1. I am experiencing a problem where the server runs out of memory in specific scenarios. one solution I am thinking about is to limit the number of clients served concurrently, but have the extra clients wait for a free slot instead of having them get a "too many connections error". is this possible?

  2. how do I calculate maximum memory usage per open mysql connection?

2 Answers 2


take a look in my.cnf (should be somewhere in /etc or /etc/mysql, depending on your distro); there you have several options for fine tuning, like

  • max_connections
  • max_connect_errors
  • max_delayed_threads
  • max_user_connections

and some query cache options

  • this does not really answer my question. limiting max_connections results in an error if the number of connections is reached (instead of the desired 'wait for a free slot' behavior).
    – Omry
    Aug 30, 2009 at 14:53
  • I don't think you can setup a waiting queue; all connections coming after the "slots" have been filled up are discarded
    – quaie
    Aug 30, 2009 at 16:34

How much memory is the database using? How much is installed? What OS are you running MySQL on?

  • Debian lenny, and the machine has 4GB of RAM and is also doing other things. lets assume mysql cannot handle the peak usage (with the required max_allowed_packet - there are big inserts). is there a way to achieve what I specified by tweaking mysql?
    – Omry
    Aug 30, 2009 at 14:56
  • key_buffer = 512M max_allowed_packet = 64M thread_stack = 128K thread_cache_size = 32K max_connections = 350 table_cache = 256 thread_concurrency = 8 sort_buffer_size = 64M wait_timeout = 20 query_cache_limit = 64M query_cache_size = 512M query_alloc_block_size = 4M query_prealloc_size = 128M [mysqldump] quick quote-names max_allowed_packet = 16M [mysql] [isamchk] key_buffer = 16M ########## try those or modify the left values to your needs
    – quaie
    Aug 30, 2009 at 22:12
  • If changing those settings doesn't correct the issue, you may need to increase the amount of RAM in the server. 4 Gigs for a busy server isn't a whole lot.
    – mrdenny
    Aug 31, 2009 at 2:40

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