The "is it my own thread" check compared the login user name
(Security_context::user) and ignored the host, so u1@localhost could see
and kill threads of u1@'127.0.0.1'.
Compare the authenticated account instead:
* all comparisons are done in sctx->is_priv_user() now
* change user_matches() to priv_user_matches(), which uses is_priv_user()
* use it in KILL, KILL USER, SHOW PROCESSLIST, I_S.PROCESSLIST,
COM_PROCESS_INFO and SHOW EXPLAIN/ANALYZE FOR.
* all the remaining places use is_priv_user() directly instead
of doing strcmp: SHOW GRANTS, SHOW CREATE PROCEDURE, I_S.VIEWS,
the DEFINER clause, optimizer trace and change_security_context().
Assisted-by: Claude:claude-5-opus
Optimizer trace is disabled by default, yet init() was out of line, so
every statement paid a call plus a full prologue/epilogue only to test
FLAG_ENABLED and return.
Move the FLAG_ENABLED test into an inline init() so the disabled path
collapses to a flag load and a predicted-not-taken branch. The enabled
path setup stays out of line in the new init_traceable(). traceable is
left to the constructor and only asserted, not re-stored, in init(), so
no store lands on the disabled hot path. Behaviour and the init()
signature are unchanged.
The expanded_query field in optimizer trace could produce invalid JSON when
queries contained special characters. Use st_append_escaped() to properly
handle quotes, backslashes and other special characters in the output.
If st_append_escaped() fails, emit an error message in the expanded_query.
Example:
Before: "expanded_query": "select length('a') AS `LENGTH("a")`"
After: "expanded_query": "select length('a') AS `LENGTH(\"a\")`"
The output is now properly escaped and valid JSON while maintaining
readability.
Added test cases to mysql-test/main/opt_trace.test to verify the fix.
All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license
In mysql_execute_command(), move optimizer trace initialization to be
after run_set_statement_if_requested() call.
Unfortunately, mysql_execute_command() code uses "goto error" a lot, and
this means optimizer trace code cannot use RAII objects. Work this around
by:
- Make Opt_trace_start a non-RAII object, add init() method.
- Move the code that writes the top-level object and array into
Opt_trace_start::init().
- Print the rowid filters that are available for use with each table.
- Make print_best_access_for_table() print which filter it has picked.
- Make best_access_path() print the filter for considered ref accesses.
- Move testing of my_writer to inline functions to avoid calls
- Made more functions inline. Especially thd->thread_started()
is now very optimized!
- Moved Opt_trace_stmt classe to opt_trace_context.h to get critical
functions inline
- Added unlikely() to optimize for not having optimizer trace enabled
- Made THD::trace_started() inline
- Added 'if (trace_enabled())' around some potentially expensive code
(not many found)
- Added ASSERT's to ensure we don't call expensive optimizer trace calls
if optimizer trace is not enabled
- Added length to Json_writer functions to speed up buffer writes
when optimizer trace is enabled.
- Changed LEX_CSTRING argument handling to not send full struct to writer
function on_add_str() functions now trusts length arguments
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.
