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big tables slow down due to tmp table actions, please help review .ini

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  • big tables slow down due to tmp table actions, please help review .ini

    Hello,

    we have a windows 2003 box with mySQL 5.0 and a database with some huge tables (about 4,5 milion records each). When some php scripts are querying these tables it takes a lot of time creating a sorting index and then the system goes on writing tmp tables for about a minute, and locking all the other queries.

    We have 2.8GHz Xeon with 2GB Ram... i am wondering if something is screwed up with my mysql.ini configuration, so maybe someone might be so helpfull to check it and see if something is configured completely stupid?

    cheers in advance! Olaf


    # MySQL Server Instance Configuration File# ----------------------------------------------------------------------# Generated by the MySQL Server Instance Configuration Wizard### Installation Instructions# ----------------------------------------------------------------------## On Linux you can copy this file to /etc/my.cnf to set global options,# mysql-data-dir/my.cnf to set server-specific options# (@localstatedir@ for this installation) or to# ~/.my.cnf to set user-specific options.## On Windows you should keep this file in the installation directory # of your server (e.g. C:\Program Files\MySQL\MySQL Server 4.1). To# make sure the server reads the config file use the startup option # "--defaults-file". ## To run run the server from the command line, execute this in a # command line shell, e.g.# mysqld --defaults-file="C:\Program Files\MySQL\MySQL Server 4.1\my.ini"## To install the server as a Windows service manually, execute this in a # command line shell, e.g.# mysqld --install MySQL41 --defaults-file="C:\Program Files\MySQL\MySQL Server 4.1\my.ini"## And then execute this in a command line shell to start the server, e.g.# net start MySQL41### Guildlines for editing this file# ----------------------------------------------------------------------## In this file, you can use all long options that the program supports.# If you want to know the options a program supports, start the program# with the "--help" option.## More detailed information about the individual options can also be# found in the manual.### CLIENT SECTION# ----------------------------------------------------------------------## The following options will be read by MySQL client applications.# Note that only client applications shipped by MySQL are guaranteed# to read this section. If you want your own MySQL client program to# honor these values, you need to specify it as an option during the# MySQL client library initialization.#[client]port=3306[mysql]default-character-set=latin1# SERVER SECTION# ----------------------------------------------------------------------## The following options will be read by the MySQL Server. Make sure that# you have installed the server correctly (see above) so it reads this # file.#[mysqld]# The TCP/IP Port the MySQL Server will listen onport=3306#Path to installation directory. All paths are usually resolved relative to this.basedir="C:/Program Files/MySQL/MySQL Server 5.0/"#Path to the database rootdatadir="C:/Program Files/MySQL/MySQL Server 5.0/Data/"# The default character set that will be used when a new schema or table is# created and no character set is defineddefault-character-set=latin1# The default storage engine that will be used when create new tables whendefault-storage-engine=innodb# The maximum amount of concurrent sessions the MySQL server will# allow. One of these connections will be reserved for a user with# SUPER privileges to allow the administrator to login even if the# connection limit has been reached.max_connections=250# Query cache is used to cache SELECT results and later return them# without actual executing the same query once again. Having the query# cache enabled may result in significant speed improvements, if your# have a lot of identical queries and rarely changing tables. See the# "Qcache_lowmem_prunes" status variable to check if the current value# is high enough for your load.# Note: In case your tables change very often or if your queries are# textually different every time, the query cache may result in a# slowdown instead of a performance improvement.query_cache_size=100# The number of open tables for all threads. Increasing this value# increases the number of file descriptors that mysqld requires.# Therefore you have to make sure to set the amount of open files# allowed to at least 4096 in the variable "open-files-limit" in# section [mysqld_safe]table_cache=256# Maximum size for internal (in-memory) temporary tables. If a table# grows larger than this value, it is automatically converted to disk# based table This limitation is for a single table. There can be many# of them.tmp_table_size=250M# How many threads we should keep in a cache for reuse. When a client# disconnects, the client's threads are put in the cache if there aren't# more than thread_cache_size threads from before. This greatly reduces# the amount of thread creations needed if you have a lot of new# connections. (Normally this doesn't give a notable performance# improvement if you have a good thread implementation.)thread_cache_size=8#*** MyISAM Specific options# The maximum size of the temporary file MySQL is allowed to use while# recreating the index (during REPAIR, ALTER TABLE or LOAD DATA INFILE.# If the file-size would be bigger than this, the index will be created# through the key cache (which is slower).myisam_max_sort_file_size=100G# If the temporary file used for fast index creation would be bigger# than using the key cache by the amount specified here, then prefer the# key cache method. This is mainly used to force long character keys in# large tables to use the slower key cache method to create the index.myisam_max_extra_sort_file_size=100G# If the temporary file used for fast index creation would be bigger# than using the key cache by the amount specified here, then prefer the# key cache method. This is mainly used to force long character keys in# large tables to use the slower key cache method to create the index.myisam_sort_buffer_size=205M# Size of the Key Buffer, used to cache index blocks for MyISAM tables.# Do not set it larger than 30% of your available memory, as some memory# is also required by the OS to cache rows. Even if you're not using# MyISAM tables, you should still set it to 8-64M as it will also be# used for internal temporary disk tables.key_buffer_size=375M# Size of the buffer used for doing full table scans of MyISAM tables.# Allocated per thread, if a full scan is needed.read_buffer_size=64Kread_rnd_buffer_size=25 6K# This buffer is allocated when MySQL needs to rebuild the index in# REPAIR, OPTIMZE, ALTER table statements as well as in LOAD DATA INFILE# into an empty table. It is allocated per thread so be careful with# large settings.sort_buffer_size=256K#*** INNODB Specific options ***# Use this option if you have a MySQL server with InnoDB support enabled# but you do not plan to use it. This will save memory and disk space# and speed up some things.#skip-innodb# Additional memory pool that is used by InnoDB to store metadata# information. If InnoDB requires more memory for this purpose it will# start to allocate it from the OS. As this is fast enough on most# recent operating systems, you normally do not need to change this# value. SHOW INNODB STATUS will display the current amount used.innodb_additional_mem_pool_size=7M# If set to 1, InnoDB will flush (fsync) the transaction logs to the# disk at each commit, which offers full ACID behavior. If you are# willing to compromise this safety, and you are running small# transactions, you may set this to 0 or 2 to reduce disk I/O to the# logs. Value 0 means that the log is only written to the log file and# the log file flushed to disk approximately once per second. Value 2# means the log is written to the log file at each commit, but the log# file is only flushed to disk approximately once per second.innodb_flush_log_at_trx_commit=1# The size of the buffer InnoDB uses for buffering log data. As soon as# it is full, InnoDB will have to flush it to disk. As it is flushed# once per second anyway, it does not make sense to have it very large# (even with long transactions).innodb_log_buffer_size=3498K# InnoDB, unlike MyISAM, uses a buffer pool to cache both indexes and# row data. The bigger you set this the less disk I/O is needed to# access data in tables. On a dedicated database server you may set this# parameter up to 80% of the machine physical memory size. Do not set it# too large, though, because competition of the physical memory may# cause paging in the operating system. Note that on 32bit systems you# might be limited to 2-3.5G of user level memory per process, so do not# set it too high.innodb_buffer_pool_size=339M# Size of each log file in a log group. You should set the combined size# of log files to about 25%-100% of your buffer pool size to avoid# unneeded buffer pool flush activity on log file overwrite. However,# note that a larger logfile size will increase the time needed for the# recovery process.innodb_log_file_size=170M# Number of threads allowed inside the InnoDB kernel. The optimal value# depends highly on the application, hardware as well as the OS# scheduler properties. A too high value may lead to thread thrashing.innodb_thread_concurrency=2#Use old password encryption method (needed for 4.0 and older clients).old-passwordsset-variable = delay_key_write=allset-variable = max_allowed_packet=2Mset-variable = sort_buffer=2Mset-variable = record_buffer=2Mset-variable = myisam_sort_buffer_size=512Mset-variable = query_cache_limit=2Mset-variable = query_cache_size=16Mset-variable = thread_cache=128# Try number of CPU's*2 for thread_concurrencyset-variable = thread_concurrency=2set-variable = max_connections=256set-variable = max_connect_errors=1000

  • #2
    anyone? )

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    • #3
      Another question - do you have index on the needed rows? Could be that index will make your queries faster without changing my.ini...

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      • #4
        yes the needed indexes are available.
        I've been testing some more, and it seems that our biggest problem are huge tables that are to big to fit into mySQL assigned memory, and are thus written as tmp tables to the filesystem.
        I've increased the tmp table memory pool quiet a bit and it increases the performance somewhat, until the tables get to big to fit into our available physical memory.

        I guess we have to add some more RAM or start requesting data-partitioning.

        Olaf

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        • #5
          olafmol wrote on Tue, 08 January 2008 10:53

          yes the needed indexes are available.
          I've been testing some more, and it seems that our biggest problem are huge tables that are to big to fit into mySQL assigned memory, and are thus written as tmp tables to the filesystem.
          I've increased the tmp table memory pool quiet a bit and it increases the performance somewhat, until the tables get to big to fit into our available physical memory.

          I guess we have to add some more RAM or start requesting data-partitioning.

          Olaf


          Ok, so my idea was not so good. How to set up the my.ini in best way is also my problem (out of memory error messages) (

          Comment


          • #6
            Some questions:
            1.
            Are you using both InnoDB and MyISAM tables?
            Because right now you are assigning:
            key_buffer_size=375M (only used by MyISAM)
            innodb_buffer_pool_size=339M (only used by InnoDB)
            and if you only have 2GB in that server then the combination of these two on top of the other very high settings that you have can very well get the server to start swapping.

            2.
            Your sort buffer settings are a bit strange:
            First of all you are actually setting it twice in the ini file:
            sort_buffer_size=256K
            set-variable = sort_buffer=2M

            But it is also _very_ small.
            This forces any query with a result set larger than 2MB and contains a ORDER BY or GROUP BY that can't use an index to be written to a temporary table on disk.

            My recommendation is that you should increase this value and reduce some of the extremely large values that you have in your setup.

            You should also check the total amount of used memory on your server during these peek times. Because if the OS starts to swap you will get a drastic reduction of performance. It's always better to keep a pretty big headroom up to max memory usage than to allow the server to take so much that the OS starts to swap. Because you loose so much more when the OS starts to swap than giving the last MB's of RAM to MySQL can gain.

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