How to get memory size used for a query in mysql?

Question

THe reason I am asking this question is that I want to make sure if some of my queries will use more memory than that of query_cache_limit. Some people suggusted using 'show table status like 'table_name'. I think it is not relevant to this question. Thanks.

Answer 1

The size of the result set is not available in stock MySQL.

Percona Server does support this information, by adding a field to its extended slow-query log format. Look in the "Bytes_sent" field in this log.

See http://www.percona.com/doc/percona-server/5.5/diagnostics/slow_extended_55.html#memory-footprint

Answer 2

note this is not for the faint of heart. and do it on another box, not production !

stop mysql and start it under the view of valgrind.

do your thing for a while. for instance run a quick php that uses your routine/query.

maybe capture 20 seconds of data usage at most.

then stop mysql via same stop below.

then examine the log file in the /tmp dir ... examine data by timestamps

service mysql stop
apt-get install valgrind
valgrind --tool=massif --massif-out-file=/tmp/massif.out /etc/init.d/mysql start



    #-----------
    snapshot=32
    #-----------
    time=217073
    mem_heap_B=1140
    mem_heap_extra_B=324
    mem_stacks_B=0
    heap_tree=empty
    #-----------
    snapshot=33
    #-----------
    time=226099
    mem_heap_B=1156
    mem_heap_extra_B=332
    mem_stacks_B=0
    heap_tree=detailed
    n3: 1156 (heap allocation functions) malloc/new/new[], --alloc-fns, etc.
     n5: 944 0x40AA47: ??? (in /bin/dash)
      n3: 832 0x41184C: ??? (in /bin/dash)
       n1: 704 0x4120F5: ??? (in /bin/dash)
        n1: 704 0x4020E4: ??? (in /bin/dash)
         n0: 704 0x4E4E76B: (below main) (libc-start.c:226)
       n1: 96 0x411EC0: ??? (in /bin/dash)
        n1: 96 0x4048E3: ??? (in /bin/dash)
         n1: 96 0x403BD5: ??? (in /bin/dash)
          n1: 96 0x40A88C: ??? (in /bin/dash)
           n1: 96 0x402159: ??? (in /bin/dash)
            n0: 96 0x4E4E76B: (below main) (libc-start.c:226)
       n1: 32 0x41212F: ??? (in /bin/dash)
        n1: 32 0x4020E4: ??? (in /bin/dash)
         n0: 32 0x4E4E76B: (below main) (libc-start.c:226)