今天一个朋友问我sort_buffer/join_buffer/binlog_cache_size/read_rnd_buff_size 等线程相关参数是什么时候分配内存的。我就特意做了gdb调试，得出结论这些参数都是在需要的时候才分配的，并不是建立线程就分配了，这里只是简单的给出我的结论并且给出栈帧以备后面学习和调试。水平有限有误请共同讨论。

一、sort_buffer

  • 触发分配时机为需要内存排序的时候才按需分配
  • 断点位置Filesort_buffer::alloc_sort_buffer
  • 参数
static Sys_var_ulong Sys_sort_buffer("sort_buffer_size","Each thread that needs to do a sort allocates a buffer of this size",SESSION_VAR(sortbuff_size), CMD_LINE(REQUIRED_ARG),VALID_RANGE(MIN_SORT_MEMORY, ULONG_MAX), DEFAULT(DEFAULT_SORT_MEMORY),BLOCK_SIZE(1));
  • 栈帧如下
#0  Filesort_buffer::alloc_sort_buffer (this=0x7ffff0359550, num_records=1310, record_length=70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/filesort_utils.cc:103
#1  0x0000000000f59316 in Filesort_info::alloc_sort_buffer (this=0x7ffff0359550, num_records=1310, record_length=70)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_sort.h:509
#2  0x0000000000f50fc7 in filesort (thd=0x7fff2c000b70, filesort=0x7fff2caad6c0, sort_positions=false, examined_rows=0x7ffff03598a0, found_rows=0x7ffff0359898, returned_rows=0x7ffff0359890) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/filesort.cc:394
#3  0x0000000001562667 in create_sort_index (thd=0x7fff2c000b70, join=0x7fff2c007490, tab=0x7fff2caad3d0)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:3677
#4  0x000000000155f7af in QEP_TAB::sort_table (this=0x7fff2caad3d0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2602
#5  0x000000000155f197 in join_init_read_record (tab=0x7fff2caad3d0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2468
#6  0x000000000155c359 in sub_select (join=0x7fff2c007490, qep_tab=0x7fff2caad3d0, end_of_records=false)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271
#7  0x000000000155bcde in do_select (join=0x7fff2c007490) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944
#8  0x0000000001559bb4 in JOIN::exec (this=0x7fff2c007490) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199
#9  0x00000000015f9e7e in handle_query (thd=0x7fff2c000b70, lex=0x7fff2c003150, result=0x7fff2c006f58, added_options=0, removed_options=0)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:184
#10 0x00000000015accdd in execute_sqlcom_select (thd=0x7fff2c000b70, all_tables=0x7fff2c0067f0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5391
#11 0x00000000015a52f8 in mysql_execute_command (thd=0x7fff2c000b70, first_level=true) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:2889
#12 0x00000000015adcae in mysql_parse (thd=0x7fff2c000b70, parser_state=0x7ffff035b600) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5836
#13 0x00000000015a1b6d in dispatch_command (thd=0x7fff2c000b70, com_data=0x7ffff035bd70, command=COM_QUERY)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1447
#14 0x00000000015a099e in do_command (thd=0x7fff2c000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1010
#15 0x00000000016e28f0 in handle_connection (arg=0x68d6da0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:312
#16 0x0000000001d7a514 in pfs_spawn_thread (arg=0x38474d0) at /root/mysql5.7.14/percona-server-5.7.14-7/storage/perfschema/pfs.cc:2188
#17 0x0000003f74807aa1 in start_thread () from /lib64/libpthread.so

二、join_buffer

  • 触发分配时机为进行BNL join 的时候才进行分配
  • 断点位置JOIN_CACHE::alloc_buffer
  • 参数
static Sys_var_ulong Sys_join_buffer_size("join_buffer_size","The size of the buffer that is used for full joins",SESSION_VAR(join_buff_size), CMD_LINE(REQUIRED_ARG),VALID_RANGE(128, ULONG_MAX), DEFAULT(256 * 1024), BLOCK_SIZE(128));
  • 栈帧如下
#0  JOIN_CACHE::alloc_buffer (this=0x7fff2caaeda8) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_join_buffer.cc:456
#1  0x00000000017d80ec in JOIN_CACHE_BNL::init (this=0x7fff2caaeda8) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_join_buffer.cc:684
#2  0x00000000015fe9e8 in QEP_TAB::init_join_cache (this=0x7fff2caaec30, join_tab=0x7fff2caae268) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:2060
#3  0x00000000015feede in make_join_readinfo (join=0x7fff2caadc38, no_jbuf_after=4294967295) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:2173
#4  0x000000000157f635 in JOIN::optimize (this=0x7fff2caadc38) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_optimizer.cc:683
#5  0x00000000015fb6f5 in st_select_lex::optimize (this=0x7fff2c005a90, thd=0x7fff2c000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:1009
#6  0x00000000015f9e08 in handle_query (thd=0x7fff2c000b70, lex=0x7fff2c003150, result=0x7fff2c0079b0, added_options=0, removed_options=0)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:164
#7  0x00000000015acbb1 in execute_sqlcom_select (thd=0x7fff2c000b70, all_tables=0x7fff2c006c28) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5376
#8  0x00000000015a52f8 in mysql_execute_command (thd=0x7fff2c000b70, first_level=true) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:2889
#9  0x00000000015adcae in mysql_parse (thd=0x7fff2c000b70, parser_state=0x7ffff035b600) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5836
#10 0x00000000015a1b6d in dispatch_command (thd=0x7fff2c000b70, com_data=0x7ffff035bd70, command=COM_QUERY)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1447
#11 0x00000000015a099e in do_command (thd=0x7fff2c000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1010
#12 0x00000000016e28f0 in handle_connection (arg=0x68d6da0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:312
#13 0x0000000001d7a514 in pfs_spawn_thread (arg=0x38474d0) at /root/mysql5.7.14/percona-server-5.7.14-7/storage/perfschema/pfs.cc:2188
#14 0x0000003f74807aa1 in start_thread () from /lib64/libpthread.so.0
#15 0x0000003f740e8bcd in clone () from /lib64/libc.so.6

三、binlog_cache_size

  • 触发分配为在进行事物处理的时候才进行分配
  • 断点位置 init_io_cache_ext
  • 参数
static Sys_var_ulong Sys_binlog_cache_size("binlog_cache_size", "The size of the transactional cache for ""updates to transactional engines for the binary log. ""If you often use transactions containing many statements, ""you can increase this to get more performance",GLOBAL_VAR(binlog_cache_size),CMD_LINE(REQUIRED_ARG),VALID_RANGE(IO_SIZE, ULONG_MAX), DEFAULT(32768), BLOCK_SIZE(IO_SIZE),NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),ON_UPDATE(fix_binlog_cache_size));
  • 栈帧如下
#0  init_io_cache_ext (info=0x7fff2402c998, file=-1, cachesize=32768, type=WRITE_CACHE, seek_offset=0, use_async_io=0 '\000', cache_myflags=20, file_key=10)at /root/mysql5.7.14/percona-server-5.7.14-7/mysys/mf_iocache.c:154
#1  0x00000000018c8a68 in init_io_cache (info=0x7fff2402c998, file=-1, cachesize=32768, type=WRITE_CACHE, seek_offset=0, use_async_io=0 '\000', cache_myflags=20)at /root/mysql5.7.14/percona-server-5.7.14-7/mysys/mf_iocache.c:299
#2  0x00000000018c6ab6 in open_cached_file (cache=0x7fff2402c998, dir=0x2f9ed70 "/root/mysql5.7.14/percona-server-5.7.14-7/mysql-test/var/tmp/mysqld.1", prefix=0x2275fce "ML", cache_size=32768, cache_myflags=16) at /root/mysql5.7.14/percona-server-5.7.14-7/mysys/mf_cache.c:60
#3  0x00000000018598d2 in THD::binlog_setup_trx_data (this=0x7fff24000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/binlog.cc:9641
#4  0x0000000001859bd3 in binlog_start_trans_and_stmt (thd=0x7fff24000b70, start_event=0x7ffff02d7350) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/binlog.cc:9742
#5  0x0000000001859fc6 in THD::binlog_write_table_map (this=0x7fff24000b70, table=0x7fff2404ef00, is_transactional=true, binlog_rows_query=false)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/binlog.cc:9835
#6  0x0000000000f7299f in write_locked_table_maps (thd=0x7fff24000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:8019
#7  0x0000000000f72bf6 in binlog_log_row (table=0x7fff2404ef00, before_record=0x7fff2404fe20 "\375\001", after_record=0x0, log_func=0xf77f7d <Delete_rows_log_event::binlog_row_logging_function(THD*, TABLE*, bool, uchar const*, uchar const*)>)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:8089
#8  0x0000000000f73c39 in handler::ha_delete_row (this=0x7fff2404f8e0, buf=0x7fff2404fe20 "\375\001") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:8308
#9  0x00000000017c5451 in Sql_cmd_delete::mysql_delete (this=0x7fff240069c0, thd=0x7fff24000b70, limit=18446744073709551615)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_delete.cc:471
#10 0x00000000017c83da in Sql_cmd_delete::execute (this=0x7fff240069c0, thd=0x7fff24000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_delete.cc:1389
#11 0x00000000015a77ec in mysql_execute_command (thd=0x7fff24000b70, first_level=true) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:3729
#12 0x00000000015adcae in mysql_parse (thd=0x7fff24000b70, parser_state=0x7ffff02d9600) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5836
#13 0x00000000015a1b6d in dispatch_command (thd=0x7fff24000b70, com_data=0x7ffff02d9d70, command=COM_QUERY)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1447
#14 0x00000000015a099e in do_command (thd=0x7fff24000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1010
#15 0x00000000016e28f0 in handle_connection (arg=0x68e2320) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:312
#16 0x0000000001d7a514 in pfs_spawn_thread (arg=0x38474d0) at /root/mysql5.7.14/percona-server-5.7.14-7/storage/perfschema/pfs.cc:2188
#17 0x0000003f74807aa1 in start_thread () from /lib64/libpthread.so.0
#18 0x0000003f740e8bcd in clone () from /lib64/libc.so.6

四、read_rnd_buff_size

  • 触发为做MRR优化为执行语句需要使用缓存的时候才分配
  • 断点QUICK_RANGE_SELECT::reset
  • 参数
static Sys_var_ulong Sys_read_rnd_buff_size("read_rnd_buffer_size","When reading rows in sorted order after a sort, the rows are read ""through this buffer to avoid a disk seeks",SESSION_VAR(read_rnd_buff_size), CMD_LINE(REQUIRED_ARG),VALID_RANGE(1, INT_MAX32), DEFAULT(256*1024), BLOCK_SIZE(1));
  • 栈帧如下
#0  QUICK_RANGE_SELECT::reset (this=0x7fff24083c00) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/opt_range.cc:10958
#1  0x000000000155f1e1 in join_init_read_record (tab=0x7fff24051798) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2471
#2  0x000000000155c359 in sub_select (join=0x7fff240511b0, qep_tab=0x7fff24051798, end_of_records=false)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271
#3  0x000000000155bcde in do_select (join=0x7fff240511b0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944
#4  0x0000000001559bb4 in JOIN::exec (this=0x7fff240511b0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199
#5  0x00000000015f9e7e in handle_query (thd=0x7fff24000b70, lex=0x7fff24003150, result=0x7fff240072f0, added_options=0, removed_options=0)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_select.cc:184
#6  0x00000000015accdd in execute_sqlcom_select (thd=0x7fff24000b70, all_tables=0x7fff240069e0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5391
#7  0x00000000015a52f8 in mysql_execute_command (thd=0x7fff24000b70, first_level=true) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:2889
#8  0x00000000015adcae in mysql_parse (thd=0x7fff24000b70, parser_state=0x7ffff02d9600) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:5836
#9  0x00000000015a1b6d in dispatch_command (thd=0x7fff24000b70, com_data=0x7ffff02d9d70, command=COM_QUERY)at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1447
#10 0x00000000015a099e in do_command (thd=0x7fff24000b70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_parse.cc:1010
#11 0x00000000016e28f0 in handle_connection (arg=0x68e2320) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/conn_handler/connection_handler_per_thread.cc:312
#12 0x0000000001d7a514 in pfs_spawn_thread (arg=0x38474d0) at /root/mysql5.7.14/percona-server-5.7.14-7/storage/perfschema/pfs.cc:2188
#13 0x0000003f74807aa1 in start_thread () from /lib64/libpthread.so.0
#14 0x0000003f740e8bcd in clone () from /lib64/libc.so.6

仅此作为备忘记录
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