1. The PERSISTENT FOR clause of the ANALYZE command overrides
the setting of the system variable use_stat_tables:
with this clause ANALYZE unconditionally collects persistent
statistics.
2. ANALYZE collects persistent statistics only for tables of
the USER category. So it never collects persistent statistics
for system tables.
n_child_sum_items kept increasing.
Since it is used for calculating the size of ref_pointer_array,
we will allocate larger and larger chunks of memory, until we hit some
operating system limit.
The memory is free()d at disconnect, but is most likely *not*
returned to the operating system.
Documentation of the feature can be found at: http://kb.askmonty.org/en/multi-source-replication/
This code is based on code from Taobao, developed by Plinux
BUILD/SETUP.sh:
Added -Wno-invalid-offsetof to get rid of warning of offsetof() on C++ class (safe in the contex we use it)
client/mysqltest.cc:
Added support for error names starting with 'W'
Added connection_name support to --sync_with_master
cmake/maintainer.cmake:
Added -Wno-invalid-offsetof to get rid of warning of offsetof() on C++ class (safe in the contex we use it)
mysql-test/r/mysqltest.result:
Updated results
mysql-test/r/parser.result:
Updated results
mysql-test/suite/multi_source/my.cnf:
Setup of multi-master tests
mysql-test/suite/multi_source/simple.result:
Simple basic test of multi-source functionality
mysql-test/suite/multi_source/simple.test:
Simple basic test of multi-source functionality
mysql-test/suite/multi_source/syntax.result:
Test of multi-source syntax
mysql-test/suite/multi_source/syntax.test:
Test of multi-source syntax
mysql-test/suite/rpl/r/rpl_rotate_logs.result:
Updated results because of new error messages
mysql-test/t/parser.test:
Updated test as master_pos_wait() now takes more arguments than before
sql/event_scheduler.cc:
No reason to initialize slave_thread (it's guaranteed to be zero here)
sql/item_create.cc:
Added connection_name argument to master_pos_wait()
Simplified code
sql/item_func.cc:
Added connection_name argument to master_pos_wait()
sql/item_func.h:
Added connection_name argument to master_pos_wait()
sql/log.cc:
Added tag "Master 'connection_name'" to slave errors that has a connection name.
sql/mysqld.cc:
Added variable mysqld_server_initialized so that other functions can test if server is fully initialized.
Free all slave data in one place (fewer ifdef's)
Removed not needed call to close_active_mi()
Initialize slaves() later in startup to ensure that everthing is really initialized when slaves start.
Made status variable slave_running multi-source safe
sql/mysqld.h:
Added mysqld_server_initialized
sql/rpl_mi.cc:
Store connection name and cmp_connection_name (only used for show full slave status) in Master_info
Added code for Master_info_index, which handles storage of multi-master information
Don't write the empty "" connection_name to multi-master.info file. This is handled by the original code.
sql/rpl_mi.h:
Added connection_name and Master_info_index
sql/rpl_rli.cc:
Added connection_name to relay log files.
sql/rpl_rli.h:
Fixed type of slave_skip_counter as we now access it directly in sys_vars.cc, so it must be uint
sql/share/errmsg-utf8.txt:
Added new error messages needed for multi-source
Added multi-source name to error ER_MASTER_INFO and WARN_NO_MASTER_INFO
sql/slave.cc:
Moved things a bit around to make it easier to handle error conditions.
Create a global master_info_index and add the "" connection to it
Ensure that new Master_info doesn't fail.
Don't call terminate_slave_threads(active_mi..) on end_slave() as this is now done automaticly when deleting master_info_index.
Delete not needed function close_active_mi(). One can achive same thing by calling end_slave().
Added support for SHOW FULL SLAVE STATUS (show status for all master connections with connection_name as first column)
sql/slave.h:
Added new prototypes
sql/sql_base.cc:
More DBUG_PRINT
sql/sql_class.cc:
Reset thd->connection_name and thd-->default_master_connection
sql/sql_class.h:
Added thd->connection_name and thd-->default_master_connection
Added slave_skip_count to variables to make changing the @@sql_slave_skip_count variable thread safe
sql/sql_const.h:
Added MAX_CONNECTION_NAME
sql/sql_lex.cc:
Reset 'lex->verbose' (to simplify some sql_yacc.yy code)
sql/sql_lex.h:
Added connection_name
sql/sql_parse.cc:
Added support for connection_name to all SLAVE commands.
- Instead of using active_mi, we now get the current Master_info from master_info_index.
- Create new replication threads with CHANGE MASTER
- Added support for show_all_master_info()
sql/sql_reload.cc:
Made reset/full slave use master_info_index->get_master_info() instead of active_mi.
If one uses 'RESET SLAVE "connection_name" all' the connection is removed from master_info_index.
sql/sql_repl.cc:
sql_slave_skip_counter is moved to thd->variables to make it thread safe and fix some bugs with it
Add connection name to relay log files.
Added connection name to errors.
Added some logging for multi-master if log_warnings > 1
stop_slave():
- Don't check if thd is set. It's guaranteed to always be set.
change_master():
- Check for duplicate connection names in change_master()
- Check for wrong arguments first in file (to simplify error handling)
- Register new connections in master_info_index
sql/sql_yacc.yy:
Added optional connection_name to a all relevant master/slave commands
sql/strfunc.cc:
my_global.h shoud always be included first.
sql/sys_vars.cc:
Added variable default_master_connection
Made variable sql_slave_skip_counter multi-source safe
sql/sys_vars.h:
Added Sys_var_session_lexstring (needed for default_master_connection)
Added Sys_var_multi_source_uint (needed for sql_slave_skip_counter).
two tests still fail:
main.innodb_icp and main.range_vs_index_merge_innodb
call records_in_range() with both range ends being open
(which triggers an assert)
- Correct the way SHOW EXPLAIN code calculates 'need_order' parameter
for JOIN::print_explain().
The calculation is still an approximation (see MDEV entry for details) (even EXPLAIN itself
is wrong in certain cases), but now it's a better approximation than before.
- Make SHOW EXPLAIN code take into account that st_select_lex object without joins can be
a full-featured SELECTs which were already executed and cleaned up.
- Fixed code that was not ready for a major version number > 9
- Fixed test cases that assumed max major version number could be 9
Updated version number for depricated options (will be removed in a later commit)
VERSION:
Version number 10.0.0
client/mysqlbinlog.cc:
Added support for major version numbers > 9
cmake/mysql_version.cmake:
Added support for version numbers that is 0
mysql-test/r/comments.result:
Modified test to handle version number 100000
mysql-test/r/func_system.result:
Modified test to handle version number 100000
mysql-test/r/log_state.result:
Updated depricated error message
mysql-test/r/sp.result:
Modified test to handle version number 100000
mysql-test/r/subselect4.result:
Updated depricated error message
mysql-test/r/variables.result:
Updated depricated error message
mysql-test/suite/rpl/r/rpl_conditional_comments.result:
Modified test to handle version number 100000
mysql-test/suite/rpl/r/rpl_loaddatalocal.result:
Modified test to handle version number 100000
mysql-test/suite/rpl/t/rpl_conditional_comments.test:
Modified test to handle version number 100000
mysql-test/suite/rpl/t/rpl_loaddatalocal.test:
Modified test to handle version number 100000
mysql-test/suite/sys_vars/r/debug_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/engine_condition_pushdown_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/log_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/log_slow_queries_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/multi_range_count_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/rpl_recovery_rank_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_big_selects_func.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_max_join_size_basic.result:
Updated depricated error message
mysql-test/suite/sys_vars/r/sql_max_join_size_func.result:
Updated depricated error message
mysql-test/t/comments.test:
Modified test to handle version number 100000
mysql-test/t/file_contents.test:
Modified test to handle version number 100000
mysql-test/t/func_system.test:
Modified test to handle version number 100000
mysql-test/t/parser_not_embedded.test:
Modified test to handle version number 100000
mysql-test/t/sp.test:
Modified test to handle version number 100000
sql/mysqld.cc:
Updated version number for depricated options (will be removed in a later commit)
sql/slave.cc:
Modified test to handle version number 100000
Better error messages
sql/sql_lex.cc:
Modified test to handle version number 100000 in comment syntax
sql/sys_vars.cc:
Updated version number for depricated options (will be removed in a later commit)
Analysis:
The fix for lp:944706 introduces early subquery optimization.
While a subquery is being optimized some of its predicates may be
removed. In the test case, the EXISTS subquery is constant, and is
evaluated to TRUE. As a result the whole OR is TRUE, and thus the
correlated condition "b = alias1.b" is optimized away. The subquery
becomes non-correlated.
The subquery cache is designed to work only for correlated subqueries.
If constant subquery optimization is disallowed, then the constant
subquery is not evaluated, the subquery remains correlated, and its
execution is cached. As a result execution is fast.
However, when the constant subquery was optimized away, it was neither
cached by the subquery cache, nor it was cached by the internal subquery
caching. The latter was due to the fact that the subquery still appeared
as correlated to the subselect_XYZ_engine::exec methods, and they
re-executed the subquery on each call to Item_subselect::exec.
Solution:
The solution is to update the correlated status of the subquery after it has
been optimized. This status consists of:
- st_select_lex::is_correlated
- Item_subselect::is_correlated
- SELECT_LEX::uncacheable
- SELECT_LEX_UNIT::uncacheable
The status is updated by st_select_lex::update_correlated_cache(), and its
caller st_select_lex::optimize_unflattened_subqueries. The solution relies
on the fact that the optimizer already called
st_select_lex::update_used_tables() for each subquery. This allows to
efficiently update the correlated status of each subquery without walking
the whole subquery tree.
Notice that his patch is an improvement over MySQL 5.6 and older, where
subqueries are not pre-optimized, and the above analysis is not possible.
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.
- It turns out, there is a case where the join is degenerate, but
join->table_count!= && join->tables_list!=NULL. Need to also check
if join->zero_result_cause!=NULL, too.
- There is a slight problem: The code sets
zero_result_cause= "no matching row in const table"
when NOT running EXPLAIN. The result is that SHOW EXPLAIN will show this line while
regular EXPLAIN will not.
Make SHOW EXPLAIN work for queries that do "Using temporary" and/or "Using filesort"
- Patch#1: Don't lose "Using temporary/filesort" in the SHOW EXPLAIN output.
Analysis:
The reason for the wrong result is the interaction between constant
optimization (in this case 1-row table) and subquery optimization.
- First the outer query is optimized, and 'make_join_statistics' finds that
table t2 has one row, reads that row, and marks the whole table as constant.
This also means that all fields of t2 are constant.
- Next, we optimize the subquery in the end of the outer 'make_join_statistics'.
The field 'f2' is considered constant, with value '3'. The subquery predicate
is rewritten as the constant TRUE.
- The outer query execution detects early that the whole query result is empty
and calls 'return_zero_rows'. Since the query is with implicit grouping, we
have to produce one row with special values for the aggregates (depending on
each aggregate function), and NULL values for all non-aggregate fields. This
function calls 'no_rows_in_result' to set each aggregate function to the
default value when it aggregates over an empty result, and then calls
'send_data', which in turn evaluates each Item in the SELECT list.
- When evaluation reaches the subquery predicate, it executes the subquery
with field 'f2' having a constant value '3', and the subquery produces the
incorrect result '7'.
Solution:
Implement Item::no_rows_in_result for all subquery predicates. In order to
make this work, it is also needed to make all val_* methods of all subquery
predicates respect the Item_subselect::forced_const flag. Otherwise subqueries
are executed anyways, and override the default value set by no_rows_in_result
with whatever result is produced from the subquery evaluation.
