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5.2.2. Server System Variables

The mysql server maintains many system variables that indicate how it is configured. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically while the server is running by means of the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can refer to system variable values in expressions.

There are several ways to see the names and values of system variables:

  • To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:

    mysqld --verbose --help
    
  • To see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command:

    mysqld --no-defaults --verbose --help
    
  • To see the current values used by a running server, use the SHOW VARIABLES statement.

This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.1 releases. For historical information concerning their implementation, please see MySQL 5.0 Reference Manual and MySQL 3.23, 4.0, 4.1 Reference Manual.

For additional system variable information, see these sections:

Note: Some of the following variable descriptions refer to “enabling” or “disabling” a variable. These variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. However, to set such a variable on the command line or in an option file, you must set it to 1 or 0; setting it to ON or OFF will not work. For example, on the command line, --delay_key_write=1 works but --delay_key_write=ON does not.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

  • auto_increment_increment

    auto_increment_increment and auto_increment_offset are intended for use with master-to-master replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables can be set globally or locally, and each can assume an integer value between 1 and 65,535 inclusive. Setting the value of either of these two variables to 0 causes its value to be set to 1 instead. Attempting to set the value of either of these two variables to an integer greater than 65,535 or less than 0 causes its value to be set to 65,535 instead. Attempting to set the value of auto_increment_increment or auto_increment_offset to a non-integer value gives rise to an error, and the actual value of the variable remains unchanged.

    These two variables effect AUTO_INCREMENT column behavior as follows:

    • auto_increment_increment controls the interval between successive column values. For example:

      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 1     |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc1
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
        Query OK, 0 rows affected (0.04 sec)
      
      mysql> SET @@auto_increment_increment=10;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.01 sec)
      
      mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc1;
      +-----+
      | col |
      +-----+
      |   1 |
      |  11 |
      |  21 |
      |  31 |
      +-----+
      4 rows in set (0.00 sec)
      

      (Note how SHOW VARIABLES is used here to obtain the current values for these variables.)

    • auto_increment_offset determines the starting point for the AUTO_INCREMENT column value. Consider the following, assuming that these statements are executed during the same session as the example given in the description for auto_increment_increment:

      mysql> SET @@auto_increment_offset=5;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 5     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc2
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
      Query OK, 0 rows affected (0.06 sec)
      
      mysql> INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc2;
      +-----+
      | col |
      +-----+
      |   5 |
      |  15 |
      |  25 |
      |  35 |
      +-----+
      4 rows in set (0.02 sec)
      

      If the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored.

    Should one or both of these variables be changed and then new rows inserted into a table containing an AUTO_INCREMENT column, the results may seem counterintuitive because the series of AUTO_INCREMENT values is calculated without regard to any values already present in the column, and the next value inserted is the least value in the series that is greater than the maximum existing value in the AUTO_INCREMENT column. In other words, the series is calculated like so:

    auto_increment_offset + N × auto_increment_increment

    where N is a positive integer value in the series [1, 2, 3, ...]. For example:

    mysql> SHOW VARIABLES LIKE 'auto_inc%';
    +--------------------------+-------+
    | Variable_name            | Value |
    +--------------------------+-------+
    | auto_increment_increment | 10    |
    | auto_increment_offset    | 5     |
    +--------------------------+-------+
    2 rows in set (0.00 sec)
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    +-----+
    4 rows in set (0.00 sec)
    
    mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
    Query OK, 4 rows affected (0.00 sec)
    Records: 4  Duplicates: 0  Warnings: 0
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    |  35 |
    |  45 |
    |  55 |
    |  65 |
    +-----+
    8 rows in set (0.00 sec)
    

    The values shown for auto_increment_increment and auto_increment_offset generate the series 5 + N × 10, that is, [5, 15, 25, 35, 45, ...]. The greatest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query.

    It is important to remember that it is not possible to confine the effects of these two variables to a single table, and thus they do not take the place of the sequences offered by some other database management systems; these variables control the behavior of all AUTO_INCREMENT columns in all tables on the MySQL server. If one of these variables is set globally, its effects persist until the global value is changed or overridden by setting them locally, or until mysqld is restarted. If set locally, the new value affects AUTO_INCREMENT columns for all tables into which new rows are inserted by the current user for the duration of the session, unless the values are changed during that session.

    The default value of auto_increment_increment is 1. See Section 6.15, “Auto-Increment in Multiple-Master Replication”.

  • auto_increment_offset

    This variable has a default value of 1. For particulars, see the description for auto_increment_increment.

  • back_log

    The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

    In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. back_log cannot be set higher than your operating system limit.

  • basedir

    The MySQL installation base directory. This variable can be set with the --basedir option.

  • bdb_cache_parts

    The number of parts to use for the BDB cache. Added in MySQL 5.1.2.

  • bdb_cache_size

    The size of the buffer that is allocated for caching indexes and rows for BDB tables. Some systems support setting this variable larger than 4GB. If you don't use BDB tables, you should start mysqld with --skip-bdb to not allocate memory for this cache.

  • bdb_home

    The base directory for BDB tables. This should be assigned the same value as the datadir variable.

  • bdb_log_buffer_size

    The size of the buffer that is allocated for caching indexes and rows for BDB tables. If you don't use BDB tables, you should set this to 0 or start mysqld with --skip-bdb to not allocate memory for this cache.

  • bdb_logdir

    The directory where the BDB storage engine writes its log files. This variable can be set with the --bdb-logdir option.

  • bdb_max_lock

    The maximum number of locks that can be active for a BDB table (10,000 by default). You should increase this value if errors such as the following occur when you perform long transactions or when mysqld has to examine many rows to calculate a query:

    bdb: Lock table is out of available locks
    Got error 12 from ...
    
  • bdb_region_size

    The size of the underlying logging area of the BDB environment. This is the size of the memory pool used for storing the filenames used in a transaction. Added in MySQL 5.1.2.

  • bdb_shared_data

    This is ON if you are using --bdb-shared-data to start Berkeley DB in multi-process mode. (Do not use DB_PRIVATE when initializing Berkeley DB.)

  • bdb_tmpdir

    The BDB temporary file directory.

  • binlog_cache_size

    The size of the cache to hold the SQL statements for the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large, multiple-statement transactions, you can increase this cache size to get more performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 5.11.4, “The Binary Log”.

  • binlog_format

    The binary logging format, either STATEMENT or ROW. binlog_format is set by the --binlog-format option. See Section 6.3, “Row-Based Replication”. This variable was added in MySQL 5.1.5.

  • bulk_insert_buffer_size

    MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA INFILE when adding data to non-empty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

  • character_set_client

    The character set for statements that arrive from the client.

  • character_set_connection

    The character set used for literals that do not have a character set introducer and for number-to-string conversion.

  • character_set_database

    The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

  • character_set_filesystem

    The filesystem character set. This variable is used to interpret string literals that refer to filenames, such as in the LOAD DATA INFILE and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such filenames are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multi-byte filenames are allowed, a different value may be more appropriate. For example, if the system represents filenames using UTF-8, set character_set_filesytem to 'utf8'. This variable was added in MySQL 5.1.6.

  • character_set_results

    The character set used for returning query results to the client.

  • character_set_server

    The server's default character set.

  • character_set_system

    The character set used by the server for storing identifiers. The value is always utf8.

  • character_sets_dir

    The directory where character sets are installed.

  • collation_connection

    The collation of the connection character set.

  • collation_database

    The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

  • collation_server

    The server's default collation.

  • completion_type

    The transaction completion type:

    • If the value is 0 (the default), COMMIT and ROLLBACK are unaffected.

    • If the value is 1, COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)

    • If the value is 2, COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

  • concurrent_insert

    If ON (the default), MySQL allows INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle. You can turn this option off by starting mysqld with --safe or --skip-new.

    This variable can take three integer values:

    Value Description
    0 Off
    1 (Default) Enables concurrent insert for MyISAM tables that don't have holes
    2 Enables concurrent inserts for all MyISAM tables. If table has a hole and is in use by another thread the new row will be inserted at end of table. If table is not in use then MySQL does a normal read lock and inserts the new row into the hole.

    See also Section 7.3.3, “Concurrent Inserts”.

  • connect_timeout

    The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake.

  • datadir

    The MySQL data directory. This variable can be set with the --datadir option.

  • date_format

    This variable is not implemented.

  • datetime_format

    This variable is not implemented.

  • default_week_format

    The default mode value to use for the WEEK() function. See Section 12.5, “Date and Time Functions”.

  • delay_key_write

    This option applies only to MyISAM tables. It can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used in CREATE TABLE statements.

    Option Description
    OFF DELAY_KEY_WRITE is ignored.
    ON MySQL honors any DELAY_KEY_WRITE option specified in CREATE TABLE statements. This is the default value.
    ALL All new opened tables are treated as if they were created with the DELAY_KEY_WRITE option enabled.

    If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the --myisam-recover option (for example, --myisam-recover=BACKUP,FORCE). See Section 5.2.1, “mysqld Command Options”, and Section 14.1.1, “MyISAM Startup Options”.

    Note that enabling external locking with --external-locking offers no protection against index corruption for tables that use delayed key writes.

  • delayed_insert_limit

    After inserting delayed_insert_limit delayed rows, the INSERT DELAYED handler thread checks whether there are any SELECT statements pending. If so, it allows them to execute before continuing to insert delayed rows.

  • delayed_insert_timeout

    How many seconds an INSERT DELAYED handler thread should wait for INSERT statements before terminating.

  • delayed_queue_size

    This is a per-table limit on the number of rows to queue when handling INSERT DELAYED statements. If the queue becomes full, any client that issues an INSERT DELAYED statement waits until there is room in the queue again.

  • div_precision_increment

    This variable indicates the number of digits of precision by which to increase the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.

    mysql> SELECT 1/7;
    +--------+
    | 1/7    |
    +--------+
    | 0.1429 |
    +--------+
    mysql> SET div_precision_increment = 12;
    mysql> SELECT 1/7;
    +----------------+
    | 1/7            |
    +----------------+
    | 0.142857142857 |
    +----------------+
    
  • event_scheduler

    Whether the event scheduler is disabled or enabled. By default, the scheduler is disabled. This variable was added in MySQL 5.1.6.

  • engine_condition_pushdown

    This variable applies to NDB. By default it is 0 (OFF): If you execute a query such as SELECT * FROM t WHERE mycol = 42, where mycol is a non-indexed column, the query is executed as a full table scan on every NDB node. Each node sends every row to the MySQL server, which applies the WHERE condition. If engine_condition_pushdown is set to 1 (ON), the condition is “pushed down” to the storage engine and sent to the NDB nodes. Each node uses the condition to perform the scan, and only sends back to the MySQL server the rows that match the condition.

  • expire_logs_days

    The number of days for automatic binary log removal. The default is 0, which means “no automatic removal.” Possible removals happen at startup and at binary log rotation.

  • flush

    If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section A.4.2, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

  • flush_time

    If this is set to a non-zero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. We recommend that this option be used only on Windows 9x or Me, or on systems with minimal resources.

  • ft_boolean_syntax

    The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 12.7.1, “Boolean Full-Text Searches”.

    The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

    • Operator function is determined by position within the string.

    • The replacement value must be 14 characters.

    • Each character must be an ASCII non-alphanumeric character.

    • Either the first or second character must be a space.

    • No duplicates are allowed except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.

    • Positions 10, 13, and 14 (which by default are set to ‘:’, ‘&’, and ‘|’) are reserved for future extensions.

  • ft_max_word_len

    The maximum length of the word to be included in a FULLTEXT index.

    Note: FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_min_word_len

    The minimum length of the word to be included in a FULLTEXT index.

    Note: FULLTEXT indexes must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

  • ft_query_expansion_limit

    The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.

  • ft_stopword_file

    The file from which to read the list of stopwords for full-text searches. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering.

    Note: FULLTEXT indexes must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

  • group_concat_max_len

    The maximum allowed result length for the GROUP_CONCAT() function. The default is 1024.

  • have_archive

    YES if mysqld supports ARCHIVE tables, NO if not.

  • have_bdb

    YES if mysqld supports BDB tables. DISABLED if --skip-bdb is used.

  • have_blackhole_engine

    YES if mysqld supports BLACKHOLE tables, NO if not.

  • have_compress

    YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.

  • have_crypt

    YES if the crypt() system call is available to the server, NO if not. If not, the ENCRYPT() function cannot be used.

  • have_csv

    YES if mysqld supports ARCHIVE tables, NO if not.

  • have_example_engine

    YES if mysqld supports EXAMPLE tables, NO if not.

    have_federated_engine

    YES if mysqld supports FEDERATED tables, NO if not.

  • have_geometry

    YES if the server supports spatial data types, NO if not.

  • have_innodb

    YES if mysqld supports InnoDB tables. DISABLED if --skip-innodb is used.

  • have_ndbcluster

    YES if mysqld supports NDB Cluster tables. DISABLED if --skip-ndbcluster is used.

  • have_partitioning

    YES if mysqld supports partitioning. Added in MySQL 5.1.1 as have_partition_engine and renamed to have_partioning in 5.1.6.

  • have_openssl

    YES if mysqld supports SSL (encryption) of the client/server protocol, NO if not.

  • have_query_cache

    YES if mysqld supports the query cache, NO if not.

  • have_row_based_replication

    YES if the server can perform replication using row-based binary logging. If the value is NO, the server can use only statement-based logging. See Section 6.3, “Row-Based Replication”. This variable was added in MySQL 5.1.5.

  • have_rtree_keys

    YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)

  • have_symlink

    YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options, and on Windows for support of data directory symlinks.

  • init_connect

    A string to be executed by the server for each client that connects. The string consists of one or more SQL statements. To specify multiple statements, separate them by semicolon characters. For example, each client begins by default with autocommit mode enabled. There is no global system variable to specify that autocommit should be disabled by default, but init_connect can be used to achieve the same effect:

    SET GLOBAL init_connect='SET AUTOCOMMIT=0';
    

    This variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:

    [mysqld]
    init_connect='SET AUTOCOMMIT=0'
    

    Note that the content of init_connect is not executed for users that have the SUPER privilege. This is done so that an erroneous value for init_connect does not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executing init_connect for users that have the SUPER privilege enables them to open a connection and fix the init_connect value.

  • init_file

    The name of the file specified with the --init-file option when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments.

  • init_slave

    This variable is similar to init_connect, but is a string to be executed by a slave server each time the SQL thread starts. The format of the string is the same as for the init_connect variable.

  • innodb_xxx

    InnoDB system variables are listed in Section 14.2.4, “InnoDB Startup Options and System Variables”.

  • interactive_timeout

    The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

  • join_buffer_size

    The size of the buffer that is used for joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

  • key_buffer_size

    Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

    The maximum allowable setting for key_buffer_size is 4GB. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform.

    Increase the value to get better index handling (for all reads and multiple writes) to as much as you can afford. Using a value that is 25% of total memory on a machine that mainly runs MySQL is quite common. However, if you make the value too large (for example, more than 50% of your total memory) your system might start to page and become extremely slow. MySQL relies on the operating system to perform filesystem caching for data reads, so you must leave some room for the filesystem cache. Consider also the memory requirements of other storage engines.

    For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 7.2.16, “Speed of INSERT Statements”.

    You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 13.5.4, “SHOW Syntax”.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

    The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

    1 - ((Key_blocks_unused × key_cache_block_size) / key_buffer_size)
    

    This value is an approximation because some space in the key buffer may be allocated internally for administrative structures.

    It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_age_threshold

    This value controls the demotion of buffers from the hot sub-chain of a key cache to the warm sub-chain. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_block_size

    The size in bytes of blocks in the key cache. The default value is 1024. See Section 7.4.6, “The MyISAM Key Cache”.

  • key_cache_division_limit

    The division point between the hot and warm sub-chains of the key cache buffer chain. The value is the percentage of the buffer chain to use for the warm sub-chain. Allowable values range from 1 to 100. The default value is 100. See Section 7.4.6, “The MyISAM Key Cache”.

  • language

    The language used for error messages.

  • large_file_support

    Whether mysqld was compiled with options for large file support.

  • large_pages

    Whether large page support is enabled.

  • license

    The type of license the server has.

  • local_infile

    Whether LOCAL is supported for LOAD DATA INFILE statements. See Section 5.6.4, “Security Issues with LOAD DATA LOCAL.

  • locked_in_memory

    Whether mysqld was locked in memory with --memlock.

  • log

    Whether logging of all statements to the general query log is enabled. See Section 5.11.3, “The General Query Log”.

  • log_bin

    Whether the binary log is enabled. See Section 5.11.4, “The Binary Log”.

  • log_bin_trust_function_creators

    This variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not allowed to create or alter stored routines unless they have the SUPER privilege in addition to the CREATE ROUTINE or ALTER ROUTINE privilege. A setting of 0 also enforces the restriction that a function must be declared with the DETERMINISTIC characteristic, or with the READS SQL DATA or NO SQL characteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. See Section 19.4, “Binary Logging of Stored Routines and Triggers”.

  • log_error

    The location of the error log.

  • log_slave_updates

    Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this to have any effect. See Section 6.9, “Replication Startup Options”.

  • log_slow_queries

    Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. See Section 5.11.5, “The Slow Query Log”.

  • log_warnings

    Whether to produce additional warning messages. It is enabled (1) by default. Aborted connections are not logged to the error log unless the value is greater than 1.

  • long_query_time

    If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If you are using the --log-slow-queries option, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum value is 1. See Section 5.11.5, “The Slow Query Log”.

  • low_priority_updates

    If set to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. This variable previously was named sql_low_priority_updates.

  • lower_case_file_system

    This variable describes the case sensitivity of filenames on the filesystem where the data directory is located. OFF means filenames are case sensitive, ON means they are not case sensitive.

  • lower_case_table_names

    If set to 1, table names are stored in lowercase on disk and table name comparisons are not case sensitive. If set to 2 table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. See Section 9.2.2, “Identifier Case Sensitivity”.

    If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

    You should not set this variable to 0 if you are running MySQL on a system that does not have case-sensitive filenames (such as Windows or Mac OS X). If this variable is not set at startup and the filesystem on which the data directory is located does not have case-sensitive filenames, MySQL automatically sets lower_case_table_names to 2.

  • max_allowed_packet

    The maximum size of one packet or any generated/intermediate string.

    The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch large (possibly incorrect) packets.

    You must increase this value if you are using large BLOB columns or long strings. It should be as big as the biggest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB.

  • max_binlog_cache_size

    If a multiple-statement transaction requires more than this amount of memory, the server generates a Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage error.

  • max_binlog_size

    If a write to the binary log causes the current log file size to exceed the value of this variable, the server rotates the binary logs (closes the current file and opens the next one). You cannot set this variable to more than 1GB or to less than 4096 bytes. The default value is 1GB.

    A transaction is written in one chunk to the binary log, so it is never split between several binary logs. Therefore, if you have big transactions, you might see binary logs larger than max_binlog_size.

    If max_relay_log_size is 0, the value of max_binlog_size applies to relay logs as well.

  • max_connect_errors

    If there are more than this number of interrupted connections from a host, that host is blocked from further connections. You can unblock blocked hosts with the FLUSH HOSTS statement.

  • max_connections

    The number of simultaneous client connections allowed. Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.8, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits. See also Section A.2.6, “Too many connections.

  • max_delayed_threads

    Do not start more than this number of threads to handle INSERT DELAYED statements. If you try to insert data into a new table after all INSERT DELAYED threads are in use, the row is inserted as if the DELAYED attribute wasn't specified. If you set this to 0, MySQL never creates a thread to handle DELAYED rows; in effect, this disables DELAYED entirely.

  • max_error_count

    The maximum number of error, warning, and note messages to be stored for display by the SHOW ERRORS and SHOW WARNINGS statements.

  • max_heap_table_size

    This variable sets the maximum size to which MEMORY tables are allowed to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values. Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or altered with ALTER TABLE or TRUNCATE TABLE.

  • max_insert_delayed_threads

    This variable is a synonym for max_delayed_threads.

  • max_join_size

    Do not allow SELECT statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_join_size disk seeks. By setting this value, you can catch SELECT statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack a WHERE clause, that take a long time, or that return millions of rows.

    Setting this variable to a value other than DEFAULT resets the value of SQL_BIG_SELECTS to 0. If you set the SQL_BIG_SELECTS value again, the max_join_size variable is ignored.

    If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.

    This variable previously was named sql_max_join_size.

  • max_length_for_sort_data

    The cutoff on the size of index values that determines which filesort algorithm to use. See Section 7.2.12, “ORDER BY Optimization”.

  • max_relay_log_size

    If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 6.4, “Replication Implementation Details”.

  • max_seeks_for_key

    Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 13.5.4.15, “SHOW INDEX Syntax”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.

  • max_sort_length

    The number of bytes to use when sorting BLOB or TEXT values. Only the first max_sort_length bytes of each value are used; the rest are ignored.

  • max_tmp_tables

    The maximum number of temporary tables a client can keep open at the same time. (This option does not yet do anything.)

  • max_user_connections

    The maximum number of simultaneous connections allowed to any given MySQL account. A value of 0 means “no limit.

    This variable has both a global scope and a (read-only) session scope. The session variable has the same value as the global variable unless the current account has a non-zero MAX_USER_CONNECTIONS resource limit. In that case, the session value reflects the account limit.

  • max_write_lock_count

    After this many write locks, allow some pending read lock requests to be processed in between.

  • myisam_data_pointer_size

    The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section A.2.11, “The table is full.

  • myisam_max_extra_sort_file_size (DEPRECATED)

    Note: This variable is not supported in MySQL 5.1. See MySQL 5.0 Reference Manual for more information.

  • myisam_max_sort_file_size

    The maximum size of the temporary file MySQL is allowed to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA INFILE). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.

  • myisam_recover_options

    The value of the --myisam-recover option. See Section 5.2.1, “mysqld Command Options”.

  • myisam_repair_threads

    If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1. Note: Multi-threaded repair is still beta-quality code.

  • myisam_sort_buffer_size

    The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

  • myisam_stats_method

    How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has two possible values, nulls_equal and nulls_unequal. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1.

    The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 7.4.7, “MyISAM Index Statistics Collection”.

  • myisam_use_mmap

    Use memory mapping for reading and writing MyISAM tables. This variable was added in MySQL 5.1.4.

  • multi_read_range

    Specifies the maximum number of ranges to send to a storage engine during range selects. The default value is 256. Sending multiple ranges to an engine is a feature that can improve the performance of certain selects dramatically, particularly for NDBCLUSTER. This engine needs to send the range requests to all nodes, and sending many of those requests at once reduces the communication costs significantly.

  • named_pipe

    (Windows only.) Indicates whether the server supports connections over named pipes.

  • ndb_extra_logging

    This variable can be set to a non-zero value to enable extra NDB logging. This variable was added in MySQL 5.1.6.

  • net_buffer_length

    The communication buffer is reset to this size between SQL statements. This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to max_allowed_packet bytes.

  • net_read_timeout

    The number of seconds to wait for more data from a connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.

  • net_retry_count

    If a read on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.

  • net_write_timeout

    The number of seconds to wait for a block to be written to a connection before aborting the write. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory. See also net_read_timeout.

  • new

    This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. In MySQL 5.1, its value is always OFF.

  • old_passwords

    Whether the server should use pre-4.1-style passwords for MySQL user accounts. See Section A.2.3, “Client does not support authentication protocol.

  • one_shot

    This is not a variable, but it can be used when setting some variables. It is described in Section 13.5.3, “SET Syntax”.

  • open_files_limit

    The number of files that the operating system allows mysqld to open. This is the real value allowed by the system and might be different from the value you gave using the --open-files-limit option to mysqld or mysqld_safe. The value is 0 on systems where MySQL can't change the number of open files.

  • optimizer_prune_level

    Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.

  • optimizer_search_depth

    The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value. If set to the maximum number of tables used in a query plus 2, the optimizer switches to the algorithm used in MySQL 5.0.0 (and previous versions) for performing searches.

  • pid_file

    The pathname of the process ID (PID) file. This variable can be set with the --pid-file option.

  • plugin_dir

    The pathname of the plugins directory. This variable was added in MySQL 5.1.2.

  • port

    The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.

  • preload_buffer_size

    The size of the buffer that is allocated when preloading indexes.

  • protocol_version

    The version of the client/server protocol used by the MySQL server.

  • query_alloc_block_size

    The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this a bit.

  • query_cache_limit

    Don't cache results that are larger than this number of bytes. The default value is 1MB.

  • query_cache_min_res_unit

    The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 5.13.3, “Query Cache Configuration”.

  • query_cache_size

    The amount of memory allocated for caching query results. The default value is 0, which disables the query cache. Note that this amount of memory is allocated even if query_cache_type is set to 0. See Section 5.13.3, “Query Cache Configuration”, for more information.

  • query_cache_type

    Set the query cache type. Setting the GLOBAL value sets the type for all clients that connect thereafter. Individual clients can set the SESSION value to affect their own use of the query cache. Possible values are shown in the following table:

    Option Description
    0 or OFF Don't cache or retrieve results. Note that this does not deallocate the query cache buffer. To do that, you should set query_cache_size to 0.
    1 or ON Cache all query results except for those that begin with SELECT SQL_NO_CACHE.
    2 or DEMAND Cache results only for queries that begin with SELECT SQL_CACHE.

    This variable defaults to ON.

  • query_cache_wlock_invalidate

    Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing statements that read from the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of a WRITE lock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect.

  • query_prealloc_size

    The size of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.

  • range_alloc_block_size

    The size of blocks that are allocated when doing range optimization.

  • read_buffer_size

    Each thread that does a sequential scan allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072.

  • read_only

    When the variable is set to ON for a replication slave server, it causes the slave to allow no updates except from slave threads or from users that have the SUPER privilege. This can be useful to ensure that a slave server accepts updates only from its master server and not from clients. This variable does not apply to TEMPORARY tables.

  • relay_log_purge

    Disables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (ON).

  • read_rnd_buffer_size

    When reading rows in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

  • secure_auth

    If the MySQL server has been started with the --secure-auth option, it blocks connections from all accounts that have passwords stored in the old (pre-4.1) format. In that case, the value of this variable is ON, otherwise it is OFF.

    You should enable this option if you want to prevent all use of passwords employing the old format (and hence insecure communication over the network).

    Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format. See Section A.2.3, “Client does not support authentication protocol.

  • server_id

    The server ID. This value is set by the --server-id option. It is used for replication to enable master and slave servers to identify themselves uniquely.

  • shared_memory

    (Windows only.) Whether the server allows shared-memory connections.

  • shared_memory_base_name

    (Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case sensitive.

  • skip_external_locking

    This is OFF if mysqld uses external locking, ON if external locking is disabled.

  • skip_networking

    This is ON if the server allows only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. On NetWare, only TCP/IP connections are supported, so do not set this variable to ON. This variable can be set to ON with the --skip-networking option.

  • skip_show_database

    This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is allowed only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is allowed to all users, but displays the names of only those databases for which the user has the SHOW DATABASES or other privilege.

  • slave_compressed_protocol

    Whether to use compression of the slave/master protocol if both the slave and the master support it.

  • slave_load_tmpdir

    The name of the directory where the slave creates temporary files for replicating LOAD DATA INFILE statements.

  • slave_net_timeout

    The number of seconds to wait for more data from a master/slave connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory.

  • slave_skip_errors

    The replication errors that the slave should skip (ignore).

  • slave_transaction_retries

    If a replication slave SQL thread fails to execute a transaction because of an InnoDB deadlock or exceeded InnoDB's innodb_lock_wait_timeout or NDBCluster's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries slave_transaction_retries times before stopping with an error. The default value is 10.

  • slow_launch_time

    If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable.

  • socket

    On Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is /tmp/mysql.sock. (For some distribution formats, the directory might be different, such as /var/lib/mysql for RPMs.)

    On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is MySQL (not case sensitive).

  • sort_buffer_size

    Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster ORDER BY or GROUP BY operations. See Section A.4.4, “Where MySQL Stores Temporary Files”.

  • sql_mode

    The current server SQL mode, which can be set dynamically. See Section 5.2.5, “The Server SQL Mode”.

  • sql_slave_skip_counter

    The number of events from the master that a slave server should skip. See Section 13.6.2.6, “SET GLOBAL SQL_SLAVE_SKIP_COUNTER Syntax”.

  • storage_engine

    The default storage engine (table type). To set the storage engine at server startup, use the --default-storage-engine option. See Section 5.2.1, “mysqld Command Options”.

  • sync_binlog

    If the value of this variable is positive, the MySQL server synchronizes its binary log to disk (using fdatasync()) after every sync_binlog writes to the binary log. Note that there is one write to the binary log per statement if autocommit is enabled, and one write per transaction otherwise. The default value is 0, which does no synchronizing to disk. A value of 1 is the safest choice, because in the event of a crash you lose at most one statement or transaction from the binary log. However, it is also the slowest choice (unless the disk has a battery-backed cache, which makes synchronization very fast).

    If the value of sync_binlog is 0 (the default), no extra flushing is done. The server relies on the operating system to flush the file contents occasionaly as for any other file.

  • sync_frm

    If this variable is set to 1, when any non-temporary table is created its .frm file is synchronized to disk (using fdatasync()). This is slower but safer in case of a crash. The default is 1.

  • system_time_zone

    The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. Typically the time zone is specified by the TZ environment variable. It also can be specified using the --timezone option of the mysqld_safe script.

    The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the tome zone for each client that connects. See Section 5.10.8, “MySQL Server Time Zone Support”.

  • table_cache

    This is the old name of table_open_cache before MySQL 5.1.3. From 5.1.3 on, use table_open_cache instead.

  • table_definition_cache

    The number of table definitions that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. This variable was added in MySQL 5.1.3.

  • table_open_cache

    The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.2.4, “Server Status Variables”. If the value of Opened_tables is large and you don't do FLUSH TABLES a lot (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 7.4.8, “How MySQL Opens and Closes Tables”. Before MySQL 5.1.3, this variable is called table_cache.

  • table_type

    This variable is a synonym for storage_engine. In MySQL 5.1, storage_engine is the preferred name.

  • thread_cache_size

    How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. (Normally, this doesn't provide a notable performance improvement if you have a good thread implementation.) By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.2.4, “Server Status Variables”.

  • thread_concurrency

    On Solaris, mysqld calls thr_setconcurrency() with this value. This function enables applications to give the threads system a hint about the desired number of threads that should be run at the same time.

  • thread_stack

    The stack size for each thread. Many of the limits detected by the crash-me test are dependent on this value. The default is large enough for normal operation. See Section 7.1.4, “The MySQL Benchmark Suite”. The default is 192KB.

  • time_format

    This variable is not implemented.

  • time_zone

    The current time zone. This variable is used to initialize the tome zone for each client that connects. By default, the initial value of this is 'SYSTEM' (which means, “use the value of system_time_zone”). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 5.10.8, “MySQL Server Time Zone Support”.

  • tmp_table_size

    If an in-memory temporary table exceeds this size, MySQL automatically converts it to an on-disk MyISAM table. Increase the value of tmp_table_size if you do many advanced GROUP BY queries and you have lots of memory.

  • tmpdir

    The directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (‘:’) on Unix and semicolon characters (‘;’) on Windows, NetWare, and OS/2.

    The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set tmpdir to point to a directory on a memory-based filesystem or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables or LOAD DATA INFILE operations. If files in the temporary file directory are lost when the server restarts, replication fails. However, if you are using MySQL 4.0.0 or later, you can set the slave's temporary directory using the slave_load_tmpdir variable. In that case, the slave won't use the general tmpdir value and you can set tmpdir to a non-permanent location.

  • transaction_alloc_block_size

    The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

  • transaction_prealloc_size

    There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes.

    By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

  • tx_isolation

    The default transaction isolation level. Defaults to REPEATABLE-READ.

    This variable is set by the SET TRANSACTION ISOLATION LEVEL statement. See Section 13.4.6, “SET TRANSACTION Syntax”. If you set tx_isolation directly to an isolation level name that contains a space, the name should be enclosed within quotes, with the space replaced by a dash. For example:

    SET tx_isolation = 'READ-COMMITTED';
    
  • updatable_views_with_limit

    This variable controls whether updates can be made using a view that does not contain a primary key in the underlying table, if the update contains a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

    The variable can have two values:

    • 1 or YES: Issue a warning only (not an error message). This is the default value.

    • 0 or NO: Prohibit the update.

  • version

    The version number for the server.

  • version_bdb

    The BDB storage engine version.

  • version_comment

    The configure script has a --with-comment option that allows a comment to be specified when building MySQL. This variable contains the value of that comment.

  • version_compile_machine

    The type of machine or architecture on which MySQL was built.

  • version_compile_os

    The type of operating system on which MySQL was built.

  • wait_timeout

    The number of seconds the server waits for activity on a non-interactive connection before closing it. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory.

    On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.


 
 
  Published under the terms of the GNU General Public License Design by Interspire