manual.texi Use I/O consistently, not I/O sometimes and i/o sometimes.

@menu

* Manual-info::                 About This Manual

* What-is::                     What Is MySQL

* What is MySQL AB::            What Is MySQL AB

* What-is::                     What Is MySQL?

* What is MySQL AB::            What Is MySQL AB?

* Licensing and Support::       MySQL Support and Licensing

* MySQL 4.0 In A Nutshell::     MySQL 4.0 In A Nutshell

* MySQL Information Sources::   MySQL Information Sources

@node What-is, What is MySQL AB, Manual-info, Introduction

@section What Is MySQL

@section What Is MySQL?

@cindex MySQL, defined

@cindex MySQL, introduction

@node What is MySQL AB, Licensing and Support, What-is, Introduction

@section What Is MySQL AB

@section What Is MySQL AB?

@cindex MySQL AB, defined

* TODO MySQL 4.1::              Things That Should be in 4.1

* TODO future::                 Things That Must be Done in the Near Future

* TODO sometime::               Things That Have to be Done Sometime

* TODO unplanned::              Things we don't Have any Plans to do

* TODO unplanned::              Things We Have No Plans to do

@end menu

This appendix lists the features that we plan to implement in MySQL Server.

@node TODO unplanned,  , TODO sometime, TODO

@subsection Things we don't Have any Plans to do

@subsection Things We Have No Plans to do

@itemize @bullet

@item

* example-user-variables::      Using user variables

* example-Foreign keys::        Using foreign keys

* Searching on two keys::       Searching on Two Keys

* Calculating days::            Calculating visits per day

* Calculating days::            Calculating Visits Per Day

* example-AUTO_INCREMENT::      Using AUTO_INCREMENT

@end menu

@xref{UNION}.

@node Calculating days, example-AUTO_INCREMENT, Searching on two keys, Examples

@subsection Calculating visits per day

@subsection Calculating Visits Per Day

@findex BIT_OR

@findex BIT_COUNT

@node example-AUTO_INCREMENT,  , Calculating days, Examples

@subsection Using AUTO_INCREMENT

@subsection Using @code{AUTO_INCREMENT}

@cindex AUTO_INCREMENT

The @code{AUTO_INCREMENT} attribute can be used to generate an unique

@menu

* Command-line options::        mysqld Command-line Options

* Option files::                my.cnf Option Files

* Command-line options::        @code{mysqld} Command-line Options

* Option files::                @file{my.cnf} Option Files

* Installing many servers::     Installing Many Servers on the Same Machine

* Multiple servers::            Running Multiple MySQL Servers on the Same Machine

@end menu

@node Command-line options, Option files, Configuring MySQL, Configuring MySQL

@subsection mysqld Command-line Options

@subsection @code{mysqld} Command-line Options

@findex command-line options

@cindex options, command-line

@node Option files, Installing many servers, Command-line options, Configuring MySQL

@subsection my.cnf Option Files

@subsection @file{my.cnf} Option Files

@cindex default options

@cindex option files

@menu

* Secure basics::               Basics

* Secure requirements::         Requirements

* Secure GRANT::                GRANT OPTIONS

* Secure GRANT::                @code{GRANT} Options

@end menu

@node Secure basics, Secure requirements, Secure connections, Secure connections

@node Secure GRANT,  , Secure requirements, Secure connections

@subsubsection GRANT options

@subsubsection @code{GRANT} Options

@cindex SSL related options

@findex REQUIRE GRANT option

* Character sets::              The Character Set Used for Data and Sorting

* Languages::                   Non-English Error Messages

* Adding character set::        Adding a New Character Set

* Character arrays::            The character definition arrays

* Character arrays::            The Character Definition Arrays

* String collating::            String Collating Support

* Multi-byte characters::       Multi-byte Character Support

* Problems with character sets::  Problems With Character Sets

@node Character arrays, String collating, Adding character set, Localisation

@subsection The character definition arrays

@subsection The Character Definition Arrays

@code{to_lower[]} and @code{to_upper[]} are simple arrays that hold the

lowercase and uppercase characters corresponding to each member of the

@menu

* Server-Side Overview::        Overview of the Server-Side Scripts and Utilities

* safe_mysqld::                 safe_mysqld, the wrapper around mysqld

* mysqld_multi::                mysqld_multi, program for managing multiple MySQL servers

* myisampack::                  myisampack, The MySQL Compressed Read-only Table Generator

* mysqld-max::                  mysqld-max, An extended mysqld server

* safe_mysqld::                 @code{safe_mysqld}, the Wrapper Around @code{mysqld}

* mysqld_multi::                @code{mysqld_multi}, Program for Managing Multiple MySQL Servers

* myisampack::                  @code{myisampack}, The MySQL Compressed Read-only Table Generator

* mysqld-max::                  @code{mysqld-max}, An Extended @code{mysqld} Server

@end menu

@node safe_mysqld, mysqld_multi, Server-Side Overview, Server-Side Scripts

@subsection safe_mysqld, the wrapper around mysqld

@subsection @code{safe_mysqld}, the Wrapper Around @code{mysqld}

@cindex tools, safe_mysqld

@cindex scripts

@node mysqld_multi, myisampack, safe_mysqld, Server-Side Scripts

@subsection mysqld_multi, program for managing multiple MySQL servers

@subsection @code{mysqld_multi}, Program for Managing Multiple MySQL Servers

@cindex tools, mysqld_multi

@cindex scripts

@node myisampack, mysqld-max, mysqld_multi, Server-Side Scripts

@subsection myisampack, The MySQL Compressed Read-only Table Generator

@subsection @code{myisampack}, The MySQL Compressed Read-only Table Generator

@cindex compressed tables

@cindex tables, compressed

@node mysqld-max,  , myisampack, Server-Side Scripts

@subsection mysqld-max, An extended mysqld server

@subsection @code{mysqld-max}, An Extended @code{mysqld} Server

@cindex @code{mysqld-max}

@menu

* Client-Side Overview::        Overview of the Client-Side Scripts and Utilities

* mysql::                       The Command-line Tool

* mysqladmin::                  mysqladmin, Administrating a MySQL Server

* mysqladmin::                  @code{mysqladmin}, Administrating a MySQL Server

* Using mysqlcheck::            Using @code{mysqlcheck} for Table Maintenance and Crash Recovery

* mysqldump::                   mysqldump, Dumping Table Structure and Data

* mysqlhotcopy::                mysqlhotcopy, Copying MySQL Databases and Tables

* mysqlimport::                 mysqlimport, Importing Data from Text Files

* mysqldump::                   @code{mysqldump}, Dumping Table Structure and Data

* mysqlhotcopy::                @code{mysqlhotcopy}, Copying MySQL Databases and Tables

* mysqlimport::                 @code{mysqlimport}, Importing Data from Text Files

* mysqlshow::                   Showing Databases, Tables, and Columns

* perror::                      perror, Explaining Error Codes

* perror::                      @code{perror}, Explaining Error Codes

* Batch Commands::              How to Run SQL Commands from a Text File

@end menu

@node mysqladmin, Using mysqlcheck, mysql, Client-Side Scripts

@subsection mysqladmin, Administrating a MySQL Server

@subsection @code{mysqladmin}, Administrating a MySQL Server

@cindex administration, server

@cindex server administration

@node mysqldump, mysqlhotcopy, Using mysqlcheck, Client-Side Scripts

@subsection mysqldump, Dumping Table Structure and Data

@subsection @code{mysqldump}, Dumping Table Structure and Data

@cindex dumping, databases

@cindex databases, dumping

@node mysqlhotcopy, mysqlimport, mysqldump, Client-Side Scripts

@subsection mysqlhotcopy, Copying MySQL Databases and Tables

@subsection @code{mysqlhotcopy}, Copying MySQL Databases and Tables

@cindex dumping, databases

@cindex databases, dumping

@node mysqlimport, mysqlshow, mysqlhotcopy, Client-Side Scripts

@subsection mysqlimport, Importing Data from Text Files

@subsection @code{mysqlimport}, Importing Data from Text Files

@cindex importing, data

@cindex data, importing

* Replication Implementation::  Replication Implementation Overview

* Replication HOWTO::           How To Set Up Replication

* Replication Features::        Replication Features and Known Problems

* Replication Options::         Replication Options in my.cnf

* Replication Options::         Replication Options in @file{my.cnf}

* Replication SQL::             SQL Commands Related to Replication

* Replication FAQ::             Replication FAQ

* Replication Problems::        Troubleshooting Replication

@node Replication Options, Replication SQL, Replication Features, Replication

@subsection Replication Options in my.cnf

@subsection Replication Options in @file{my.cnf}

If you are using replication, we recommend you to use MySQL Version

3.23.30 or later. Older versions work, but they do have some bugs and are

* InnoDB transaction model::    InnoDB Transaction Model.

* Implementation::              Implementation of Multi-versioning

* Table and index::             Table and Index Structures

* File space management::       File Space Management and Disk i/o

* File space management::       File Space Management and Disk I/O

* Error handling::              Error Handling

* InnoDB restrictions::         Restrictions on InnoDB Tables

* InnoDB contact information::  InnoDB Contact Information.

data is very often beneficial for performance.

You can also use @strong{raw disk partitions} (raw devices)

as data files. In some Unixes

they speed up i/o. See the manual section on InnoDB file space management 

they speed up I/O. See the manual section on InnoDB file space management 

about how to specify them in @file{my.cnf}.

@strong{Warning:} on Linux x86 you must be careful you @strong{do not set memory usage

where n is the number of log files in the group. The

bigger the value,

the less checkpoint flush activity is needed in the buffer pool,

saving disk i/o. But bigger log files also mean that recovery will be

saving disk I/O. But bigger log files also mean that recovery will be

slower in case of a crash. The combined size of log files must

be < 4 GB on 32-bit computers.

@item @code{innodb_log_buffer_size} @tab

on disk.  Sensible values range from 1M to half the combined size of log

files. A big log buffer allows large transactions to run without a need

to write the log to disk until the transaction commit. Thus, if you have

big transactions, making the log buffer big will save disk i/o.

big transactions, making the log buffer big will save disk I/O.

@item @code{innodb_flush_log_at_trx_commit} @tab

Normally this is set to 1, meaning that at a transaction commit the log

is flushed to disk, and the modifications made by the transaction become

permanent, and survive a database crash. If you are willing to

compromise this safety, and you are running small transactions, you may

set this to 0 to reduce disk i/o to the logs.

set this to 0 to reduce disk I/O to the logs.

@item @code{innodb_log_arch_dir} @tab

The directory where fully written log files would be archived if we used

log archiving.  The value of this parameter should currently be set the

archive InnoDB log files.

@item @code{innodb_buffer_pool_size} @tab

The size of the memory buffer InnoDB uses to cache data and indexes of

its tables.  The bigger you set this the less disk i/o is needed to

its tables.  The bigger you set this the less disk I/O is needed to

access data in tables. On a dedicated database server you may set this

parameter up to 80 % of the machine physical memory size. Do not set it

too large, though, because competition of the physical memory may cause

will start to allocate memory from the operating system, and write

warning messages to the MySQL error log.

@item @code{innodb_file_io_threads} @tab

Number of file i/o threads in InnoDB. Normally, this should be 4, but

on Windows disk i/o may benefit from a larger number.

Number of file I/O threads in InnoDB. Normally, this should be 4, but

on Windows disk I/O may benefit from a larger number.

@item @code{innodb_lock_wait_timeout} @tab

Timeout in seconds an InnoDB transaction may wait for a lock before

being rolled back.  InnoDB automatically detects transaction deadlocks

During the conversion of big tables you should set the InnoDB

buffer pool size big

to reduce disk i/o. Not bigger than 80 % of the physical memory, though.

to reduce disk I/O. Not bigger than 80 % of the physical memory, though.

You should set InnoDB log files big, and also the log buffer large.

Make sure you do not run out of tablespace: InnoDB tables take a lot

of space, it will start a rollback, and that can take hours if it is

disk-bound.

In inserts InnoDB uses the insert buffer to merge secondary index records

to indexes in batches. That saves a lot of disk i/o. In rollback no such

to indexes in batches. That saves a lot of disk I/O. In rollback no such

mechanism is used, and the rollback can take 30 times longer than the

insertion.

database,

it is better that you kill the database process and delete all InnoDB data

and log files and all InnoDB table @file{.frm} files, and start

your job again, rather than wait for millions of disk i/os to complete.

your job again, rather than wait for millions of disk I/Os to complete.

@subsubsection  Foreign Key Constraints

modified database pages to disk.

The above explains why making your log files very big may save

disk i/o in checkpointing. It can make sense to set

disk I/O in checkpointing. It can make sense to set

the total size of the log files as big as the buffer pool or even bigger.

The drawback in big log files is that crash recovery can last longer

because there will be more log to apply to the database.

@strong{8.}

Beware of big rollbacks of mass inserts: InnoDB uses the insert buffer

to save disk i/o in inserts, but in a corresponding rollback no such

to save disk I/O in inserts, but in a corresponding rollback no such

mechanism is used. A disk-bound rollback can take 30 times the time

of the corresponding insert. Killing the database process will not

help because the rollback will start again at the database startup. The

@item

semaphore waits of threads,

@item

pending file i/o requests,

pending file I/O requests,

@item

buffer pool statistics, and

@item

for a semaphore and statistics on how many times

threads have needed a spin or a wait on a mutex or

a rw-lock semaphore. A big number of threads waiting

for semaphores may be a result of disk i/o, or

for semaphores may be a result of disk I/O, or

contention problems inside InnoDB. Contention can be

due to heavy parallelism of queries, or problems in

operating system thread scheduling.

@item

Section CURRENT PENDING FILE I/O'S lists pending

file i/o requests. A large number of these indicates

that the workload is disk i/o -bound.

file I/O requests. A large number of these indicates

that the workload is disk I/O-bound.

@item

Section BUFFER POOL gives you statistics

on pages read and written. You can calculate from these

numbers how many data file i/o's your queries are

numbers how many data file I/Os your queries are

currently doing.

@end itemize

the row data will be on the same page where the index search

leads us. In many databases the data is traditionally stored on a different

page from the index record. If a table is large, the clustered

index architecture often saves a disk i/o when compared to the

index architecture often saves a disk I/O when compared to the

traditional solution.

The records in non-clustered indexes (we also call them secondary indexes),

On the other hand, secondary indexes are usually non-unique and

insertions happen in a relatively random order into secondary indexes.

This would cause a lot of random disk i/o's without a special mechanism

This would cause a lot of random disk I/Os without a special mechanism

used in InnoDB.

If an index record should be inserted to a non-unique secondary index,

The insert buffer is periodically merged to the secondary index

trees in the database. Often we can merge several insertions on the

same page in of the index tree, and hence save disk i/o's.

same page in of the index tree, and hence save disk I/Os.

It has been measured that the insert buffer can speed up insertions

to a table up to 15 times.

@node File space management, Error handling, Table and index, InnoDB

@subsection File Space Management and Disk i/o

@subsection File Space Management and Disk I/O

@menu

* InnoDB Disk i/o::             Disk i/o

* InnoDB Disk i/o::             Disk I/O

* InnoDB File space::           File Space Management

* InnoDB File Defragmenting::   Defragmenting a Table

@end menu

@node InnoDB Disk i/o, InnoDB File space, File space management, File space management

@subsubsection Disk i/o

@subsubsection Disk I/O

In disk i/o InnoDB uses asynchronous i/o. On Windows NT

it uses the native asynchronous i/o provided by the operating system.

On Unix, InnoDB uses simulated asynchronous i/o built

into InnoDB: InnoDB creates a number of i/o threads to take care

of i/o operations, such as read-ahead. In a future version we will

In disk I/O InnoDB uses asynchronous I/O. On Windows NT

it uses the native asynchronous I/O provided by the operating system.

On Unix, InnoDB uses simulated asynchronous I/O built

into InnoDB: InnoDB creates a number of I/O threads to take care

of I/O operations, such as read-ahead. In a future version we will

add support for simulated aio on Windows NT and native aio on those

versions of Unix which have one.

On Windows NT InnoDB uses non-buffered i/o. That means that the disk

On Windows NT InnoDB uses non-buffered I/O. That means that the disk

pages InnoDB reads or writes are not buffered in the operating system

file cache. This saves some memory bandwidth.

innodb_data_file_path=hdd1:5Graw;hdd2:2Graw

@end example

By using a raw disk you can on some Unixes perform unbuffered i/o.

By using a raw disk you can on some Unixes perform unbuffered I/O.

There are two read-ahead heuristics in InnoDB: sequential read-ahead

and random read-ahead. In sequential read-ahead InnoDB notices that

the access pattern to a segment in the tablespace is sequential.

Then InnoDB will post in advance a batch of reads of database pages to the

i/o system. In random read-ahead InnoDB notices that some area

I/O system. In random read-ahead InnoDB notices that some area

in a tablespace seems to be in the process of being

fully read into the buffer pool. Then InnoDB posts the remaining

reads to the i/o system.

reads to the I/O system.

@node InnoDB File space, InnoDB File Defragmenting, InnoDB Disk i/o, File space management

@itemize @bullet

@item

Added @code{SLAVE START} and @code{SLAVE STOP} statements.

@item

Added @code{TYPE=QUICK} option to @code{CHECK} and to @code{REPAIR}.

@item

Fixed bug in @code{REPAIR TABLE} when the table was in use by other threads.