• Davi Arnaut's avatar
    Bug#34043: Server loops excessively in _checkchunk() when safemalloc is enabled · 3143a4dc
    Davi Arnaut authored
    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.
    
    client/mysqldump.c:
      Pass my_free directly as its signature is compatible with the
      callback type -- which wasn't the case for free_table_ent.
    3143a4dc
db2i_file.h 12.3 KB