Essentially, the problem is that safemalloc is excruciatingly
slow as it checks all allocated blocks for overrun at each
memory management primitive, yielding a almost exponential
slowdown for the memory management functions (malloc, realloc,
free). The overrun check basically consists of verifying some
bytes of a block for certain magic keys, which catches some
simple forms of overrun. Another minor problem is violation
of aliasing rules and that its own internal list of blocks
is prone to corruption.
Another issue with safemalloc is rather the maintenance cost
as the tool has a significant impact on the server code.
Given the magnitude of memory debuggers available nowadays,
especially those that are provided with the platform malloc
implementation, maintenance of a in-house and largely obsolete
memory debugger becomes a burden that is not worth the effort
due to its slowness and lack of support for detecting more
common forms of heap corruption.
Since there are third-party tools that can provide the same
functionality at a lower or comparable performance cost, the
solution is to simply remove safemalloc. Third-party tools
can provide the same functionality at a lower or comparable
performance cost.
The removal of safemalloc also allows a simplification of the
malloc wrappers, removing quite a bit of kludge: redefinition
of my_malloc, my_free and the removal of the unused second
argument of my_free. Since free() always check whether the
supplied pointer is null, redudant checks are also removed.
Also, this patch adds unit testing for my_malloc and moves
my_realloc implementation into the same file as the other
memory allocation primitives.
Several problems addressed:
1. The maximum value for --open_files_limit on non-windows boxes
is now raised to UINT_MAX (the maximum possible without significant
changes in the code). The maximum value on windows is kept to be
2048 due to a known limitation (bug 24509).
2. mysqld_safe now supports --open_files_limit=xx in addition to
--open-files-limit=xx
3. mysqld_safe always passes through --open[_-]files[_-]limit
to the underlying mysqld. It used to pass it through only if it
the user running the script has access to the root directory or
there was an --user argument specified.
4. Fixed a prototype in my_file.c to match its counterpart in
the other #ifdef branch.
Bug#24509 - 2048 file descriptor limit on windows needs increasing, also
WL#3049 - improved Windows I/O
The patch replaces the use of the POSIX I/O interfaces in mysys on Windows with
the Win32 API calls (CreateFile, WriteFile, etc). The Windows HANDLE for the open
file is stored in the my_file_info struct, along with a flag for append mode
because the Windows API does not support opening files in append mode in all cases)
The default max open files has been increased to 16384 and can be increased further
by setting --max-open-files=<value> during the server start.
Another major change in this patch that almost all Windows specific file IO code
has been moved to a new file my_winfile.c, greatly reducing the amount of code
in #ifdef blocks within mysys, thus improving readability.
Minor enhancements:
- my_(f)stat() is changed to use __stati64 structure with 64 file size
and timestamps. It will return correct file size now (C runtime implementation
used to report outdated information)
- my_lock on Windows is prepared to handle additional timeout parameter
- after review : changed __WIN__ to _WIN32 in the new and changed code.
This ensures that my_file_info takes this the max number of files into account and one can now use --open-files-limit on windows to increase number of used files up to 2048
