Checking for kill with thd_kill_level() or check_killed() runs apc
requests, which takes the LOCK_thd_kill mutex. But this is dangerous,
as checking for kill needs to be called while holding many different
mutexes, and can lead to cyclic mutex dependency and deadlock.
But running apc is only "best effort", so skip running the apc if the
LOCK_thd_kill is not available. The apc will then be run on next check
of kill signal.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
- Describe the lifetime of EXPLAIN data structures in
sql_explain.h:ExplainDataStructureLifetime.
- Make Item_field::set_field() call set_refers_to_temp_table()
when it refers to a temp. table.
- Introduce QT_DONT_ACCESS_TMP_TABLES flag for Item::print.
It directs Item_field::print to not try access its the
temp table.
- Introduce Explain_query::notify_tables_are_closed()
and call it right before the query closes its tables.
- Make Explain data stuctures' print_explain_json() methods
accept "no_tmp_tbl" parameter which means pass
QT_DONT_ACCESS_TMP_TABLES when printing items.
- Make Show_explain_request::call_in_target_thread() not call
set_current_thd(). This wasn't needed as the code inside
lex->print_explain() uses output->thd anyway. output->thd
refers to the SHOW command's THD object.
SHOW EXPLAIN/ANALYZE FORMAT=JSON tries to access items that have already been
freed by a call to free_items() during THD::cleanup_after_query().
The solution is to disallow APC calls including SHOW EXPLAIN/ANALYZE
just before the call to free_items().
LOCK_thd_data was used to protect both THD data and
ensure that the THD is not deleted while it was in use
This patch moves the THD delete protection to LOCK_thd_kill,
which already protects the THD for kill.
The benefits are:
- More well defined what LOCK_thd_data protects
- LOCK_thd_data usage is now much simpler and easier to verify
- Less chance of deadlocks in SHOW PROCESS LIST as there is less
chance of interactions between mutexes
- Remove not needed LOCK_thread_count from
thd_get_error_context_description()
- Fewer mutex taken for thd->awake()
Other things:
- Don't take mysys->var mutex in show processlist to check if thread
is kill marked
- thd->awake() now automatically takes the LOCK_thd_kill mutex
(Simplifies code)
- Apc uses LOCK_thd_kill instead of LOCK_thd_data
- Added sql/mariadb.h file that should be included first by files in sql
directory, if sql_plugin.h is not used (sql_plugin.h adds SHOW variables
that must be done before my_global.h is included)
- Removed a lot of include my_global.h from include files
- Removed include's of some files that my_global.h automatically includes
- Removed duplicated include's of my_sys.h
- Replaced include my_config.h with my_global.h
Moved Apc_target::destroy(), Apc_target::enable() and Apc_targe::disable()
definitions to my_apc.h so that they can be inlined.
Apc_targe::disable() now calls Apc_target::process_apc_requests() only if
there're APC requests. This saves one pthread_mutex_lock() call.
Overhead change:
Apc_target::disable 0.04% -> out of radar
Apc_target::enable 0.03% -> out of radar
Apc_target::process_apc_requests 0.02% -> out of radar
pthread_mutex_lock 0.43% -> 0.42%
pthread_mutex_unlock 0.26% -> 0.25%
- Fix asserts, make sure that mysql_delete() operates on
thd->apc_target correctly* in all kinds of special cases
* - correctly means that one must switch it OFF iff it
was switched ON.
- Added a few asserts to catch similar errors.
- Fix the year in Monty Program Ab copyrights in the new files.
- Fix permissions handling so that SHOW EXPLAIN's handling is the
same as SHOW PROCESSLIST's.
- Add Monty Program Ab copyright in new files
- Change Apc_target::make_apc_call() to accept a C++-style
functor (instead of C-style function + parameter)
- Implement new approach to testing (the DBUG_EXECUTE_IF variant)
- add an 'evalp' mysqltest command that is like 'eval' except that
it prints the original query.
- Fix select_describe() not to change join_tab[i]->type
- More tests
First code
- "Asynchronous procedure call" system
- new THD::check_killed() that serves APC request is called from within most important loops
- EXPLAIN code is now able to generate EXPLAIN output on-the-fly [incomplete]
Parts that are still missing:
- put THD::check_killed() call into every loop where we could spend significant amount of time
- Make sure EXPLAIN code works for group-by queries that replace JOIN::join_tab with make_simple_join()
and other such cases.
- User interface: what error code to use, where to get timeout settings from, etc.
