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.

Section 5.1.4, “Session System Variables”, describes system variables that exist only as session variables (that is, they do not have any global counterpart).

Section 5.1.5, “Using System Variables”, discusses the syntax for setting and displaying system variable values.

Section 5.1.5.2, “Dynamic System Variables”, lists the variables that can be set at runtime.

Information on tuning system variables can be found in Section 7.5.2, “Tuning Server Parameters”.

Section 13.2.4, “InnoDB Startup Options and System Variables”, lists InnoDB system variables.

Section 16.4.3, “MySQL Cluster System Variables”, lists system variables which are specific to MySQL Cluster.

For information on server system variables specific to replication, see Section 15.1.2, “Replication and Binary Logging Options and Variables”.

automatic_sp_privileges

When this variable has a value of 1 (the default), the server automatically grants the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges when the creator drops the routine. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges. This variable was added in MySQL 5.0.3.

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. Relative pathnames for other variables usually are resolved relative to the base directory.

bdb_cache_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 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_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 5.2.3, “The Binary Log”.

MySQL Enterprise.  For recommendations on the optimum setting for binlog_cache_size subscribe to the MySQL Enterprise Monitor. For more information, see http://www.mysql.com/products/enterprise/advisors.html.

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. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 9.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

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_filesystem to 'utf8'. This variable was added in MySQL 5.0.19.

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:

This variable was added in MySQL 5.0.3

concurrent_insert

If 1 (the default), MySQL allows INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file. You can turn this option off by starting mysqld with --safe or --skip-new.

In MySQL 5.0.6, this variable was changed to take three integer values:

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. The default value is 10 seconds as of MySQL 5.0.52 and 5 seconds before that.

Increasing the connect_timeout value might help if clients frequently encounter errors of the form Lost connection to MySQL server at 'XXX', system error: errno.

datadir

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

date_format

This variable is unused.

datetime_format

This variable is unused.

default_week_format

The default mode value to use for the WEEK() function. See Section 11.6, “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.

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 5.1.2, “Command Options”, and Section 13.1.1, “MyISAM Startup Options”.

Note that if you enable external locking with --external-locking, there is 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 by which to increase the scale of 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 |
+----------------+

This variable was added in MySQL 5.0.6.

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 B.1.4.2, “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 systems with minimal resources.

ft_boolean_syntax

The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 11.8.2, “Boolean Full-Text Searches”.

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

ft_max_word_len

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

ft_min_word_len

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

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.

group_concat_max_len

The maximum allowed result length in bytes 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 CSV 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. This variable was added in MySQL 5.0.3.

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_isam

In MySQL 5.0, this variable appears only for reasons of backward compatibility. It is always NO because ISAM tables are no longer supported.

have_merge_engine

YES if mysqld supports MERGE tables. DISABLED if --skip-merge is used. This variable was added in MySQL 5.0.24.

have_openssl

YES if mysqld supports SSL connections, NO if not. As of MySQL 5.0.38, this variable is an alias for have_ssl.

have_query_cache

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

have_raid

In MySQL 5.0, this variable appears only for reasons of backward compatibility. It is always NO because RAID tables are no longer supported.

have_rtree_keys

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

have_ssl

YES if mysqld supports SSL connections, NO if not. This variable was added in MySQL 5.0.38. Before that, use have_openssl.

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.

hostname

The server sets this variable to the server hostname at startup. This variable was added in MySQL 5.0.38.

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.

Note that the --init-file option is unavailable if MySQL was configured with the --disable-grant-options option. See Section 2.16.2, “Typical configure Options”.

innodb_xxx

InnoDB system variables are listed in Section 13.2.4, “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.

The maximum allowable setting for join_buffer_size is 4GB.

keep_files_on_create

If a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, set the keep_files_on_create variable to ON (1), in which case MyISAM will not overwrite existing files and returns an error instead. The default value is OFF (0).

If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It will not overwrite a file in the specified directory.

This variable was added in MySQL 5.0.48.

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 on 32-bit platforms. As of MySQL 5.0.52, values larger than 4GB are allowed for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB with a warning). 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. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

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 7.2.18, “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 12.5.5, “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_files_support

Whether mysqld was compiled with options for large file support.

large_pages

Whether large page support is enabled. This variable was added in MySQL 5.0.3.

For more information, see the entry for the --large-pages server option.

large_page_size

If large page support is enabled, this shows the size of memory pages. Currently, large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. This variable was added in MySQL 5.0.3.

For more information, see the entry for the --large-pages server option.

lc_time_names

This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 9.8, “MySQL Server Locale Support”. This variable was added in MySQL 5.0.25.

license

The type of license the server has.

local_infile

Whether LOCAL is supported for LOAD DATA INFILE statements. See Section 5.3.4, “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 5.2.2, “The General Query Log”.

log_bin

Whether the binary log is enabled. See Section 5.2.3, “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 functions 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. This variable also applies to trigger creation. See Section 17.5, “Binary Logging of Stored Programs”.

This variable was added in MySQL 5.0.16.

log_bin_trust_routine_creators

This is the old name for log_bin_trust_function_creators. Before MySQL 5.0.16, it also applies to stored procedures, not just stored functions. As of 5.0.16, this variable is deprecated. It is recognized for backward compatibility but its use results in a warning.

This variable was added in MySQL 5.0.6.

log_error

The location of the error log.

log_queries_not_using_indexes

Whether queries that do not use indexes are logged to the slow query log. See Section 5.2.4, “The Slow Query Log”. This variable was added in MySQL 5.0.23.

log_slow_queries

Whether slow queries should be logged. “Slow” is determined by the value of the long_query_time variable. See Section 5.2.4, “The Slow Query Log”.

log_warnings

Whether to produce additional warning messages. It is enabled (1) by default and can be disabled by setting it to 0. 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. The default is 10. See Section 5.2.4, “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 affects only storage engines that use only table-level locking (MyISAM, MEMORY, MERGE). 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 8.2.2, “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 largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB. The value should be a multiple of 1024; non-multiples are rounded down to the nearest multiple.

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. By default, this is 100. See Section B.1.2.7, “Too many connections”, for more information.

MySQL Enterprise.  For notification that the maximum number of connections is getting dangerously high and for advice on setting the optimum value for max_connections subscribe to the MySQL Enterprise Monitor. For more information see http://www.mysql.com/products/enterprise/advisors.html.

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.

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.

For the SESSION value of this variable, the only valid values are 0 or the GLOBAL value.

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. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.

MySQL Enterprise.  Subscribers to the MySQL Enterprise Monitor receive recommendations for the optimum setting for max_heap_table_size. For more information see http://www.mysql.com/products/enterprise/advisors.html.

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_prepared_stmt_count

This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. The default value is 16,382. The allowable range of values is from 0 to 1 million. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. This variable was added in MySQL 5.0.21.

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 15.4.1, “Replication Implementation Details”.