show processlist time負數的初探

---

本文主要解釋一下下面兩個語句的相應介面和時間計算方式。

• select * from information_schema.processlist;
• show processlist

歡迎關注我的《深入理解MySQL主從原理 32講 》，如下：

---

一、show processlist

函式介面：mysqld_list_processes

棧幀：

#0  mysqld_list_processes (thd=0x7ffedc008250, user=0x0, verbose=false) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_show.cc:2370
#1  0x00000000015ccaab in mysql_execute_command (thd=0x7ffedc008250, first_level=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:3789
#2  0x00000000015d2fde in mysql_parse (thd=0x7ffedc008250, parser_state=0x7fffec5bd600) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:5901
#3  0x00000000015c6b72 in dispatch_command (thd=0x7ffedc008250, com_data=0x7fffec5bdd70, command=COM_QUERY)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1490
#4  0x00000000015c58ff in do_command (thd=0x7ffedc008250) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1021
#5  0x000000000170e578 in handle_connection (arg=0x5f4fe40) at /mysqldata/percona-server-locks-detail-5.7.22/sql/conn_handler/connection_handler_per_thread.cc:312
#6  0x0000000001945538 in pfs_spawn_thread (arg=0x6809be0) at /mysqldata/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#7  0x00007ffff7bcfaa1 in start_thread () from /lib64/libpthread.so.0
#8  0x00007ffff6b37c4d in clone () from /lib64/libc.so.6

其實這個時間很好理解如下：

• 伺服器時間 - 命令發起的時間
• 從庫SQL執行緒則是 伺服器時間 - Event header的時間（來自主庫）

因此出現負數是可能的。這裡計算時間percona 和 官方版本 不同如下：

官方 5.6.25 .5.7.23 都是（可能出現負數）：

    if (thd_info->start_time)
      protocol->store_long ((longlong) (now - thd_info->start_time));

percona 5.7.22（避免出現負數用0代替）：

if (thd_info->start_time)
    {
      protocol->store_long ((thd_info->start_time > now) ? 0
        : (longlong) (now - thd_info->start_time));
    }

可以看到percona 對計算時間做了邏輯變化，負數會顯示為0。關於負數的測試如下：

二、select * from information_schema.processlist;

函式介面：fill_schema_processlist

棧幀：

#0  Field_long::store (this=0x7ffedc0164c8, nr=-1783905, unsigned_val=false) at /mysqldata/percona-server-locks-detail-5.7.22/sql/field.cc:4121
#1  0x000000000165062d in Fill_process_list::operator() (this=0x7fffec5bb5f0, inspect_thd=0x67be360)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_show.cc:2591
#2  0x0000000000eef320 in Do_THD::operator() (this=0x7fffec5ba580, thd=0x67be360) at /mysqldata/percona-server-locks-detail-5.7.22/sql/mysqld_thd_manager.cc:46
#3  0x0000000000eefa0f in std::for_each<THD**, Do_THD> (__first=0x7fffec5ba5d0, __last=0x7fffec5ba5e8, __f=...)
    at /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algo.h:4200
#4  0x0000000000eeeecc in Global_THD_manager::do_for_all_thd_copy (this=0x3003340, func=0x7fffec5bb5f0)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/mysqld_thd_manager.cc:262
#5  0x0000000001637280 in fill_schema_processlist (thd=0x7ffedc008250, tables=0x7ffedc0016a8, cond=0x0)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_show.cc:2608
#6  0x000000000164ce11 in do_fill_table (thd=0x7ffedc008250, table_list=0x7ffedc0016a8, qep_tab=0x7ffedc015d40)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_show.cc:8791
#7  0x000000000164d31b in get_schema_tables_result (join=0x7ffedc015660, executed_place=PROCESSED_BY_JOIN_EXEC)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_show.cc:8921
#8  0x0000000001621761 in JOIN::prepare_result (this=0x7ffedc015660) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_select.cc:909
#9  0x000000000157e699 in JOIN::exec (this=0x7ffedc015660) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:124
#10 0x0000000001620327 in handle_query (thd=0x7ffedc008250, lex=0x7ffedc00a880, result=0x7ffedc0025c8, added_options=0, removed_options=0)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_select.cc:185
#11 0x00000000015d1f77 in execute_sqlcom_select (thd=0x7ffedc008250, all_tables=0x7ffedc0016a8) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:5445
#12 0x00000000015ca380 in mysql_execute_command (thd=0x7ffedc008250, first_level=true) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:2939
#13 0x00000000015d2fde in mysql_parse (thd=0x7ffedc008250, parser_state=0x7fffec5bd600) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:5901
#14 0x00000000015c6b72 in dispatch_command (thd=0x7ffedc008250, com_data=0x7fffec5bdd70, command=COM_QUERY)
    at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1490
#15 0x00000000015c58ff in do_command (thd=0x7ffedc008250) at /mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:1021
#16 0x000000000170e578 in handle_connection (arg=0x5f4fe40) at /mysqldata/percona-server-locks-detail-5.7.22/sql/conn_handler/connection_handler_per_thread.cc:312
#17 0x0000000001945538 in pfs_spawn_thread (arg=0x6809be0) at /mysqldata/percona-server-locks-detail-5.7.22/storage/perfschema/pfs.cc:2190
#18 0x00007ffff7bcfaa1 in start_thread () from /lib64/libpthread.so.0
#19 0x00007ffff6b37c4d in clone () from /lib64/libc.so.6

簡單記錄如下：

• Fill_process_list類 5.7
• fill_schema_processlist 函式 5.6

關於其中的Time來自如下處理，關於好像 -1 也是可能處出現的。

type_conversion_status Field_long::store(longlong nr, bool unsigned_val)
{
  ASSERT_COLUMN_MARKED_FOR_WRITE;
  type_conversion_status error= TYPE_OK;
  int32 res;
  if (unsigned_flag)
  {
    if (nr < 0 && !unsigned_val)
    {
      res=0;
      error= TYPE_WARN_OUT_OF_RANGE;
    }
    else if ((ulonglong) nr >= (1LL << 32))
    {
      res=(int32) (uint32) ~0L; //表示式-1
      error= TYPE_WARN_OUT_OF_RANGE;
    }
    else
      res=(int32) (uint32) nr;
  }
  else
  {
    if (nr < 0 && unsigned_val)
    {
      nr= ((longlong) INT_MAX32) + 1;           // Generate overflow
      error= TYPE_WARN_OUT_OF_RANGE;
    }
    if (nr < (longlong) INT_MIN32) 
    {
      res=(int32) INT_MIN32;
      error= TYPE_WARN_OUT_OF_RANGE;
    }
    else if (nr > (longlong) INT_MAX32)
    {
      res=(int32) INT_MAX32;
      error= TYPE_WARN_OUT_OF_RANGE;
    }
    else
      res=(int32) nr;
  }
  if (error)
    set_warning(Sql_condition::SL_WARNING, ER_WARN_DATA_OUT_OF_RANGE, 1);
#ifdef WORDS_BIGENDIAN
  if (table->s->db_low_byte_first)
  {
    int4store(ptr,res);
  }
  else
#endif
    longstore(ptr,res);
  return error;
}

三、不同現象的測試

我們看到這裡證明了上面的說法。他們來源不同。

作者微信：gp_22389860