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Allow for faster creation of threads in corner cases where pool would be overloaded with long non-yielding queries.

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To allow it, change minimum of thread_pool_stall_limit to be 10 milliseconds.

Also introduce a new parameter to oversubscribe a group . Number of threads running in  parallel would be higher than it normally should, leading to thrashing, but it may improving preemptiveness, which is useful for the described corner case.
This commit is contained in:
Vladislav Vaintroub
2011-12-31 05:24:11 +01:00
parent bb0a0c52a6
commit c216c9f0f0
7 changed files with 104 additions and 5 deletions
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47
mysql-test/suite/sys_vars/r/thread_pool_oversubscribe_basic.result Normal file
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@@ -0,0 +1,47 @@
SET @start_global_value = @@global.thread_pool_oversubscribe;
select @@global.thread_pool_oversubscribe;
@@global.thread_pool_oversubscribe
3
select @@session.thread_pool_oversubscribe;
ERROR HY000: Variable 'thread_pool_oversubscribe' is a GLOBAL variable
show global variables like 'thread_pool_oversubscribe';
Variable_name Value
thread_pool_oversubscribe 3
show session variables like 'thread_pool_oversubscribe';
Variable_name Value
thread_pool_oversubscribe 3
select * from information_schema.global_variables where variable_name='thread_pool_oversubscribe';
VARIABLE_NAME VARIABLE_VALUE
THREAD_POOL_OVERSUBSCRIBE 3
select * from information_schema.session_variables where variable_name='thread_pool_oversubscribe';
VARIABLE_NAME VARIABLE_VALUE
THREAD_POOL_OVERSUBSCRIBE 3
set global thread_pool_oversubscribe=60;
select @@global.thread_pool_oversubscribe;
@@global.thread_pool_oversubscribe
60
set global thread_pool_oversubscribe=1000;
select @@global.thread_pool_oversubscribe;
@@global.thread_pool_oversubscribe
1000
set session thread_pool_oversubscribe=1;
ERROR HY000: Variable 'thread_pool_oversubscribe' is a GLOBAL variable and should be set with SET GLOBAL
set global thread_pool_oversubscribe=1.1;
ERROR 42000: Incorrect argument type to variable 'thread_pool_oversubscribe'
set global thread_pool_oversubscribe=1e1;
ERROR 42000: Incorrect argument type to variable 'thread_pool_oversubscribe'
set global thread_pool_oversubscribe="foo";
ERROR 42000: Incorrect argument type to variable 'thread_pool_oversubscribe'
set global thread_pool_oversubscribe=-1;
Warnings:
Warning 1292 Truncated incorrect thread_pool_oversubscribe value: '-1'
select @@global.thread_pool_oversubscribe;
@@global.thread_pool_oversubscribe
1
set global thread_pool_oversubscribe=10000000000;
Warnings:
Warning 1292 Truncated incorrect thread_pool_oversubscribe value: '10000000000'
select @@global.thread_pool_oversubscribe;
@@global.thread_pool_oversubscribe
1000
set @@global.thread_pool_oversubscribe = @start_global_value;

2
mysql-test/suite/sys_vars/r/thread_pool_stall_limit_basic.result
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@@ -37,7 +37,7 @@ Warnings:
Warning 1292 Truncated incorrect thread_pool_stall_limit value: '-1'
select @@global.thread_pool_stall_limit;
@@global.thread_pool_stall_limit
60
10
set global thread_pool_stall_limit=10000000000;
Warnings:
Warning 1292 Truncated incorrect thread_pool_stall_limit value: '10000000000'

43
mysql-test/suite/sys_vars/t/thread_pool_oversubscribe_basic.test Normal file
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@@ -0,0 +1,43 @@
# uint global
--source include/not_windows.inc
--source include/not_embedded.inc
SET @start_global_value = @@global.thread_pool_oversubscribe;
#
# exists as global only
#
select @@global.thread_pool_oversubscribe;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
select @@session.thread_pool_oversubscribe;
show global variables like 'thread_pool_oversubscribe';
show session variables like 'thread_pool_oversubscribe';
select * from information_schema.global_variables where variable_name='thread_pool_oversubscribe';
select * from information_schema.session_variables where variable_name='thread_pool_oversubscribe';
#
# show that it's writable
#
set global thread_pool_oversubscribe=60;
select @@global.thread_pool_oversubscribe;
set global thread_pool_oversubscribe=1000;
select @@global.thread_pool_oversubscribe;
--error ER_GLOBAL_VARIABLE
set session thread_pool_oversubscribe=1;
#
# incorrect types
#
--error ER_WRONG_TYPE_FOR_VAR
set global thread_pool_oversubscribe=1.1;
--error ER_WRONG_TYPE_FOR_VAR
set global thread_pool_oversubscribe=1e1;
--error ER_WRONG_TYPE_FOR_VAR
set global thread_pool_oversubscribe="foo";
set global thread_pool_oversubscribe=-1;
select @@global.thread_pool_oversubscribe;
set global thread_pool_oversubscribe=10000000000;
select @@global.thread_pool_oversubscribe;
set @@global.thread_pool_oversubscribe = @start_global_value;

11
sql/sys_vars.cc
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@@ -2215,7 +2215,8 @@ static bool fix_threadpool_size(sys_var*, THD*, enum_var_type)
static bool fix_threadpool_stall_limit(sys_var*, THD*, enum_var_type)
{
tp_set_threadpool_stall_limit(threadpool_size);
tp_set_threadpool_stall_limit(threadpool_stall_limit);
return false;
}
#endif
@@ -2236,6 +2237,12 @@ static Sys_var_uint Sys_threadpool_idle_thread_timeout(
GLOBAL_VAR(threadpool_idle_timeout), CMD_LINE(REQUIRED_ARG),
VALID_RANGE(1, UINT_MAX), DEFAULT(60), BLOCK_SIZE(1)
);
static Sys_var_uint Sys_threadpool_oversubscribe(
"thread_pool_oversubscribe",
"How many additional active worker threads in a group are allowed.",
GLOBAL_VAR(threadpool_oversubscribe), CMD_LINE(REQUIRED_ARG),
VALID_RANGE(1, 1000), DEFAULT(3), BLOCK_SIZE(1)
);
static Sys_var_uint Sys_threadpool_size(
"thread_pool_size",
"Number of concurrently executing threads in the pool. "
@@ -2252,7 +2259,7 @@ static Sys_var_uint Sys_threadpool_stall_limit(
"If a worker thread is stalled, additional worker thread "
"may be created to handle remaining clients.",
GLOBAL_VAR(threadpool_stall_limit), CMD_LINE(REQUIRED_ARG),
VALID_RANGE(60, UINT_MAX), DEFAULT(500), BLOCK_SIZE(1),
VALID_RANGE(10, UINT_MAX), DEFAULT(500), BLOCK_SIZE(1),
NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
ON_UPDATE(fix_threadpool_stall_limit)
);

1
sql/threadpool.h
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@@ -7,6 +7,7 @@ extern uint threadpool_idle_timeout; /* Shutdown idle worker threads after this
extern uint threadpool_size; /* Number of parallel executing threads */
extern uint threadpool_stall_limit; /* time interval in 10 ms units for stall checks*/
extern uint threadpool_max_threads; /* Maximum threads in pool */
extern uint threadpool_oversubscribe; /* Maximum active threads in group */
/*
Threadpool statistics

1
sql/threadpool_common.cc
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@@ -23,6 +23,7 @@ uint threadpool_idle_timeout;
uint threadpool_size;
uint threadpool_stall_limit;
uint threadpool_max_threads;
uint threadpool_oversubscribe;
/*

4
sql/threadpool_unix.cc
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@@ -839,13 +839,13 @@ static void post_event(thread_group_t *thread_group, pool_event_t* ev)
/*
Check if pool is already overcommited.
This is used to prevent too many threads executing at the same time,
if the workload is not CPU bound.
*/
static bool too_many_threads(thread_group_t *thread_group)
{
return (thread_group->active_thread_count >= 4 && !thread_group->stalled);
return (thread_group->active_thread_count >= 1+(int)threadpool_oversubscribe
&& !thread_group->stalled);
}