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Continuing on from Tutorial 2.

When reviewing the 2.1. C/C++ Coding Guidelines for MySQL, you will see that the MySQL Source uses within the C/C++ code DBUG (Fred Fish’s debug library). This is one of the 3rd party open source products that are documented in the Internals 1.4. The Open-source Directories.

You will also find some usage in the MySQL Manual E.3 The DBUG Package. So enough talk, how do you use this.

DBUG

You get the DBUG output by running a mysqld debug version with the argument –debug. The output for the SHOW AUTHORS commands is:

T@9190304: >dispatch_command
T@9190304: | >alloc_root
..
T@9190304: | query: SHOW AUTHORS
T@9190304: | >mysql_parse
T@9190304: | | >mysql_init_query
T@9190304: | | | >lex_start
T@9190304: | | | | >alloc_root
T@9190304: | | | | | enter: root: 0x9590b38
T@9190304: | | | | | exit: ptr: 0x95c1c70
T@9190304: | | | | <alloc_root
T@9190304: | | | <lex_start
T@9190304: | | | >mysql_reset_thd_for_next_command
T@9190304: | | | <mysql_reset_thd_for_next_command
T@9190304: | | <mysql_init_query
T@9190304: | | >Query_cache::send_result_to_client
T@9190304: | | <query_cache ::send_result_to_client
T@9190304: | | >mysql_execute_command
T@9190304: | | | >mysqld_show_authors
T@9190304: | | | | >alloc_root
T@9190304: | | | | | enter: root: 0x9590b38
T@9190304: | | | | | exit: ptr: 0x95c1c78
T@9190304: | | | | <alloc_root
...
T@9190304: | | | | >send_fields
T@9190304: | | | | | packet_header: Memory: 0x8c2480  Bytes: (4) 01 00 00 01
T@9190304: | | | | | >alloc_root
T@9190304: | | | | >Protocol::write
T@9190304: | | | | <protocol ::write
...
T@9190304: | | | | >send_eof
T@9190304: | | | | | packet_header: Memory: 0x8c2550  Bytes: (4) 05 00 00 51
T@9190304: | | | | | >net_flush
T@9190304: | | | | | | >vio_is_blocking
T@9190304: | | | | | | | exit: 0
T@9190304: | | | | | | <vio_is_blocking
T@9190304: | | | | | | >net_real_write
T@9190304: | | | | | | | >vio_write
T@9190304: | | | | | | | | enter: sd: 23, buf: 0x0x95b9bd0, size: 5107
T@9190304: | | | | | | | | exit: 5107
T@9190304: | | | | | | | <vio_write
T@9190304: | | | | | | <net_real_write
T@9190304: | | | | | <net_flush
T@9190304: | | | | | info: EOF sent, so no more error sending allowed
T@9190304: | | | | <send_eof
T@9190304: | | | <mysqld_show_authors
T@9190304: | | <mysql_execute_command
T@9190304: | | >query_cache_end_of_result
T@9190304: | | <query_cache_end_of_result
...
T@9190304: | <mysql_parse
T@9190304: | info: query ready
T@9190304: | >log_slow_statement
T@9190304: | <log_slow_statement
T@9190304: >dispatch_command

Using some of the debug options you get the following output with –debug=d,info,error,query,general,where:O,/tmp/mysqld.trace

create_new_thread: info: creating thread 3
create_new_thread: info: Thread created
?func: info: handle_one_connection called by thread 3
?func: info: New connection received on socket (23)
?func: info: Host: localhost
?func: info: vio_read returned -1,  errno: 11
thr_alarm: info: reschedule
process_alarm: info: sig: 14  active alarms: 1
?func: info: client_character_set: 8
check_user: info: Capabilities: 238213  packet_length: 16777216  Host: 'localhost'  Login user: 'rbradfor' Priv_user: ''  Using password: no Access: 0  db: '*none*'
send_ok: info: affected_rows: 0  id: 0  status: 2  warning_count: 0
send_ok: info: OK sent, so no more error sending allowed
do_command: info: vio_read returned -1,  errno: 11
thr_alarm: info: reschedule
process_alarm: info: sig: 14  active alarms: 1
do_command: info: Command on socket (23) = 3 (Query)
dispatch_command: query: SHOW AUTHORS
send_eof: info: EOF sent, so no more error sending allowed
dispatch_command: info: query ready
do_command: info: vio_read returned -1,  errno: 11
thr_alarm: info: reschedule
process_alarm: info: sig: 14  active alarms: 1
do_command: info: Command on socket (23) = 1 (Quit)
~THD(): info: freeing security context
end_thread: info: sending a broadcast
end_thread: info: unlocked thread_count mutex

I have found the following format good for comparing with the MySQL Source Code. —debug=d:N:F:L:O,/tmp/mysqld.trace

   49:   sql_parse.cc:  1536: do_command: info: Command on socket (23) = 3 (Query)
   50:     my_alloc.c:   172: alloc_root: enter: root: 0x9068b38
   51:     my_alloc.c:   219: alloc_root: exit: ptr: 0x9099c30
   52:   safemalloc.c:   128: _mymalloc: enter: Size: 16384
   53:   safemalloc.c:   197: _mymalloc: exit: ptr: 0x909cc80
   54:   safemalloc.c:   262: _myfree: enter: ptr: 0x9095bf8
   55:   sql_parse.cc:  1757: dispatch_command: query: SHOW AUTHORS
..
   88:    sql_show.cc:   385: mysqld_show_authors: packet_header: Memory: 0x940590  Bytes: (4)
..
  166:    protocol.cc:   385: send_eof: packet_header: Memory: 0x940550  Bytes: (4)
05 00 00 51
  167:    viosocket.c:   184: vio_is_blocking: exit: 0
  168:    viosocket.c:   105: vio_write: enter: sd: 23, buf: 0x0x9091bd0, size: 5107
  169:    viosocket.c:   117: vio_write: exit: 5107
  170:    protocol.cc:   342: send_eof: info: EOF sent, so no more error sending allowed
  171:     sql_lex.cc:   199: lex_end: enter: lex: 0x9068b58
  172:   sql_parse.cc:  1796: dispatch_command: info: query ready
  173:     my_alloc.c:   331: free_root: enter: root: 0x9068b38  flags: 1
  174:    viosocket.c:   184: vio_is_blocking: exit: 0
  175:    viosocket.c:    36: vio_read: enter: sd: 23, buf: 0x0x9091bd0, size: 4
  176:    viosocket.c:    49: vio_read: vio_error: Got error 11 during read
  177:    viosocket.c:    52: vio_read: exit: -1
  178:   sql_parse.cc:   809: do_command: info: vio_read returned -1,  errno: 11

  190:   sql_parse.cc:  1536: do_command: info: Command on socket (23) = 1 (Quit)
  191:     my_alloc.c:   331: free_root: enter: root: 0x9068b38  flags: 1
  192:      mysqld.cc:  1681: close_connection: enter: fd: socket (23)  error: ''
  193: sql_handler.cc:   628: mysql_ha_flush: enter: tables: (nil)  mode_flags: 0x02

This will make a lot more sense with my upcoming presentation where you will see clear use and interaction between source files such as sql_parse.cc & sql_show.cc.

For more information check out Making Trace Files