To change the value of the AUTO_INCREMENT counter to be used for new rows: ALTER TABLE mytable AUTO_INCREMENT = value (Storing 0 is not a recommended practice, by the way.) This mode can be useful if 0 has been stored in a table's AUTO_INCREMENT column. NO_AUTO_VALUE_ON_ZERO suppresses auto increment for 0 so that only NULL generates the next sequence number. Use the IS NULL and IS NOT NULL operators instead: To test for NULL, you cannot use the arithmetic comparison operators such as =. Usually, you create all the indexes you need when you are creating tables.Īny column declared as PRIMARY KEY, KEY, UNIQUE, or INDEX will be indexed. In MySQL, the name of a PRIMARY KEY is PRIMARYĬurrently, only InnoDB (v5.1?) tables support foreign keys. You can also refer to the column as "_rowid" in SELECT statements. If a PRIMARY KEY or UNIQUE index consists of only one column that has an integer type, This was implemented for compatibility with other database systems.Ī PRIMARY KEY is a unique index where all key columns must be defined as NOT NULL The key attribute PRIMARY KEY can also be specified as just KEY when given in a column definition. There can be only one AUTO_INCREMENT column per table, it must be indexed, and it cannot have a DEFAULT value Increase the value until your threads_created do not grow very quickly. a web site without persistent connections) you might improve performance by setting thread_cache_size to a non-zero value. If you have many connects established (i.e. Note: be careful not to run out of memory. For example sort_buffer_size is allocated only if MySQL needs to do a sort. So, consider your load and available resource when setting these parameters. Note: These are "per connection" values, among read_buffer_size, read_rnd_buffer_size and some others, meaning that this value might be needed for each connection. Values will depend on the query complexity and available resources, but 4Mb and 32Mb, respectively are recommended starting points. If you have complex queries sort_buffer_size and tmp_table_size are likely to be very important. MySQL on Linux has an open_file_limit option, set this limit. 20+max_connections+table_cache*2 is a good estimate for what you need. The 2 previous parameters may require a lot of open files. Watch the open_tables value and if it is growing quickly you will need to increase its size. Set table_cache to match the number of your open tables and concurrent connections. MySQL binaries for Linux/x86 allow you to have up to 4096 concurrent connections, but self compiled binaries often have less of a limit. The default value is 100 connections (151 since 5.0) - very small.Ĭonnections take memory and your OS might not be able to handle a lot of connections. Max_connections is the number of concurrent connections. While the simple queries required for most B2C applications may work well for MySQL, most of the aggregate reporting type of queries needed for Intelligence Reporting seems to require a fair bit of planning and re-organizing the SQL queries to guide MySQL to execute them faster. And my reading on MySQL tuning makes me conclude that MySQL is behind Oracle in terms of optimizing queries. Having come from Oracle database world, things I took for granted weren’t working the same with MySQL. In general, all the SQLs I tuned today required using sub-queries. Since you put up a bounty, I'll share my hard won secrets.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |