group2 have not yet run commit_ordered().
SELECT * FROM t1 ORDER BY a;
SET DEBUG_SYNC= "now SIGNAL group3_committed";
SET DEBUG_SYNC= "now WAIT_FOR group2_visible";
# Now transactions 1-4 visible.
SELECT * FROM t1 ORDER BY a;
SET DEBUG_SYNC= "now SIGNAL group2_checked";
connection con2;
reap;
connection con3;
reap;
connection con4;
reap;
connection con5;
reap;
connection con6;
reap;
connection default;
# Check all transactions finally visible.
SELECT * FROM t1 ORDER BY a;
SELECT variable_value - @commits FROM information_schema.global_status
WHERE variable_name = 'binlog_commits';
SELECT variable_value - @group_commits FROM information_schema.global_status
WHERE variable_name = 'binlog_group_commits';
SET DEBUG_SYNC= 'RESET';
DROP TABLE t1;
......@@ -2510,7 +2510,8 @@ const char *MYSQL_LOG::generate_name(const char *log_name,
MYSQL_BIN_LOG::MYSQL_BIN_LOG()
:bytes_written(0), prepared_xids(0), file_id(1), open_count(1),
need_start_event(TRUE),
group_commit_queue(0), num_commits(0), num_group_commits(0),
group_commit_queue(0), group_commit_queue_busy(FALSE),
num_commits(0), num_group_commits(0),
is_relay_log(0),
description_event_for_exec(0), description_event_for_queue(0)
{
......@@ -2567,6 +2568,7 @@ void MYSQL_BIN_LOG::init_pthread_objects()
(void) my_pthread_mutex_init(&LOCK_index, MY_MUTEX_INIT_SLOW, "LOCK_index",
MYF_NO_DEADLOCK_DETECTION);
(void) pthread_cond_init(&update_cond, 0);
(void) pthread_cond_init(&COND_queue_busy, 0);
}
......@@ -3989,6 +3991,7 @@ err:
}
static my_bool opt_optimize_thread_scheduling= TRUE;
#ifndef DBUG_OFF
static ulong opt_binlog_dbug_fsync_sleep= 0;
#endif
......@@ -4925,6 +4928,32 @@ MYSQL_BIN_LOG::write_transaction_to_binlog_events(group_commit_entry *entry)
else
trx_group_commit_leader(entry);
if (!opt_optimize_thread_scheduling)
{
/* For the leader, trx_group_commit_leader() already took the lock. */
if (orig_queue != NULL)
pthread_mutex_lock(&LOCK_commit_ordered);
DEBUG_SYNC(entry->thd, "commit_loop_entry_commit_ordered");
++num_commits;
if (entry->trx_data->using_xa && !entry->error)
run_commit_ordered(entry->thd, entry->all);
group_commit_entry *next= entry->next;
if (!next)
{
group_commit_queue_busy= FALSE;
pthread_cond_signal(&COND_queue_busy);
DEBUG_SYNC(entry->thd, "commit_after_group_run_commit_ordered");
}
pthread_mutex_unlock(&LOCK_commit_ordered);
if (next)
{
next->thd->signal_wakeup_ready();
}
}
if (!entry->error)
return 0;
......@@ -5088,6 +5117,24 @@ MYSQL_BIN_LOG::trx_group_commit_leader(group_commit_entry *leader)
DEBUG_SYNC(leader->thd, "commit_after_release_LOCK_log");
++num_group_commits;
if (!opt_optimize_thread_scheduling)
{
/*
If we want to run commit_ordered() each in the transaction's own thread
context, then we need to mark the queue reserved; we need to finish all
threads in one group commit before the next group commit can be allowed
to proceed, and we cannot unlock a simple pthreads mutex in a different
thread from the one that locked it.
*/
while (group_commit_queue_busy)
pthread_cond_wait(&COND_queue_busy, &LOCK_commit_ordered);
group_commit_queue_busy= TRUE;
/* Note that we return with LOCK_commit_ordered locked! */
DBUG_VOID_RETURN;
}
/*
Wakeup each participant waiting for our group commit, first calling the
commit_ordered() methods for any transactions doing 2-phase commit.
......@@ -6578,6 +6625,16 @@ static SHOW_VAR binlog_status_vars_top[]= {
{NullS, NullS, SHOW_LONG}
};
static MYSQL_SYSVAR_BOOL(
optimize_thread_scheduling,
opt_optimize_thread_scheduling,
PLUGIN_VAR_READONLY,
"Run fast part of group commit in a single thread, to optimize kernel\n"
"thread scheduling",
NULL,
NULL,
1);
#ifndef DBUG_OFF
static MYSQL_SYSVAR_ULONG(
dbug_fsync_sleep,
......@@ -6590,13 +6647,16 @@ static MYSQL_SYSVAR_ULONG(
0,
ULONG_MAX,
0);
#endif
static struct st_mysql_sys_var *binlog_sys_vars[]=
{
MYSQL_SYSVAR(optimize_thread_scheduling),
#ifndef DBUG_OFF
MYSQL_SYSVAR(dbug_fsync_sleep),
#endif
NULL
};
#endif
/*
......@@ -6634,11 +6694,7 @@ mysql_declare_plugin(binlog)
NULL, /* Plugin Deinit */
0x0100 /* 1.0 */,
binlog_status_vars_top, /* status variables */
#ifndef DBUG_OFF
binlog_sys_vars, /* system variables */
#else
NULL, /* system variables */
#endif
NULL /* config options */
}
mysql_declare_plugin_end;
......@@ -370,6 +370,14 @@ class MYSQL_BIN_LOG: public TC_LOG, private MYSQL_LOG
bool no_auto_events;
/* Queue of transactions queued up to participate in group commit. */
group_commit_entry *group_commit_queue;
/*
Condition variable to mark that the group commit queue is busy.
Used when each thread does it's own commit_ordered() (when
binlog_optimize_thread_scheduling=1).
Used with the LOCK_commit_ordered mutex.
*/
my_bool group_commit_queue_busy;
pthread_cond_t COND_queue_busy;
/* Total number of committed transactions. */
ulonglong num_commits;
/* Number of group commits done. */
......
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