mirror of
https://github.com/MariaDB/server.git
synced 2025-11-28 17:36:30 +03:00
be8709eb7b
This task involves the implementation for the optimizer trace.
This feature produces a trace for any SELECT/UPDATE/DELETE/,
which contains information about decisions taken by the optimizer during
the optimization phase (choice of table access method, various costs,
transformations, etc). This feature would help to tell why some decisions were
taken by the optimizer and why some were rejected.
Trace is session-local, controlled by the @@optimizer_trace variable.
To enable optimizer trace we need to write:
set @@optimizer_trace variable= 'enabled=on';
To display the trace one can run:
SELECT trace FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
This task also involves:
MDEV-18489: Limit the memory used by the optimizer trace
introduces a switch optimizer_trace_max_mem_size which limits
the memory used by the optimizer trace. This was implemented by
Sergei Petrunia.
2008-02-29 Matthias Leich
=========================
1. The testsuite "funcs_1" is mostly intended for additional (compared
to the common regression tests stored in mysql-test/t) checks
of features (VIEWS, INFORMATION_SCHEMA, STORED PROCEDURES,...)
introduced with MySQL 5.0.
2. There were some extensions of this suite when new information_schema
views were introduced. But in most cases the tests for these views
were stored within the regression testsuite (mysql-test/t).
INFORMATION_SCHEMA views introduced with MySQL 5.1
==================================================
ENGINES (partially tested here)
EVENTS (partially tested here)
FILES
GLOBAL_STATUS
GLOBAL_VARIABLES
PARTITIONS
PLUGINS
PROCESSLIST (full tested here)
PROFILING
REFERENTIAL_CONSTRAINTS
SESSION_STATUS
SESSION_VARIABLES
3. Some hints for maintainers of this suite:
- SHOW TABLES ... LIKE '<pattern>'
does a case sensitive comparison between the tablename and
the pattern.
The names of the tables within the informationschema are in uppercase.
So please use something like
SHOW TABLES FOR information_schema LIKE 'TABLES'
when you intend to get the same non empty result set on OS with and
without case sensitive filesystems and default configuration.
- The name of the data dictionary is 'information_schema' (lowercase).
- Server on OS with filesystem with case sensitive filenames
(= The files 'abc' and 'Abc' can coexist.)
+ default configuration
Example of behaviour:
DROP DATABASE information_schema;
ERROR 42000: Access denied for user ... to database 'information_schema'
DROP DATABASE INFORMATION_SCHEMA;
ERROR 42000: Access denied for user ... to database 'INFORMATION_SCHEMA'
- Try to unify results by
--replace_result $engine_type <engine_to_be_tested>
if we could expect that the results for storage engine variants of a
test differ only in the engine names.
This makes future maintenance easier.
- Avoid the use of include/show_msg*.inc.
They produce "SQL" noise which annoys during server debugging and can be
easy replaced by "--echo ...".