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mysqld --debug-sync

2016-07-06 00:01 309 查看

http://hedengcheng.com/?p=238 https://dev.mysql.com/doc/internals/en/debug-sync-facility.html 
mysqld --datadir=/data --basedir=/usr/local/mysql56 --user=mysql --gdb  --debug-sync

会话1:

SET DEBUG_SYNC= 'RESET';

SET DEBUG_SYNC= 'before_lock_tables_takes_lock SIGNAL opened WAIT_FOR flushed';

mysql> insert into t2 select 1;     卡住

窗口2，GDB 调试mysqld进程，查看用户线程状态

GDB：

Thread 2 (Thread 0x7f7c2f1fe940 (LWP 16108)):
#0  0x00007f7c989cd280 in pthread_cond_timedwait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
#1  0x0000000000abe163 in safe_cond_timedwait (cond=0x17ecd70 <debug_sync_global+48>, mp=0x17ecda8 <debug_sync_global+104>, abstime=0x7f7c2f1fbc00, file=0xee85d8 "/usr/src/mysql-5.6.28/include/mysql/psi/mysql_thread.h", line=1199) at /usr/src/mysql-5.6.28/mysys/thr_mutex.c:278
#2  0x0000000000613ada in inline_mysql_cond_timedwait (that=0x17ecd70 <debug_sync_global+48>, mutex=0x17ecda8 <debug_sync_global+104>, abstime=0x7f7c2f1fbc00, src_file=0xee81c8 "/usr/src/mysql-5.6.28/sql/debug_sync.cc", src_line=1863) at /usr/src/mysql-5.6.28/include/mysql/psi/mysql_thread.h:1199
#3  0x00000000006141aa in debug_sync_execute (thd=0x48f3f20, action=0x4a9d780) at /usr/src/mysql-5.6.28/sql/debug_sync.cc:1861
#4  0x00000000006147ce in debug_sync (thd=0x48f3f20, sync_point_name=0xf12440 "before_lock_tables_takes_lock", name_len=29) at /usr/src/mysql-5.6.28/sql/debug_sync.cc:1973
#5  0x00000000007604bd in lock_tables (thd=0x48f3f20, tables=0x4a948e0, count=0, flags=0) at /usr/src/mysql-5.6.28/sql/sql_base.cc:6046
#6  0x00000000008082be in mysql_select (thd=0x48f3f20, tables=0x4a948e0, wild_num=0, fields=..., conds=0x0, order=0x48f6680, group=0x48f65b8, having=0x0, select_options=2684619520, result=0x4a955c8, unit=0x48f5e70, select_lex=0x48f64b8) at /usr/src/mysql-5.6.28/sql/sql_select.cc:1202
#7  0x000000000080854d in handle_select (thd=0x48f3f20, result=0x4a955c8, setup_tables_done_option=0) at /usr/src/mysql-5.6.28/sql/sql_select.cc:110
#8  0x00000000007cdc4e in execute_sqlcom_select (thd=0x48f3f20, all_tables=0x4a948e0) at /usr/src/mysql-5.6.28/sql/sql_parse.cc:5134
#9  0x00000000007cf185 in mysql_execute_command (thd=0x48f3f20) at /usr/src/mysql-5.6.28/sql/sql_parse.cc:2656
#10 0x00000000007d67c4 in mysql_parse (thd=0x48f3f20, rawbuf=0x4a946c0 "show databases", length=14, parser_state=0x7f7c2f1fd910) at /usr/src/mysql-5.6.28/sql/sql_parse.cc:6386
#11 0x00000000007d83f4 in dispatch_command (command=COM_QUERY, thd=0x48f3f20, packet=0x4a8c251 "show databases", packet_length=14) at /usr/src/mysql-5.6.28/sql/sql_parse.cc:1340
#12 0x00000000007d9c80 in do_command (thd=0x48f3f20) at /usr/src/mysql-5.6.28/sql/sql_parse.cc:1037
#13 0x000000000078e3fb in do_handle_one_connection (thd_arg=0x48f3f20) at /usr/src/mysql-5.6.28/sql/sql_connect.cc:982
#14 0x000000000078e4c1 in handle_one_connection (arg=0x48f3f20) at /usr/src/mysql-5.6.28/sql/sql_connect.cc:898
#15 0x0000000000b11172 in pfs_spawn_thread (arg=0x479cd00) at /usr/src/mysql-5.6.28/storage/perfschema/pfs.cc:1860
#16 0x00007f7c989c883d in start_thread () from /lib64/libpthread.so.0
#17 0x00007f7c97e75fdd in clone () from /lib64/libc.so.6
#18 0x0000000000000000 in ?? ()

sql_base.cc:6046

DEBUG_SYNC(thd, "before_lock_tables_takes_lock");

if (! (thd->lock= mysql_lock_tables(thd, start, (uint) (ptr - start),
flags)))
DBUG_RETURN(TRUE);

DEBUG_SYNC(thd, "after_lock_tables_takes_lock");

sql_base.cc:1351

void close_thread_tables(THD *thd)
{
TABLE *table;
DBUG_ENTER("close_thread_tables");

#ifdef EXTRA_DEBUG
DBUG_PRINT("tcache", ("open tables:"));
for (table= thd->open_tables; table; table= table->next)
DBUG_PRINT("tcache", ("table: '%s'.'%s' 0x%lx", table->s->db.str,
table->s->table_name.str, (long) table));
#endif

#if defined(ENABLED_DEBUG_SYNC)
/* debug_sync may not be initialized for some slave threads */
if (thd->debug_sync_control)
DEBUG_SYNC(thd, "before_close_thread_tables");
#endif

DBUG_ASSERT(thd->transaction.stmt.is_empty() || thd->in_sub_stmt ||
(thd->state_flags & Open_tables_state::BACKUPS_AVAIL));

/* Detach MERGE children after every statement. Even under LOCK TABLES. */
for (table= thd->open_tables; table; table= table->next)
{
/* Table might be in use by some outer statement. */
DBUG_PRINT("tcache", ("table: '%s'  query_id: %lu",
table->s->table_name.str, (ulong) table->query_id));
if (thd->locked_tables_mode <= LTM_LOCK_TABLES ||
table->query_id == thd->query_id)
{
DBUG_ASSERT(table->file);
table->file->extra(HA_EXTRA_DETACH_CHILDREN);
}
}

会话3：

mysql> SET DEBUG_SYNC= 'now WAIT_FOR opened';
Query OK, 0 rows affected (0.00 sec)

mysql> SET DEBUG_SYNC= 'after_flush_unlock SIGNAL flushed';
Query OK, 0 rows affected (0.01 sec)

mysql> FLUSH TABLE t1;
Query OK, 0 rows affected (0.20 sec)

会话1：

mysql> insert into t2 select 1;
Query OK, 1 row affected (1 min 25.42 sec)
Records: 1  Duplicates: 0  Warnings: 0

http://www.cnblogs.com/cchust/p/4564741.html

上一篇文章说明了bug出现的原因和原理分析，要修复bug似乎已经水到渠成了，但远没有这么简单，只因为“并发”。要修复问题，首先要做的第一件事情是稳定的复现问题。由于数据库系统是一个并发系统，并且这个bug只有一定的概率出现，更说明了多个线程在一定的执行序列情况下才会出现这个bug。在没有用户请求的情况下，mysql自身的线程就很多，比如主线程，IO线程，监控线程，监听线程等；有用户请求的情况下，还会分配工作线程为用户服务。我们只找和bug相关的线程：purge线程，IO线程，工作线程。Purge线程主要工作是执行purge操作，产生IBUF_OP_DELETE操作；工作线程则主要执行DELETE，INSERT语句，产生IBUF_OP_INSERT和IBUF_OP_DELETE_MARK操作；IO线程则是IBUF的merge操作。为达到重现bug的目的，我们需要产生IBUF_OP_DELETE_MARK，IBUF_OP_INSERT和IBUF_OP_DELETE序列。由于这里面涉及到purge线程和用户线程，因此涉及一个协同问题。如何协同？

DEBUG_SYNC

DEBUG_SYNC是mysql源码中自带的宏，通过信号的方式实现多个线程间的同步。假设存在两个线程thread-1(A,B)，thread-2(a,b)，A,B和a,b分别是thread-1和thread-2的执行顺序。为了得到AaBb执行序列，可以通过DEBUG_SYNC实现。

1) 源代码中，设置同步点

Session-1(thread-1)	Session-2(thread-2)
A	a
DEBUG_SYNC(“after_A”)	DEBUG_SYNC(“after_a”)
B	b
DEBUG_SYNC(“after_B”)

2) Session设置

Session-1(thread-1)	Session-2(thread-2)
set debug_sync="after_Asignal stepA wait_for stepa"; set debug_sync=”after_Bsingal stepB”;	set debug_sync = "nowwait_for stepA "; set debug_sync = "after_asignal stepa wait_for stepB";
A	a
B	b

通过在代码中设置同步点，以及在会话中设置同步关系即可以实现在并发环境下稳定地得到AaBb序列。注意到2)中的蓝色字体表示同步点，红色字体signal和 wait_for表示动作。比如“after_A signal stepA wait_for stepa”表示执行到同步点after_A后，发出信号after_A，并且等待stepa信号的到来。另外，其中now是一个特殊的同步点，表示执行到指定的位置后等待。debug_sync似乎已经完美地解决了同步问题，但问题是，通过debug_sync同步，需要会话设置等待或发出信号动作，如果需要和后台线程同步怎么办？而这个bug恰好又需要和后台线程purge，以及IO线程同步。别着急，有需求，就一定有解，mysql还有另外一种协同方法，DBUG_EXECUTE_IF。

DBUG_EXECUTE_IF

DBUG_EXECUTE_IF原理就很简单了，就是在某一点执行一定的操作，至于是什么操作则没有限制。显然，我们可以在某一个点执行sleep函数，虽然无法做到严格的同步，但也基本能满足需求。DEBUG_EXECUTE_IF的基本格式为：DEBUG_EXECUTE_IF(key, code)，比如为了得到AaBb序列，可以通过DBUG_EXECUTE_IF实现

1) 源代码中，设置操作点

Session-1(thread-1)	Session-2(thread-2)
	DEBUG_EXECUTE_IF (“before_a”,{my_sleep(1)})
A	a
DEBUG_EXECUTE_IF (“after_A”,{my_sleep(3)})	DEBUG_EXECUTE_IF(“after_b”, {my_sleep(5)})
B	b
DEBUG_EXECUTE_IF (“after_B”, {my_sleep(7)})

2) Session设置

这里为了让后台线程也起作用，可以设置全局debug变量，若只想对本session起作用，可以设置会话debug变量。设置后，执行到对应的操作点时，则会额外执行DEBUG_EXECUTE_IF里面的代码。通过sleep方式来同步是一种取巧的方式，在实际情况中，需要不断调整sleep的时间，尽可能保证能按照预设的顺序执行。设置如下：红色部分是加的代码。

set global debug=”+d,before_a, after_A, after_B, after_b”;

实践

对于我们这个案例而言，为了得到指定的IBUF序列(IBUF_OP_DELETE_MARK，IBUF_OP_INSERT和IBUF_OP_DELETE)，首先保证操作页面不出现在buffer_pool中；其次，执行INSERT操作产生的IBUF_OP_INSERT必需先于PURGE执行，最后，在整个过程中页面不能被MERGE，否则也将功亏一篑。对于第一点，可以通过将buffer_pool设置地比较小，然后扫描一个大表达到清理buffer_pool的目的；对于第二点，由于执行IBUF缓存的函数是IBUF_INSERT,针对类型为IBUF_OP_DELETE，强制其等待；对于第三点，在执行merge ibuf的地方，也强制其等待，并且比PURGE等待的时间要更长。具体设置点如下：

/*storage/innobase/ibuf/ibuf0ibuf.cc: ibuf_insert*/
ibuf_insert
{
DBUG_EXECUTE_IF("sleep_ibuf_insert",{
if (op == IBUF_OP_DELETE)
　　my_sleep(3000000);
});

......
　ibuf_insert_low();
}

/* storage/innobase/ibuf/ibuf0ibuf.cc:ibuf_merge_pages*/
ibuf_merge_pages
{
......
　 DBUG_EXECUTE_IF("sleep_ibuf_merge",{my_sleep(5000000);});
　
buf_read_ibuf_merge_pages(sync, space_ids, space_versions, page_nos, *n_pages);//merge操作
}

总结

在整个重现bug的过程中，其实还有很多细节，因为代码中总是会有很多if else的判断，以及特定标记位导致的特殊操作，因此打日志和debug很重要，通过打日志，了解大体执行流程；通过debug来了解细节，从而能掌握关键路径，在关键路径上设置合适的同步点，则能在并发环境下得到想要的执行序列。

参考文档

http://www.gpfeng.com/?p=461

http://hedengcheng.com/?p=238

http://www.cnblogs.com/cchust/p/4544518.html

Session-1(thread-1)	Session-2(thread-2)
A	a
DEBUG_SYNC(“after_A”)	DEBUG_SYNC(“after_a”)
B	b
DEBUG_SYNC(“after_B”)

2) Session设置

Session-1(thread-1)	Session-2(thread-2)
set debug_sync="after_Asignal stepA wait_for stepa"; set debug_sync=”after_Bsingal stepB”;	set debug_sync = "nowwait_for stepA "; set debug_sync = "after_asignal stepa wait_for stepB";
A	a
B	b

Session-1(thread-1)	Session-2(thread-2)
	DEBUG_EXECUTE_IF (“before_a”,{my_sleep(1)})
A	a
DEBUG_EXECUTE_IF (“after_A”,{my_sleep(3)})	DEBUG_EXECUTE_IF(“after_b”, {my_sleep(5)})
B	b
DEBUG_EXECUTE_IF (“after_B”, {my_sleep(7)})

set global debug=”+d,before_a, after_A, after_B, after_b”;

/*storage/innobase/ibuf/ibuf0ibuf.cc: ibuf_insert*/
ibuf_insert
{
DBUG_EXECUTE_IF("sleep_ibuf_insert",{
if (op == IBUF_OP_DELETE)
　　my_sleep(3000000);
});

......
　ibuf_insert_low();
}

/* storage/innobase/ibuf/ibuf0ibuf.cc:ibuf_merge_pages*/
ibuf_merge_pages
{
......
　 DBUG_EXECUTE_IF("sleep_ibuf_merge",{my_sleep(5000000);});
　
buf_read_ibuf_merge_pages(sync, space_ids, space_versions, page_nos, *n_pages);//merge操作
}

inlog.cc (sql):    DEBUG_SYNC(current_thd,"purge_logs_after_lock_index_before_thread_count");
Binlog.cc (sql):    DEBUG_SYNC(thd, "after_show_binlog_event_found_file");
Binlog.cc (sql):      DEBUG_SYNC(thd, "wait_in_show_binlog_events_loop");
Binlog.cc (sql):  DEBUG_SYNC(thd, "after_show_binlog_events");
Binlog.cc (sql):                  DEBUG_SYNC(current_thd, "before_rotate_binlog"););
Binlog.cc (sql):    DEBUG_SYNC(current_thd, "at_purge_logs_before_date");
Binlog.cc (sql):    DEBUG_SYNC(thd, "before_sync_binlog_file");
Binlog.cc (sql):                    DEBUG_SYNC(thd, "before_process_commit_stage_queue"););
Binlog.cc (sql):    DEBUG_SYNC(thd, "ready_to_do_rotation");
CMakeLists.txt (sql):  debug_sync.cc
CMakeLists.txt (unittest\gunit):  debug_sync
Debug_sync-t.cc (unittest\gunit):    DEBUG_SYNC(m_thd,"sync_point");
Debug_sync.cc (sql):  the server code by using the DEBUG_SYNC macro:
Debug_sync.cc (sql):      DEBUG_SYNC(thd, "after_open_tables");
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'after_open_tables SIGNAL opened WAIT_FOR flushed';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'after_open_tables SIGNAL opened WAIT_FOR flushed';
Debug_sync.cc (sql):          SET DEBUG_SYNC= 'now WAIT_FOR opened';
Debug_sync.cc (sql):          SET DEBUG_SYNC= 'after_abort_locks SIGNAL flushed';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'WAIT_FOR flushed NO_CLEAR_EVENT';
Debug_sync.cc (sql):  of DEBUG_SYNC accordingly.
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name SIGNAL sig EXECUTE 3';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name WAIT_FOR sig TIMEOUT 10 EXECUTE 2';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name HIT_LIMIT 3';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name SIGNAL sig EXECUTE 2 HIT_LIMIT 3';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name CLEAR';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'RESET';
Debug_sync.cc (sql):      SET DEBUG_SYNC= 'name TEST';
Debug_sync.cc (sql):  The string to "assign" to the DEBUG_SYNC variable can contain:
Debug_sync.cc (sql):      #define DEBUG_SYNC(thd, sync_point_name)
Debug_sync.cc (sql):  The SET DEBUG_SYNC statement adds a requested action to the array or
Debug_sync.cc (sql):     DEBUG_SYNC(thd, "sync_point_name");
Debug_sync.cc (sql):  point emits a signal. DEBUG_SYNC sets its own proc_info, but restores
Debug_sync.cc (sql):      [DEBUG_SYNC(thd, "sync_point_name");]
Debug_sync.cc (sql):    macro DEBUG_SYNC(thd, sync_point_name). The macro needs a 'thd' argument.
Debug_sync.cc (sql):    DEBUG_SYNC(thd, "thread_end");
Debug_sync.cc (sql):    DEBUG_SYNC(thd, "now");
Debug_sync.cc (sql):      and shall not be reported as a result of SET DEBUG_SYNC.
Debug_sync.cc (sql):    This is called when the DEBUG_SYNC system variable is set.
Debug_sync.cc (sql):        mutex and cond. This would prohibit the use of DEBUG_SYNC
Debug_sync.cc (sql):        it possible to use DEBUG_SYNC framework in scheduler when this
Debug_sync.cc (sql):        mutex and cond. This would prohibit the use of DEBUG_SYNC
Debug_sync.cc (sql):    to be triggered by setting a value to DEBUG_SYNC system variable.
Debug_sync.h (sql):#define DEBUG_SYNC(_thd_, _sync_point_name_)                            \
Debug_sync.h (sql):#define DEBUG_SYNC(_thd_, _sync_point_name_)    /* disabled DEBUG_SYNC */
Filesort.cc (sql):  DEBUG_SYNC(thd, "filesort_start");
Filesort.cc (sql):  DEBUG_SYNC(thd, "after_index_merge_phase1");
Handler.cc (sql):#include "debug_sync.h"         // DEBUG_SYNC
Handler.cc (sql):      DEBUG_SYNC(thd, "ha_commit_trans_after_acquire_commit_lock");
Handler0alter.cc (storage\innobase\handler):    DEBUG_SYNC(user_thd, "innodb_inplace_alter_table_enter");
Handler0alter.cc (storage\innobase\handler):        DEBUG_SYNC(user_thd, "innodb_after_inplace_alter_table");
Handler0alter.cc (storage\innobase\handler):    DEBUG_SYNC(user_thd, "innodb_alter_commit_after_lock_table");
Ha_innodb.cc (storage\innobase\handler):#include <debug_sync.h> // DEBUG_SYNC
Ha_innodb.cc (storage\innobase\handler):    DEBUG_SYNC(user_thd, "ib_after_row_insert");
Ha_innodb.cc (storage\innobase\handler):    DEBUG_SYNC(thd, "after_innobase_rename_table");
Ha_myisammrg.cc (storage\myisammrg):  DEBUG_SYNC(current_thd, "before_myisammrg_attach");
Ha_partition.cc (sql):  DEBUG_SYNC(ha_thd(), "before_rename_partitions");
Ha_partition.cc (sql):  DEBUG_SYNC(ha_thd(), "partition_open_error");
Item_func.cc (sql):  DEBUG_SYNC(current_thd, "before_acos_function");
Item_func.cc (sql):  DEBUG_SYNC(current_thd, "after_getting_user_level_lock_info");
Item_func.cc (sql):  DEBUG_SYNC(current_thd, "after_getting_user_level_lock_info");
Item_subselect.cc (sql):  DEBUG_SYNC(thd, "before_index_end_in_subselect");
Lock.cc (sql):  DEBUG_SYNC(thd, "after_wait_locked_schema_name");
Lock.cc (sql):  DEBUG_SYNC(thd, "before_wait_locked_pname");
Lock.cc (sql):  DEBUG_SYNC(thd, "after_wait_locked_pname");
Mdl-t.cc (unittest\gunit):  We don't need DEBUG_SYNC functionality in a unit test.
Mdl.cc (sql):  DEBUG_SYNC(get_thd(), "mdl_acquire_lock_wait");
Mdl.cc (sql):  DEBUG_SYNC(get_thd(), "mdl_upgrade_lock");
Mdl.h (sql):     This one is only used for DEBUG_SYNC.
Mysqld.cc (sql):    DEBUG_SYNC here, but that's not possible because the THD's debug
Mysqld.cc (sql):  DEBUG_SYNC(thd, "dsync_show_heartbeat_period");
Rpl_master.cc (sql):  DEBUG_SYNC(thd, "show_binlogs_after_lock_log_before_lock_index");
Rpl_slave.cc (sql):    DEBUG_SYNC(thd, "wait_after_lock_active_mi_and_rli_data_lock_is_acquired");
Rpl_slave.cc (sql):  DEBUG_SYNC(thd, "after_start_slave");
Semisync_master.cc (plugin\semisync):    DEBUG_SYNC(current_thd, "rpl_semisync_master_commit_trx_before_lock");
Sql_admin.cc (sql):#include "debug_sync.h"                      // DEBUG_SYNC
Sql_admin.cc (sql):      DEBUG_SYNC(thd, "after_admin_flush");
Sql_admin.cc (sql):      DEBUG_SYNC(thd, "ha_admin_try_alter");
Sql_admin.cc (sql):        DEBUG_SYNC(thd, "ha_admin_open_ltable");
Sql_base.cc (sql):    DEBUG_SYNC(thd, "after_flush_unlock");
Sql_base.cc (sql):    DEBUG_SYNC(thd, "before_close_thread_tables");
Sql_base.cc (sql):      DEBUG_SYNC(thd, "before_open_table_wait_refresh");
Sql_base.cc (sql):    DEBUG_SYNC(thd, "after_open_table_mdl_shared");
Sql_base.cc (sql):        DEBUG_SYNC(thd, "before_upgrading_lock_from_S_to_X_for_create_table");
Sql_base.cc (sql):        DEBUG_SYNC(thd, "after_upgrading_lock_from_S_to_X_for_create_table");
Sql_base.cc (sql):    DEBUG_SYNC(m_thd, "recover_ot_repair");
Sql_base.cc (sql):        DEBUG_SYNC(thd, "after_shared_lock_pname");
Sql_base.cc (sql):  DEBUG_SYNC(thd, "open_and_process_table");
Sql_base.cc (sql):      DEBUG_SYNC(thd, "open_tables_after_open_and_process_table");
Sql_base.cc (sql):    DEBUG_SYNC(thd, "before_lock_tables_takes_lock");
Sql_base.cc (sql):    DEBUG_SYNC(thd, "after_lock_tables_takes_lock");
Sql_cache.cc (sql):#include "debug_sync.h"                         // DEBUG_SYNC
Sql_cache.cc (sql):      DEBUG_SYNC(thd, name);              \
Sql_cache.cc (sql):  DEBUG_SYNC(thd, "wait_after_query_cache_invalidate");
Sql_cache.cc (sql):  DEBUG_SYNC(thd, "wait_in_query_cache_invalidate1");
Sql_cache.cc (sql):  DEBUG_SYNC(thd, "wait_in_query_cache_invalidate2");
Sql_class.cc (sql):  DEBUG_SYNC(this, "thd_cleanup_start");
Sql_class.cc (sql):    DEBUG_SYNC is used in commit code.
Sql_cursor.cc (sql):  DEBUG_SYNC(thd, "after_table_close");
Sql_db.cc (sql):    DEBUG_SYNC(thd, "after_freeing_thd_db");
Sql_db.cc (sql):  DEBUG_SYNC(thd, "before_db_dir_check");
Sql_insert.cc (sql):      DEBUG_SYNC(thd, "before_write_delayed");
Sql_insert.cc (sql):      DEBUG_SYNC(thd, "after_write_delayed");
Sql_insert.cc (sql):      DEBUG_SYNC(thd, "write_row_replace");
Sql_insert.cc (sql):    DEBUG_SYNC(thd, "write_row_noreplace");
Sql_insert.cc (sql):  DEBUG_SYNC(thd,"create_table_select_before_create");
Sql_insert.cc (sql):      DEBUG_SYNC(thd,"create_table_select_before_open");
Sql_insert.cc (sql):  DEBUG_SYNC(thd,"create_table_select_before_check_if_exists");
Sql_insert.cc (sql):  DEBUG_SYNC(thd,"create_table_select_before_lock");
Sql_optimizer.cc (sql):#include "debug_sync.h"          // DEBUG_SYNC
Sql_optimizer.cc (sql):  DEBUG_SYNC(thd, "before_join_optimize");
Sql_parse.cc (sql):  DEBUG_SYNC(thd, "before_do_command_net_read");
Sql_parse.cc (sql):    DEBUG_SYNC(thd,"before_execute_sql_command");
Sql_parse.cc (sql):    DEBUG_SYNC(thd, "execute_command_after_close_tables");
Sql_parse.cc (sql):  DEBUG_SYNC(thd, "after_table_open");
Sql_partition.cc (sql):    DEBUG_SYNC(current_thd, "swap_partition_first_row_read");
Sql_partition_admin.cc (sql):#include "debug_sync.h"                     // DEBUG_SYNC
Sql_partition_admin.cc (sql):  DEBUG_SYNC(thd, "swap_partition_after_compare_tables");
Sql_partition_admin.cc (sql):  DEBUG_SYNC(thd, "swap_partition_after_wait");
Sql_partition_admin.cc (sql):  DEBUG_SYNC(thd, "swap_partition_before_rename");
Sql_plugin.cc (sql):  DEBUG_SYNC(thd, "acquired_LOCK_plugin");
Sql_reload.cc (sql):  DEBUG_SYNC(thd,"flush_tables_with_read_lock_after_acquire_locks");
Sql_show.cc (sql):    DEBUG_SYNC(thd,"before_copying_threads");
Sql_show.cc (sql):    DEBUG_SYNC(thd,"after_copying_threads");
Sql_show.cc (sql):                           DEBUG_SYNC(thd, "processlist_after_LOCK_thd_count_before_LOCK_thd_data");
Sql_show.cc (sql):                      DEBUG_SYNC(thd, "processlist_after_LOCK_thd_count_before_LOCK_thd_data");
Sql_show.cc (sql):  DEBUG_SYNC(thd, "after_open_table_ignore_flush");
Sql_show.cc (sql):            DEBUG_SYNC(thd, "before_open_in_get_all_tables");
Sql_show.cc (sql):    DEBUG_SYNC(thd, "get_schema_column");
Sql_show.cc (sql):  DEBUG_SYNC(thd, "acquired_LOCK_system_variables_hash");
Sql_show.cc (sql):  DEBUG_SYNC(thd, "before_preparing_global_status_array");
Sql_show.cc (sql):  DEBUG_SYNC(thd, "after_preparing_global_status_array");
Sql_table.cc (sql):    DEBUG_SYNC(thd, "rm_table_no_locks_before_delete_table");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "rm_table_no_locks_before_binlog");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "locked_table_name");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "create_table_like_after_open");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "create_table_like_before_binlog");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_inplace_after_lock_upgrade");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_inplace_after_lock_downgrade");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_inplace_before_commit");
Sql_table.cc (sql):      DEBUG_SYNC(thd,"alter_table_enable_indexes");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_before_open_tables");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_opened_table");
Sql_table.cc (sql):      DEBUG_SYNC(thd, "locked_table_name");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_before_create_table_no_lock");
Sql_table.cc (sql):    DEBUG_SYNC(thd, "alter_table_copy_after_lock_upgrade");
Sql_table.cc (sql):    DEBUG_SYNC(thd, "alter_table_manage_keys");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_before_rename_result_table");
Sql_table.cc (sql):  DEBUG_SYNC(thd, "alter_table_before_main_binlog");
Sql_tmp_table.cc (sql):  DEBUG_SYNC(thd, "tmp_table_created");
Sql_truncate.cc (sql):#include "debug_sync.h"  // DEBUG_SYNC
Sql_truncate.cc (sql):    DEBUG_SYNC(thd, "upgrade_lock_for_truncate");
Sys_vars.cc (sql):#include "debug_sync.h"                         // DEBUG_SYNC
Sys_vars.cc (sql):  DEBUG_SYNC(thd, "fix_slave_net_timeout");
Table.cc (sql):  DEBUG_SYNC(thd, "flush_complete");
Table.cc (sql):  DEBUG_SYNC(thd, "share_destroyed");
Thread_pool_priv.h (include\mysql):  A thread pool can also use DEBUG_SYNC and must thus include
Transaction.cc (sql):#include "debug_sync.h"         // DEBUG_SYNC
Transaction.cc (sql):      DEBUG_SYNC(thd, "trans_xa_commit_after_acquire_commit_lock");
Tztime.cc (sql):      DEBUG_SYNC(thd, "my_tz_find");

DEBUG_EXECUTE_IF主要用于当设置了某个关键字key时，执行后面code

可以简单的表示为:

DEBUG_EXECUTE_IF(key, code)

例如在open_and_lock_tables函数中.

5527 if (open_tables(thd, &tables, &counter, flags, prelocking_strategy))
5528 goto err;
5529
5530 DBUG_EXECUTE_IF("sleep_open_and_lock_after_open", {
5531 const char *old_proc_info= thd->proc_info;
5532 thd->proc_info= "DBUG sleep";
5533 my_sleep(6000000);
5534 thd->proc_info= old_proc_info;});
5535
5536 if (lock_tables(thd, tables, counter, flags))
5537 goto err;

那么如何让其生效呢，执行如下语句即可:

set session debug=”+d, sleep_open_and_lock_after_open”

这时候当进入这个函数时，在执行完open_tables语句后，就会设置thd的状态为DBUG sleep，再sleep 6秒钟，然后再调用lock_tables函数

—————-

另外我们在写test case时，也可能用到用户层的锁，使用SQL FUNCTION的方法实现:

GET_LOCK(str, timeout)

—尝试获取一个名为str的锁，等待timeout，返回1表示获取锁成功

IS_FREE_LOCK(str)

—检查名为str的锁是否已经被释放

IS_USED_LOCK(str)

—检查名为str的锁是否已经被占用，如果是，返回占有该锁的线程ID，否则返回NULL

RELEASE_LOCK(str)

—释放名为str的锁

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