級聯slave的延遲計算和query event exe time獲取方法

原始碼5.7.22

一、級聯時間計算方式

比如A->B->C那麼C的延遲是計算B還是A的。因為Event的中timestamp沒變，但是C計算時間差值卻是以B為準。如果時鐘同步的情況下，其實基本可以考慮為A的。計算方法可以參考我的《深入理解MySQL主從原理》專欄
具體可以點選：ttps://j.youzan.com/yEY_Xi

邏輯如下：

級聯中的Event依然是主庫的時間，因此其延遲還是相對主庫而言。
雖然apply_event_and_update_pos函式中由設定為當前時間thd->set_time()
但是最終設定還是在Query_log_event::do_apply_event和Query_log_event::do_apply_event中的
的
THD::set_time (this=0x7ffe74007da0, t=0x7ffe74007828)
因為只有做了資料庫修改才會觸發記錄Event的工作
設個設定就是設定為event header的timestamp，因此還是級聯中記錄的Event的時間還是
主庫的時間，計算延遲就是相對主庫的時間。
棧幀
#0  THD::set_time (this=0x7ffe74007da0, t=0x7ffe7493c4d0) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/sql_class.h:3526
#1  0x00000000018459ab in Query_log_event::do_apply_event (this=0x7ffe7493c3b0, rli=0x676be60, query_arg=0x7ffe740061dc "BEGIN", q_len_arg=5)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:4714
#2  0x0000000001845287 in Query_log_event::do_apply_event (this=0x7ffe7493c3b0, rli=0x676be60)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:4567
#3  0x00000000018420d4 in Log_event::apply_event (this=0x7ffe7493c3b0, rli=0x676be60) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:3570
#4  0x00000000018bc078 in apply_event_and_update_pos (ptr_ev=0x7fffec094830, thd=0x7ffe74007da0, rli=0x676be60)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:4766
#5  0x00000000018bd773 in exec_relay_log_event (thd=0x7ffe74007da0, rli=0x676be60) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:5300
#6  0x00000000018c46e4 in handle_slave_sql (arg=0x6675d30) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:7543
#7  0x0000000001945620 in pfs_spawn_thread (arg=0x7ffe7c02c6c0) at /root/mysqlall/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#8  0x00007ffff7bc6aa1 in start_thread () from /lib64/libpthread.so.0
#9  0x00007ffff6719bcd in clone () from /lib64/libc.so.6
#0  THD::set_time (this=0x7ffe74007da0, t=0x7ffe7493c4d0) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/sql_class.h:3526
#1  0x00000000018459ab in Query_log_event::do_apply_event (this=0x7ffe7493c3b0, rli=0x676be60, query_arg=0x7ffe740061dc "BEGIN", q_len_arg=5)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:4714
#2  0x0000000001845287 in Query_log_event::do_apply_event (this=0x7ffe7493c3b0, rli=0x676be60)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:4567
#3  0x00000000018420d4 in Log_event::apply_event (this=0x7ffe7493c3b0, rli=0x676be60) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/log_event.cc:3570
#4  0x00000000018bc078 in apply_event_and_update_pos (ptr_ev=0x7fffec094830, thd=0x7ffe74007da0, rli=0x676be60)
    at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:4766
#5  0x00000000018bd773 in exec_relay_log_event (thd=0x7ffe74007da0, rli=0x676be60) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:5300
#6  0x00000000018c46e4 in handle_slave_sql (arg=0x6675d30) at /root/mysqlall/percona-server-locks-detail-5.7.22/sql/rpl_slave.cc:7543
#7  0x0000000001945620 in pfs_spawn_thread (arg=0x7ffe7c02c6c0) at /root/mysqlall/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#8  0x00007ffff7bc6aa1 in start_thread () from /lib64/libpthread.so.0
#9  0x00007ffff6719bcd in clone () from /lib64/libc.so.6
query map event在修改的第一條資料 記錄時間 這個時間肯定是Log_event::apply_event的時間，
GTID自然是在最後commit的時候 ,XID EVENT也是正確的主庫時間。
實際上第一個THD::set_time(header->timestamp)後user_time 就正確，下面的邏輯不會設定為當前時間。
inline void set_time()
  {
    start_utime= utime_after_lock= my_micro_time();
    if (user_time.tv_sec || user_time.tv_usec)
    {
      start_time= user_time;
    }
    else
      my_micro_time_to_timeval(start_utime, &start_time);
#ifdef HAVE_PSI_THREAD_INTERFACE
    PSI_THREAD_CALL(set_thread_start_time)(start_time.tv_sec);
#endif
  }
但是主庫dispatch_command的時候不會設定user_time user_time為0，因此設定為當前時間。
#0  THD::set_time (this=0x7ffedc0009c0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_class.h:3514
#1  0x00000000015c5fe8 in dispatch_command (thd=0x7ffedc0009c0, com_data=0x7fffec5bdd70, command=COM_QUERY)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1247
#2  0x00000000015c58ff in do_command (thd=0x7ffedc0009c0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1021
#3  0x000000000170e578 in handle_connection (arg=0x67d01a0) at /mysqldata/percona-server-locks-detail-5.7.22/sql/conn_handler/connection_handler_per_thread.cc:312
#4  0x0000000001945538 in pfs_spawn_thread (arg=0x67c9dc0) at /mysqldata/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#5  0x00007ffff7bcfaa1 in start_thread () from /lib64/libpthread.so.0
#6  0x00007ffff6b37c4d in clone () from /lib64/libc.so.6

二、header中的timestamp和query_event的exe time計算方式

common_header：中的時間來自 命令發起的時間。下面是其初始化  
Log_event::Log_event(THD* thd_arg, uint16 flags_arg,
                     enum_event_cache_type cache_type_arg,
                     enum_event_logging_type logging_type_arg,
                     Log_event_header *header, Log_event_footer *footer)
  : is_valid_param(false), temp_buf(0), exec_time(0),
    event_cache_type(cache_type_arg), event_logging_type(logging_type_arg),
    crc(0), common_header(header), common_footer(footer), thd(thd_arg)
{
  server_id= thd->server_id;
  common_header->unmasked_server_id= server_id;
  common_header->when= thd->start_time;
  common_header->log_pos= 0;
  common_header->flags= flags_arg;
}
dispatch_command呼叫時間
Query_log_event::Query_log_event(THD* thd_arg, const char* query_arg,
                 size_t query_length, bool using_trans,
                 bool immediate, bool suppress_use,
                                 int errcode, bool ignore_cmd_internals)
: binary_log::Query_event(query_arg,
                          thd_arg->catalog().str,
                          thd_arg->db().str,
                          query_length,
                          thd_arg->thread_id(),
                          thd_arg->variables.sql_mode,
                          thd_arg->variables.auto_increment_increment,
                          thd_arg->variables.auto_increment_offset,
                          thd_arg->variables.lc_time_names->number,
                          (ulonglong)thd_arg->table_map_for_update,
                          errcode,
                          thd_arg->db().str ? strlen(thd_arg->db().str) : 0,
                          thd_arg->catalog().str ? strlen(thd_arg->catalog().str) : 0),
  Log_event(thd_arg,
            (thd_arg->thread_specific_used ? LOG_EVENT_THREAD_SPECIFIC_F :
             0) |
            (suppress_use ? LOG_EVENT_SUPPRESS_USE_F : 0),
            using_trans ? Log_event::EVENT_TRANSACTIONAL_CACHE :
                          Log_event::EVENT_STMT_CACHE,
            Log_event::EVENT_NORMAL_LOGGING,
            header(), footer()),
  data_buf(0)
{
  DBUG_EXECUTE_IF("debug_lock_before_query_log_event",
                  DBUG_SYNC_POINT("debug_lock.before_query_log_event", 10););
  /* save the original thread id; we already know the server id */
  slave_proxy_id= thd_arg->variables.pseudo_thread_id;
  if (query != 0)
    is_valid_param= true;
  /*
  exec_time calculation has changed to use the same method that is used
  to fill out "thd_arg->start_time"
  */
  struct timeval end_time;
  ulonglong micro_end_time= my_micro_time();//這裡獲取時間 query event
  my_micro_time_to_timeval(micro_end_time, &end_time);
  exec_time= end_time.tv_sec - thd_arg->start_time.tv_sec;//這裡計算時間