The patch enables back constant subquery execution during
query optimization after it was disabled during the development
of MWL#89 (cost-based choice of IN-TO-EXISTS vs MATERIALIZATION).
The main idea is that constant subqueries are allowed to be executed
during optimization if their execution is not expensive.
The approach is as follows:
- Constant subqueries are recursively optimized in the beginning of
JOIN::optimize of the outer query. This is done by the new method
JOIN::optimize_constant_subqueries(). This is done so that the cost
of executing these queries can be estimated.
- Optimization of the outer query proceeds normally. During this phase
the optimizer may request execution of non-expensive constant subqueries.
Each place where the optimizer may potentially execute an expensive
expression is guarded with the predicate Item::is_expensive().
- The implementation of Item_subselect::is_expensive has been extended
to use the number of examined rows (estimated by the optimizer) as a
way to determine whether the subquery is expensive or not.
- The new system variable "expensive_subquery_limit" controls how many
examined rows are considered to be not expensive. The default is 100.
In addition, multiple changes were needed to make this solution work
in the light of the changes made by MWL#89. These changes were needed
to fix various crashes and wrong results, and legacy bugs discovered
during development.
Fixed failing tests in sys_vars as we have now stricter checking of setting of variables.
mysql-test/suite/sys_vars/r/innodb_adaptive_flushing_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_adaptive_hash_index_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_large_prefix_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_random_read_ahead_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_stats_on_metadata_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_strict_mode_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_support_xa_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/innodb_table_locks_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/rpl_semi_sync_master_enabled_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/r/rpl_semi_sync_slave_enabled_basic.result:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_adaptive_flushing_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_adaptive_hash_index_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_large_prefix_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_random_read_ahead_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_stats_on_metadata_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_strict_mode_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_support_xa_basic.test:
One can now only assign 0 or 1 to boolean variables
mysql-test/suite/sys_vars/t/innodb_table_locks_basic.test:
One can now only assign 0 or 1 to boolean variables
mysys/my_getsystime.c:
Merge + fixed bug that __NR_clock_gettime didn't work in 5.5
Make the slave options --replicate-* dynamic variables so that these
options can be changed dynamically while the server is running,
which enables users to modify replication filtering rules without
having to stop and restart the server.
This is accomplished by just requiring that the slave threads are
stopped when these options are set dynamically. Since filtering
rules are only used by the SQL slave thread, setting them while the
thread is not running avoids the need for locking.
MEMORY LEAK.
Background:
- There are caches for stored functions and stored procedures (SP-cache);
- There is no similar cache for events;
- Triggers are cached together with TABLE objects;
- Those SP-caches are per-session (i.e. specific to each session);
- A stored routine is represented by a sp_head-instance internally;
- SP-cache basically contains sp_head-objects of stored routines, which
have been executed in a session;
- sp_head-object is added into the SP-cache before the corresponding
stored routine is executed;
- SP-cache is flushed in the end of the session.
The problem was that SP-cache might grow without any limit. Although this
was not a pure memory leak (the SP-cache is flushed when session is closed),
this is still a problem, because the user might take much memory by
executing many stored routines.
The patch fixes this problem in the least-intrusive way. A soft limit
(similar to the size of table definition cache) is introduced. To represent
such limit the new runtime configuration parameter 'stored_program_cache'
is introduced. The value of this parameter is stored in the new global
variable stored_program_cache_size that used to control the size of SP-cache
to overflow.
The parameter 'stored_program_cache' limits number of cached routines for
each thread. It has the following min/default/max values given from support:
min = 256, default = 256, max = 512 * 1024.
Also it should be noted that this parameter limits the size of
each cache (for stored procedures and for stored functions) separately.
The SP-cache size is checked after top-level statement is parsed.
If SP-cache size exceeds the limit specified by parameter
'stored_program_cache' then SP-cache is flushed and memory allocated for
cache objects is freed. Such approach allows to flush cache safely
when there are dependencies among stored routines.
sql/mysqld.cc:
Added global variable stored_program_cache_size to store value of
configuration parameter 'stored-program-cache'.
sql/mysqld.h:
Added declaration of global variable stored_program_cache_size.
sql/sp_cache.cc:
Extended interface for sp_cache by adding helper routine
sp_cache_enforce_limit to control size of stored routines cache for
overflow. Also added method enforce_limit into class sp_cache that
implements control of cache size for overflow.
sql/sp_cache.h:
Extended interface for sp_cache by adding standalone routine
sp_cache_enforce_limit to control size of stored routines cache
for overflow.
sql/sql_parse.cc:
Added flush of sp_cache after processing of next sql-statement
received from a client.
sql/sql_prepare.cc:
Added flush of sp_cache after preparation/execution of next prepared
sql-statement received from a client.
sql/sys_vars.cc:
Added support for configuration parameter stored-program-cache.
and cryptic error 1126 message
The problem was that dlopen() related code was using just a subset
of the path normalization routines used in other places.
Fixed the expansion of the pre-dlopen() behavior for plugins and UDFs
to use a platform-dependent consistent encoding of the paths.
Fixed the error dlopen() error handling to take the correct error message
and strip off the trailing newline character(s).
Fixed tests to do a platform independent replace of directories and to
account for the traling slash.
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.
* rename all debugging related command-line options
and variables to start from "debug-", and made them all
OFF by default.
* replace "MySQL" with "MariaDB" in error messages
* "Cast ... converted ... integer to it's ... complement"
is now a note, not a warning
* @@query_cache_strip_comments now has a session scope,
not global.
Setting query_cache_size to larger values might fail depending on the memory
pressure being put on the system. This can be seen on pushbuild as the test
case query_cache_size_basic tries to allocate a +3GB query cache, which
succeeds in some machines and fails in others.
So this part of the code where the test case tries to allocate +3GB query cache has been
disabled for now to get the test running on pb2.
BY CACHING OR REDUCING CREATEEVENT CALLS".
5.5 versions of MySQL server performed worse than 5.1 versions
under single-connection workload in autocommit mode on Windows XP.
Part of this slowdown can be attributed to overhead associated
with constant creation/destruction of MDL_lock objects in the MDL
subsystem. The problem is that creation/destruction of these
objects causes creation and destruction of associated
synchronization primitives, which are expensive on Windows XP.
This patch tries to alleviate this problem by introducing a cache
of unused MDL_object_lock objects. Instead of destroying such
objects we put them into the cache and then reuse with a new
key when creation of a new object is requested.
To limit the size of this cache, a new --metadata-locks-cache-size
start-up parameter was introduced.
mysql-test/r/mysqld--help-notwin.result:
Updated test after adding --metadata-locks-cache-size
parameter.
mysql-test/r/mysqld--help-win.result:
Updated test after adding --metadata-locks-cache-size
parameter.
mysql-test/suite/sys_vars/r/metadata_locks_cache_size_basic.result:
Added test coverage for newly introduced --metadata_locks_cache_size
start-up parameter and corresponding global read-only variable.
mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic-master.opt:
Added test coverage for newly introduced --metadata_locks_cache_size
start-up parameter and corresponding global read-only variable.
mysql-test/suite/sys_vars/t/metadata_locks_cache_size_basic.test:
Added test coverage for newly introduced --metadata_locks_cache_size
start-up parameter and corresponding global read-only variable.
sql/mdl.cc:
Introduced caching of unused MDL_object_lock objects, in order to
avoid costs associated with constant creation and destruction of
such objects in single-connection workloads run in autocommit mode.
Such costs can be pretty high on systems where creation and
destruction of synchronization primitives require a system call
(e.g. Windows XP).
To implement this cache,a list of unused MDL_object_lock instances
was added to MDL_map object. Instead of being destroyed
MDL_object_lock instances are put into this list and re-used later
when creation of a new instance is required. Also added
MDL_lock::m_version counter to allow threads having outstanding
references to an MDL_object_lock instance to notice that it has
been moved to the unused objects list.
Added a global variable for a start-up parameter that limits
the size of the unused objects list.
Note that we don't cache MDL_scoped_lock objects since they
are supposed to be created only during execution of DDL
statements and therefore should not affect performance much.
sql/mdl.h:
Added a global variable for start-up parameter that limits the
size of the unused MDL_object_lock objects list and constant
for its default value.
sql/sql_plist.h:
Added I_P_List<>::pop_front() function.
sql/sys_vars.cc:
Introduced --metadata-locks-cache-size start-up parameter
for specifying size of the cache of unused MDL_object_lock
objects.
If we meet DB_TOO_MANY_CONCURRENT_TRXS during the execution tab_create_graph from row_create_table_for_mysql(), .ibd file for the table should be created already but was not deleted for the error handling.
rb:875 approved by Jimmy Yang
