Description:
read_buffer_size is listed as "dynamic system variables" at
http://dev.mysql.com/doc/mysql/en/Dynamic_System_Variables.html
and I'm sure global_system_variables.read_buff_size is updated with "SET GLOBAL
read_buffer_size=xxxx;". However, the another global variable
"my_default_record_cache_size" is not updated in this case while other global
variables like "myisam_max_temp_length" and "myisam_max_extra_temp_length"
are updated with "fix_myisam_max_extra_sort_file_size()" etc...
IMHO it's better to update my_default_record_cache_size, too, in case
global_system_variables.read_buff_size is updated dynamically (since this value
affects not only cachesize of IO_CACHE but the block size of Append_Block event
indirectly and so on, as you know...).
How to repeat:
The typical case may be like this:
$ mysql test
> LOAD DATA INFILE '/tmp/infile.txt' ...
> \q
$ mysqlbinlog ...
(snip)
# at 17903090
#041025 12:41:53 server id 1 log_pos 17903090
#Append_block: file_id: 2 block_len: 1048576
(snip)
(and then I wanted to reduce block_len of Append_block events without shutdown)
$ mysql test
> SET GLOBAL read_buffer_size=16384
> \q
$ mysql test
> LOAD DATA INFILE '/tmp/infile.txt' ...
> \q
$ mysqlbinlog ...
(snip)
# at 27403119
#041025 12:48:51 server id 1 log_pos 27403119
#Append_block: file_id: 3 block_len: 1048576
(snip)
(block_len still remains to be not 16K but 1M...)
Suggested fix:
something like this?
diff -u set_var.cc.bak set_var.cc [~/work/mysql-4.0.21/sql]
--- set_var.cc.bak Tue Sep 7 07:29:37 2004
+++ set_var.cc Mon Oct 25 12:32:00 2004
@@ -85,6 +85,7 @@
static void fix_key_buffer_size(THD *thd, enum_var_type type);
static void fix_myisam_max_extra_sort_file_size(THD *thd, enum_var_type type);
static void fix_myisam_max_sort_file_size(THD *thd, enum_var_type type);
+static void fix_read_buff_size(THD *thd, enum_var_type type);
static void fix_max_binlog_size(THD *thd, enum_var_type type);
static void fix_max_relay_log_size(THD *thd, enum_var_type type);
static void fix_max_connections(THD *thd, enum_var_type type);
@@ -200,8 +201,7 @@
&SV::net_retry_count,
fix_net_retry_count);
sys_var_thd_bool sys_new_mode("new", &SV::new_mode);
-sys_var_thd_ulong sys_read_buff_size("read_buffer_size",
- &SV::read_buff_size);
+sys_var_thd_ulong sys_read_buff_size("read_buffer_size", &SV::read_buff_size, fix_read_buff_siz
e);
sys_var_bool_ptr sys_readonly("read_only", &opt_readonly);
sys_var_thd_ulong sys_read_rnd_buff_size("read_rnd_buffer_size",
&SV::read_rnd_buff_size);
@@ -679,6 +679,13 @@
{
myisam_max_temp_length=
(my_off_t) global_system_variables.myisam_max_sort_file_size;
+}
+
+static void
+fix_read_buff_size(THD *thd, enum_var_type type)
+{
+ my_default_record_cache_size=
+ (my_off_t) global_system_variables.read_buff_size;
}
/*
