show master/slave status求根溯源
show master/slave status分别是查看主数据库以及副数据库的状态，是一种能查看主从复制运行情况的方式。
这里仅仅讨论linux下的nysql5.7.13版本的执行情况
一、show master status
开始与show global status类似，都是分配一个线程去处理该连接的命令（图1）
图1 show master status命令处理流程
1.在sql_yacc.cc:yyparse中
、
（1）初始化内存
（2）初始化解析后命令选项 SQLCOM_SHOW_MASTER_STAT
（3）初始化为单查询（此处无用）
2.show master status命令处理流程
图2. show_master_status的处理流程
（1）在mysql_execute_command（图2#3）中
进入该选项分支
case SQLCOM_SHOW_MASTER_STAT:
{
/* Accept one of two privileges */
if (check_global_access(thd, SUPER_ACL | REPL_CLIENT_ACL))
goto error;
res = show_master_status(thd);
break;
}
（2）在show_master_status（图2#2）中
1）初始化发送格式格式
field_list.push_back(new Item_empty_string("File", FN_REFLEN));
field_list.push_back(new Item_return_int("Position",,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Binlog_Do_DB",));
field_list.push_back(new Item_empty_string("Binlog_Ignore_DB",));
field_list.push_back(new Item_empty_string("Executed_Gtid_Set",
gtid_set_size));
if (thd->send_result_metadata(&field_list,
Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF))
2）储存内容并发送
protocol->start_row(); if (mysql_bin_log.is_open())
{
LOG_INFO li;
mysql_bin_log.get_current_log(&li);
size_t dir_len = dirname_length(li.log_file_name);
protocol->store(li.log_file_name + dir_len, &my_charset_bin);
protocol->store((ulonglong) li.pos);
store(protocol, binlog_filter->get_do_db());
store(protocol, binlog_filter->get_ignore_db());
protocol->store(gtid_set_buffer, &my_charset_bin);
if (protocol->end_row())
{
my_free(gtid_set_buffer);
DBUG_RETURN(true);
}
}
（3）在raw_get_current_log（图2#1）中
int MYSQL_BIN_LOG::get_current_log(LOG_INFO* linfo, bool need_lock_log/*true*/)
{
if (need_lock_log)
mysql_mutex_lock(&LOCK_log);
int ret = raw_get_current_log(linfo);
if (need_lock_log)
mysql_mutex_unlock(&LOCK_log);
return ret;
}
主要的处理函数就是raw_get_current_log
（4）在raw_get_current_log（图2#0）中
在binlog的那点事中的写位置定位有详细解释，这里不再赘述。
二、show slave status
图3 show slave status命令处理流程
1.在sql_yacc.cc:yyparse中
1）初始化信息
2）初始化信道
3）初始化执行命令类型
4）使用单查询（此处无用）
2.命令执行流程
图4 show slave status命令处理
（1）同样地在mysql_execute_command（图4#3）中
case SQLCOM_SHOW_MASTER_STAT:
{
/* Accept one of two privileges */
if (check_global_access(thd, SUPER_ACL | REPL_CLIENT_ACL))
goto error;
res = show_master_status(thd);
break;
}
（2）在show_master_status（图4#2）中
由于在解析中看到lex->mi.for_channel=false,为此进入此分支
if (!lex->mi.for_channel)
res= show_slave_status(thd);
（3）在show_master_status（图4#3）中
1）清空每一信道的内存
for (mi_map::iterator it= channel_map.begin(); it!=channel_map.end(); it++)
{
mi= it->second;
/*
The following statement is needed because, when mi->host[0]=0
we don't alloc memory for retried_gtid_set. However, we try
to free it at the end, causing a crash. To be on safeside,
we initialize it to NULL, so that my_free() takes care of it.
*/
io_gtid_set_buffer_array[idx]= NULL; if (mi != NULL && mi->host[])
{
const Gtid_set* io_gtid_set= mi->rli->get_gtid_set(); /*
@todo: a single memory allocation improves speed,
instead of doing it for each loop
*/ if ((io_gtid_set_size=
io_gtid_set->to_string(&io_gtid_set_buffer_array[idx])) < )
{
my_eof(thd);
my_free(sql_gtid_set_buffer); for (uint i= ; i < idx -; i++)
{
my_free(io_gtid_set_buffer_array[i]);
}
my_free(io_gtid_set_buffer_array); global_sid_lock->unlock();
DBUG_RETURN(true);
}
else
max_io_gtid_set_size= max_io_gtid_set_size > io_gtid_set_size ?
max_io_gtid_set_size : io_gtid_set_size;
}
idx++;
}
2）在show_slave_status_metadata，申请内存
void show_slave_status_metadata(List<Item> &field_list,
int io_gtid_set_size, int sql_gtid_set_size)
{ field_list.push_back(new Item_empty_string("Slave_IO_State", ));
field_list.push_back(new Item_empty_string("Master_Host",
HOSTNAME_LENGTH+));
field_list.push_back(new Item_empty_string("Master_User",
USERNAME_LENGTH+));
field_list.push_back(new Item_return_int("Master_Port", ,MYSQL_TYPE_LONG));
field_list.push_back(new Item_return_int("Connect_Retry", ,
MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Master_Log_File", FN_REFLEN));
field_list.push_back(new Item_return_int("Read_Master_Log_Pos", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Relay_Log_File", FN_REFLEN));
field_list.push_back(new Item_return_int("Relay_Log_Pos", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Relay_Master_Log_File",
FN_REFLEN));
field_list.push_back(new Item_empty_string("Slave_IO_Running", ));
field_list.push_back(new Item_empty_string("Slave_SQL_Running", ));
field_list.push_back(new Item_empty_string("Replicate_Do_DB", ));
field_list.push_back(new Item_empty_string("Replicate_Ignore_DB", ));
field_list.push_back(new Item_empty_string("Replicate_Do_Table", ));
field_list.push_back(new Item_empty_string("Replicate_Ignore_Table", ));
field_list.push_back(new Item_empty_string("Replicate_Wild_Do_Table", ));
field_list.push_back(new Item_empty_string("Replicate_Wild_Ignore_Table",
));
field_list.push_back(new Item_return_int("Last_Errno", , MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Last_Error", ));
field_list.push_back(new Item_return_int("Skip_Counter", ,
MYSQL_TYPE_LONG));
field_list.push_back(new Item_return_int("Exec_Master_Log_Pos", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_return_int("Relay_Log_Space", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Until_Condition", ));
field_list.push_back(new Item_empty_string("Until_Log_File", FN_REFLEN));
field_list.push_back(new Item_return_int("Until_Log_Pos", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Master_SSL_Allowed", ));
field_list.push_back(new Item_empty_string("Master_SSL_CA_File", FN_REFLEN));
field_list.push_back(new Item_empty_string("Master_SSL_CA_Path", FN_REFLEN));
field_list.push_back(new Item_empty_string("Master_SSL_Cert", FN_REFLEN));
field_list.push_back(new Item_empty_string("Master_SSL_Cipher", FN_REFLEN));
field_list.push_back(new Item_empty_string("Master_SSL_Key", FN_REFLEN));
field_list.push_back(new Item_return_int("Seconds_Behind_Master", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Master_SSL_Verify_Server_Cert",
));
field_list.push_back(new Item_return_int("Last_IO_Errno", , MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Last_IO_Error", ));
field_list.push_back(new Item_return_int("Last_SQL_Errno", , MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Last_SQL_Error", ));
field_list.push_back(new Item_empty_string("Replicate_Ignore_Server_Ids",
FN_REFLEN));
field_list.push_back(new Item_return_int("Master_Server_Id", sizeof(ulong),
MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Master_UUID", UUID_LENGTH));
field_list.push_back(new Item_empty_string("Master_Info_File",
* FN_REFLEN));
field_list.push_back(new Item_return_int("SQL_Delay", , MYSQL_TYPE_LONG));
field_list.push_back(new Item_return_int("SQL_Remaining_Delay", , MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Slave_SQL_Running_State", ));
field_list.push_back(new Item_return_int("Master_Retry_Count", ,
MYSQL_TYPE_LONGLONG));
field_list.push_back(new Item_empty_string("Master_Bind", HOSTNAME_LENGTH+));
field_list.push_back(new Item_empty_string("Last_IO_Error_Timestamp", ));
field_list.push_back(new Item_empty_string("Last_SQL_Error_Timestamp", ));
field_list.push_back(new Item_empty_string("Master_SSL_Crl", FN_REFLEN));
field_list.push_back(new Item_empty_string("Master_SSL_Crlpath", FN_REFLEN));
field_list.push_back(new Item_empty_string("Retrieved_Gtid_Set",
io_gtid_set_size));
field_list.push_back(new Item_empty_string("Executed_Gtid_Set",
sql_gtid_set_size));
field_list.push_back(new Item_return_int("Auto_Position", sizeof(ulong),
MYSQL_TYPE_LONG));
field_list.push_back(new Item_empty_string("Replicate_Rewrite_DB", ));
field_list.push_back(new Item_empty_string("Channel_Name", CHANNEL_NAME_LENGTH));
field_list.push_back(new Item_empty_string("Master_TLS_Version", FN_REFLEN)); }
3）初始化发送协议
if (thd->send_result_metadata(&field_list,
Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF))
{
goto err;
}
4）向各个信道发送要查询的状态
idx=;
for (mi_map::iterator it= channel_map.begin(); it!=channel_map.end(); it++)
{
mi= it->second; if (mi != NULL && mi->host[])
{
if (show_slave_status_send_data(thd, mi, io_gtid_set_buffer_array[idx],
sql_gtid_set_buffer))
goto err; if (protocol->end_row())
goto err;
}
idx++;
}
对于show_slave_status_send_data
bool show_slave_status_send_data(THD *thd, Master_info *mi,
char* io_gtid_set_buffer,
char* sql_gtid_set_buffer)
{
DBUG_ENTER("show_slave_status_send_data"); Protocol *protocol = thd->get_protocol();
char* slave_sql_running_state= NULL; DBUG_PRINT("info",("host is set: '%s'", mi->host)); protocol->start_row(); /*
slave_running can be accessed without run_lock but not other
non-volatile members like mi->info_thd or rli->info_thd, for
them either info_thd_lock or run_lock hold is required.
*/
mysql_mutex_lock(&mi->info_thd_lock);
protocol->store(mi->info_thd ? mi->info_thd->get_proc_info() : "",
&my_charset_bin);
mysql_mutex_unlock(&mi->info_thd_lock); mysql_mutex_lock(&mi->rli->info_thd_lock);
slave_sql_running_state= const_cast<char *>(mi->rli->info_thd ? mi->rli->info_thd->get_proc_info() : "");
mysql_mutex_unlock(&mi->rli->info_thd_lock); mysql_mutex_lock(&mi->data_lock);
mysql_mutex_lock(&mi->rli->data_lock);
mysql_mutex_lock(&mi->err_lock);
mysql_mutex_lock(&mi->rli->err_lock); DEBUG_SYNC(thd, "wait_after_lock_active_mi_and_rli_data_lock_is_acquired");
protocol->store(mi->host, &my_charset_bin);
protocol->store(mi->get_user(), &my_charset_bin);
protocol->store((uint32) mi->port);
protocol->store((uint32) mi->connect_retry);
protocol->store(mi->get_master_log_name(), &my_charset_bin);
protocol->store((ulonglong) mi->get_master_log_pos());
protocol->store(mi->rli->get_group_relay_log_name() +
dirname_length(mi->rli->get_group_relay_log_name()),
&my_charset_bin);
protocol->store((ulonglong) mi->rli->get_group_relay_log_pos());
protocol->store(mi->rli->get_group_master_log_name(), &my_charset_bin);
protocol->store(mi->slave_running == MYSQL_SLAVE_RUN_CONNECT ?
"Yes" : (mi->slave_running == MYSQL_SLAVE_RUN_NOT_CONNECT ?
"Connecting" : "No"), &my_charset_bin);
protocol->store(mi->rli->slave_running ? "Yes":"No", &my_charset_bin);
store(protocol, rpl_filter->get_do_db());
store(protocol, rpl_filter->get_ignore_db()); char buf[];
String tmp(buf, sizeof(buf), &my_charset_bin);
rpl_filter->get_do_table(&tmp);
protocol->store(&tmp);
rpl_filter->get_ignore_table(&tmp);
protocol->store(&tmp);
rpl_filter->get_wild_do_table(&tmp);
protocol->store(&tmp);
rpl_filter->get_wild_ignore_table(&tmp);
protocol->store(&tmp); protocol->store(mi->rli->last_error().number);
protocol->store(mi->rli->last_error().message, &my_charset_bin);
protocol->store((uint32) mi->rli->slave_skip_counter);
protocol->store((ulonglong) mi->rli->get_group_master_log_pos());
protocol->store((ulonglong) mi->rli->log_space_total); const char *until_type= ""; switch (mi->rli->until_condition)
{
case Relay_log_info::UNTIL_NONE:
until_type= "None";
break;
case Relay_log_info::UNTIL_MASTER_POS:
until_type= "Master";
break;
case Relay_log_info::UNTIL_RELAY_POS:
until_type= "Relay";
break;
case Relay_log_info::UNTIL_SQL_BEFORE_GTIDS:
until_type= "SQL_BEFORE_GTIDS";
break;
case Relay_log_info::UNTIL_SQL_AFTER_GTIDS:
until_type= "SQL_AFTER_GTIDS";
break;
case Relay_log_info::UNTIL_SQL_VIEW_ID:
until_type= "SQL_VIEW_ID";
break;
case Relay_log_info::UNTIL_SQL_AFTER_MTS_GAPS:
until_type= "SQL_AFTER_MTS_GAPS";
case Relay_log_info::UNTIL_DONE:
until_type= "DONE";
break;
default:
DBUG_ASSERT();
}
protocol->store(until_type, &my_charset_bin);
protocol->store(mi->rli->until_log_name, &my_charset_bin);
protocol->store((ulonglong) mi->rli->until_log_pos); #ifdef HAVE_OPENSSL
protocol->store(mi->ssl? "Yes":"No", &my_charset_bin);
#else
protocol->store(mi->ssl? "Ignored":"No", &my_charset_bin);
#endif
protocol->store(mi->ssl_ca, &my_charset_bin);
protocol->store(mi->ssl_capath, &my_charset_bin);
protocol->store(mi->ssl_cert, &my_charset_bin);
protocol->store(mi->ssl_cipher, &my_charset_bin);
protocol->store(mi->ssl_key, &my_charset_bin); /*
The pseudo code to compute Seconds_Behind_Master:
if (SQL thread is running)
{
if (SQL thread processed all the available relay log)
{
if (IO thread is running)
print 0;
else
print NULL;
}
else
compute Seconds_Behind_Master;
}
else
print NULL;
*/ if (mi->rli->slave_running)
{
/*
Check if SQL thread is at the end of relay log
Checking should be done using two conditions
condition1: compare the log positions and
condition2: compare the file names (to handle rotation case)
*/
if ((mi->get_master_log_pos() == mi->rli->get_group_master_log_pos()) &&
(!strcmp(mi->get_master_log_name(), mi->rli->get_group_master_log_name())))
{
if (mi->slave_running == MYSQL_SLAVE_RUN_CONNECT)
protocol->store(0LL);
else
protocol->store_null();
}
else
{
long time_diff= ((long)(time() - mi->rli->last_master_timestamp)
- mi->clock_diff_with_master);
/*
Apparently on some systems time_diff can be <0. Here are possible
reasons related to MySQL:
- the master is itself a slave of another master whose time is ahead.
- somebody used an explicit SET TIMESTAMP on the master.
Possible reason related to granularity-to-second of time functions
(nothing to do with MySQL), which can explain a value of -1:
assume the master's and slave's time are perfectly synchronized, and
that at slave's connection time, when the master's timestamp is read,
it is at the very end of second 1, and (a very short time later) when
the slave's timestamp is read it is at the very beginning of second
2. Then the recorded value for master is 1 and the recorded value for
slave is 2. At SHOW SLAVE STATUS time, assume that the difference
between timestamp of slave and rli->last_master_timestamp is 0
(i.e. they are in the same second), then we get 0-(2-1)=-1 as a result.
This confuses users, so we don't go below 0: hence the max(). last_master_timestamp == 0 (an "impossible" timestamp 1970) is a
special marker to say "consider we have caught up".
*/
protocol->store((longlong)(mi->rli->last_master_timestamp ?
max(0L, time_diff) : ));
}
}
else
{
protocol->store_null();
}
protocol->store(mi->ssl_verify_server_cert? "Yes":"No", &my_charset_bin); // Last_IO_Errno
protocol->store(mi->last_error().number);
// Last_IO_Error
protocol->store(mi->last_error().message, &my_charset_bin);
// Last_SQL_Errno
protocol->store(mi->rli->last_error().number);
// Last_SQL_Error
protocol->store(mi->rli->last_error().message, &my_charset_bin);
// Replicate_Ignore_Server_Ids
{
char buff[FN_REFLEN];
ulong i, cur_len;
for (i= , buff[]= , cur_len= ;
i < mi->ignore_server_ids->dynamic_ids.size(); i++)
{
ulong s_id, slen;
char sbuff[FN_REFLEN];
s_id= mi->ignore_server_ids->dynamic_ids[i];
slen= sprintf(sbuff, (i == ? "%lu" : ", %lu"), s_id);
if (cur_len + slen + > FN_REFLEN)
{
/*
break the loop whenever remained space could not fit
ellipses on the next cycle
*/
sprintf(buff + cur_len, "...");
break;
}
cur_len += sprintf(buff + cur_len, "%s", sbuff);
}
protocol->store(buff, &my_charset_bin);
}
// Master_Server_id
protocol->store((uint32) mi->master_id);
protocol->store(mi->master_uuid, &my_charset_bin);
// Master_Info_File
protocol->store(mi->get_description_info(), &my_charset_bin);
// SQL_Delay
protocol->store((uint32) mi->rli->get_sql_delay());
// SQL_Remaining_Delay
if (slave_sql_running_state == stage_sql_thd_waiting_until_delay.m_name)
{
time_t t= my_time(), sql_delay_end= mi->rli->get_sql_delay_end();
protocol->store((uint32)(t < sql_delay_end ? sql_delay_end - t : ));
}
else
protocol->store_null();
// Slave_SQL_Running_State
protocol->store(slave_sql_running_state, &my_charset_bin);
// Master_Retry_Count
protocol->store((ulonglong) mi->retry_count);
// Master_Bind
protocol->store(mi->bind_addr, &my_charset_bin);
// Last_IO_Error_Timestamp
protocol->store(mi->last_error().timestamp, &my_charset_bin);
// Last_SQL_Error_Timestamp
protocol->store(mi->rli->last_error().timestamp, &my_charset_bin);
// Master_Ssl_Crl
protocol->store(mi->ssl_crl, &my_charset_bin);
// Master_Ssl_Crlpath
protocol->store(mi->ssl_crlpath, &my_charset_bin);
// Retrieved_Gtid_Set
protocol->store(io_gtid_set_buffer, &my_charset_bin);
// Executed_Gtid_Set
protocol->store(sql_gtid_set_buffer, &my_charset_bin);
// Auto_Position
protocol->store(mi->is_auto_position() ? : );
// Replicate_Rewrite_DB
rpl_filter->get_rewrite_db(&tmp);
protocol->store(&tmp);
// channel_name
protocol->store(mi->get_channel(), &my_charset_bin);
// Master_TLS_Version
protocol->store(mi->tls_version, &my_charset_bin); mysql_mutex_unlock(&mi->rli->err_lock);
mysql_mutex_unlock(&mi->err_lock);
mysql_mutex_unlock(&mi->rli->data_lock);
mysql_mutex_unlock(&mi->data_lock); DBUG_RETURN(false);
}
在这个函数和show_slave_status_metadata中，我们可以看到每个状态取自那个函数，这样就可以弄明白每个状态的实时更新性
在这里我们关注的是Master_Log_File和 Read_Master_Log_Pos的状态。这是主从同步情况最主要的状态，但是这涉及到slave IO的运行情况，我们下次在slave IO说明
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