path: root/man/myisamchk.1

'\" t
.\"
.TH "\FBMYISAMCHK\FR" "1" "15 May 2020" "MariaDB 10\&.6" "MariaDB Database System"
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.\" myisamchk
.SH "NAME"
myisamchk \- MyISAM table\-maintenance utility
.SH "SYNOPSIS"
.HP \w'\fBmyisamchk\ [\fR\fB\fIoptions\fR\fR\fB]\ \fR\fB\fItbl_name\fR\fR\fB\ \&.\&.\&.\fR\ 'u
\fBmyisamchk [\fR\fB\fIoptions\fR\fR\fB] \fR\fB\fItbl_name\fR\fR\fB \&.\&.\&.\fR
.SH "DESCRIPTION"
.PP
The
\fBmyisamchk\fR
utility gets information about your database tables or checks, repairs, or optimizes them\&.
\fBmyisamchk\fR
works with
MyISAM
tables (tables that have
\&.MYD
and
\&.MYI
files for storing data and indexes)\&.
.PP
The use of
\fBmyisamchk\fR
with partitioned tables is not supported\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBCaution\fR
.ps -1
.br
.PP
It is best to make a backup of a table before performing a table repair operation; under some circumstances the operation might cause data loss\&. Possible causes include but are not limited to file system errors\&.
.sp .5v
.RE
.PP
Invoke
\fBmyisamchk\fR
like this:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk [\fR\fB\fIoptions\fR\fR\fB] \fR\fB\fItbl_name\fR\fR\fB \&.\&.\&.\fR
.fi
.if n \{\
.RE
.\}
.PP
The
\fIoptions\fR
specify what you want
\fBmyisamchk\fR
to do\&. They are described in the following sections\&. You can also get a list of options by invoking
\fBmyisamchk \-\-help\fR\&.
.PP
With no options,
\fBmyisamchk\fR
simply checks your table as the default operation\&. To get more information or to tell
\fBmyisamchk\fR
to take corrective action, specify options as described in the following discussion\&.
.PP
\fItbl_name\fR
is the database table you want to check or repair\&. If you run
\fBmyisamchk\fR
somewhere other than in the database directory, you must specify the path to the database directory, because
\fBmyisamchk\fR
has no idea where the database is located\&. In fact,
\fBmyisamchk\fR
does not actually care whether the files you are working on are located in a database directory\&. You can copy the files that correspond to a database table into some other location and perform recovery operations on them there\&.
.PP
You can name several tables on the
\fBmyisamchk\fR
command line if you wish\&. You can also specify a table by naming its index file (the file with the
\&.MYI
suffix)\&. This allows you to specify all tables in a directory by using the pattern
*\&.MYI\&. For example, if you are in a database directory, you can check all the
MyISAM
tables in that directory like this:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk *\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
If you are not in the database directory, you can check all the tables there by specifying the path to the directory:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \fR\fB\fI/path/to/database_dir/\fR\fR\fB*\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
You can even check all tables in all databases by specifying a wildcard with the path to the MariaDB data directory:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \fR\fB\fI/path/to/datadir/*/*\fR\fR\fB\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
The recommended way to quickly check all
MyISAM
tables is:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \-\-silent \-\-fast \fR\fB\fI/path/to/datadir/*/*\fR\fR\fB\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
If you want to check all
MyISAM
tables and repair any that are corrupted, you can use the following command:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \-\-silent \-\-force \-\-fast \-\-update\-state \e\fR
          \fB\-\-key_buffer_size=64M \-\-sort_buffer_size=64M \e\fR
          \fB\-\-read_buffer_size=1M \-\-write_buffer_size=1M \e\fR
          \fB\fI/path/to/datadir/*/*\fR\fR\fB\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
This command assumes that you have more than 64MB free\&. For more information about memory allocation with
\fBmyisamchk\fR, see
the section called \(lqMYISAMCHK MEMORY USAGE\(rq\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBImportant\fR
.ps -1
.br
.PP
\fIYou must ensure that no other program is using the tables while you are running \fR\fI\fBmyisamchk\fR\fR\&. The most effective means of doing so is to shut down the MariaDB server while running
\fBmyisamchk\fR, or to lock all tables that
\fBmyisamchk\fR
is being used on\&.
.PP
Otherwise, when you run
\fBmyisamchk\fR, it may display the following error message:
.sp
.if n \{\
.RS 4
.\}
.nf
warning: clients are using or haven\'t closed the table properly
.fi
.if n \{\
.RE
.\}
.PP
This means that you are trying to check a table that has been updated by another program (such as the
\fBmysqld\fR
server) that hasn\'t yet closed the file or that has died without closing the file properly, which can sometimes lead to the corruption of one or more
MyISAM
tables\&.
.PP
If
\fBmysqld\fR
is running, you must force it to flush any table modifications that are still buffered in memory by using
FLUSH TABLES\&. You should then ensure that no one is using the tables while you are running
\fBmyisamchk\fR
.PP
However, the easiest way to avoid this problem is to use
CHECK TABLE
instead of
\fBmyisamchk\fR
to check tables\&.
.sp .5v
.RE
.PP
\fBmyisamchk\fR
supports the following options, which can be specified on the command line or in the
[myisamchk]
option file group\&.
.SH "MYISAMCHK GENERAL OPTIONS"
.\" options: myisamchk
.\" myisamchk: options
.PP
The options described in this section can be used for any type of table maintenance operation performed by
\fBmyisamchk\fR\&. The sections following this one describe options that pertain only to specific operations, such as table checking or repairing\&.
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: help option
.\" help option: myisamchk
\fB\-\-help\fR,
\fB\-?\fR
.sp
Display a help message and exit\&. Options are grouped by type of operation\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: HELP option
.\" HELP option: myisamchk
\fB\-\-HELP\fR,
\fB\-H\fR
.sp
Display a help message and exit\&. Options are presented in a single list\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: debug option
.\" debug option: myisamchk
\fB\-\-debug=\fR\fB\fIdebug_options\fR\fR,
\fB\-# \fR\fB\fIdebug_options\fR\fR
.sp
Write a debugging log\&. A typical
\fIdebug_options\fR
string is
\'d:t:o,\fIfile_name\fR\'\&. The default is
\'d:t:o,/tmp/myisamchk\&.trace\'\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: silent option
.\" silent option: myisamchk
\fB\-\-silent\fR,
\fB\-s\fR
.sp
Silent mode\&. Write output only when errors occur\&. You can use
\fB\-s\fR
twice (\fB\-ss\fR) to make
\fBmyisamchk\fR
very silent\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: verbose option
.\" verbose option: myisamchk
\fB\-\-verbose\fR,
\fB\-v\fR
.sp
Verbose mode\&. Print more information about what the program does\&. This can be used with
\fB\-d\fR
and
\fB\-e\fR\&. Use
\fB\-v\fR
multiple times (\fB\-vv\fR,
\fB\-vvv\fR) for even more output\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: version option
.\" version option: myisamchk
\fB\-\-version\fR,
\fB\-V\fR
.sp
Display version information and exit\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: wait option
.\" wait option: myisamchk
\fB\-\-wait\fR,
\fB\-w\fR
.sp
Instead of terminating with an error if the table is locked, wait until the table is unlocked before continuing\&. If you are running
\fBmysqld\fR
with external locking disabled, the table can be locked only by another
\fBmyisamchk\fR
command\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: print argument list option
.\" print argument list option: myisamchk
\fB\-\-print\-defaults\fR
.sp
Print the program argument list and exit\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: no defaults option
.\" no defaults option: myisamchk
\fB\-\-no\-defaults\fR
.sp
Don't read default options from any option file\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: defaults file option
.\" defaults file option: myisamchk
\fB\-\-defaults\-file=#\fR
.sp
Only read default options from the given file\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: defaults extrafile option
.\" defaults extra file option: myisamchk
\fB\-\-defaults\-extra\-file=#\fR
.sp
Read this file after the global files are read\&.
.RE
.PP
You can also set the following variables by using
\fB\-\-\fR\fB\fIvar_name\fR\fR\fB=\fR\fB\fIvalue\fR\fR
syntax:
.\" decode_bits myisamchk variable
.\" ft_max_word_len myisamchk variable
.\" ft_min_word_len myisamchk variable
.\" ft_stopword_file myisamchk variable
.\" key_buffer_size myisamchk variable
.\" key_cache_block_size myisamchk variable
.\" myisam_block_size myisamchk variable
.\" read_buffer_size myisamchk variable
.\" sort_buffer_size myisamchk variable
.\" sort_key_blocks myisamchk variable
.\" stats_method myisamchk variable
.\" write_buffer_size myisamchk variable
.TS
allbox tab(:);
l l
l l
l l
l l
l l
l l
l l
l l
l l
l l
l l
l l.
T{
\fBVariable\fR
T}:T{
\fBDefault Value\fR
T}
T{
decode_bits
T}:T{
9
T}
T{
ft_max_word_len
T}:T{
version\-dependent
T}
T{
ft_min_word_len
T}:T{
4
T}
T{
ft_stopword_file
T}:T{
built\-in list
T}
T{
key_buffer_size
T}:T{
523264
T}
T{
key_cache_block_size
T}:T{
1024
T}
T{
myisam_block_size
T}:T{
1024
T}
T{
read_buffer_size
T}:T{
262136
T}
T{
sort_buffer_size
T}:T{
2097144
T}
T{
sort_key_blocks
T}:T{
16
T}
T{
stats_method
T}:T{
nulls_unequal
T}
T{
write_buffer_size
T}:T{
262136
T}
.TE
.sp 1
.PP
The possible
\fBmyisamchk\fR
variables and their default values can be examined with
\fBmyisamchk \-\-help\fR:
.PP
sort_buffer_size
is used when the keys are repaired by sorting keys, which is the normal case when you use
\fB\-\-recover\fR\&.
.PP
key_buffer_size
is used when you are checking the table with
\fB\-\-extend\-check\fR
or when the keys are repaired by inserting keys row by row into the table (like when doing normal inserts)\&. Repairing through the key buffer is used in the following cases:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
You use
\fB\-\-safe\-recover\fR\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
The temporary files needed to sort the keys would be more than twice as big as when creating the key file directly\&. This is often the case when you have large key values for
CHAR,
VARCHAR, or
TEXT
columns, because the sort operation needs to store the complete key values as it proceeds\&. If you have lots of temporary space and you can force
\fBmyisamchk\fR
to repair by sorting, you can use the
\fB\-\-sort\-recover\fR
option\&.
.RE
.PP
Repairing through the key buffer takes much less disk space than using sorting, but is also much slower\&.
.PP
If you want a faster repair, set the
key_buffer_size
and
sort_buffer_size
variables to about 25% of your available memory\&. You can set both variables to large values, because only one of them is used at a time\&.
.PP
myisam_block_size
is the size used for index blocks\&.
.PP
stats_method
influences how
NULL
values are treated for index statistics collection when the
\fB\-\-analyze\fR
option is given\&. It acts like the
myisam_stats_method
system variable\&. For more information, see the description of
myisam_stats_method
in
Section\ \&5.1.4, \(lqServer System Variables\(rq, and
Section\ \&7.4.7, \(lqMyISAM Index Statistics Collection\(rq\&.
.PP
ft_min_word_len
and
ft_max_word_len
indicate the minimum and maximum word length for
FULLTEXT
indexes\&.
ft_stopword_file
names the stopword file\&. These need to be set under the following circumstances\&.
.PP
If you use
\fBmyisamchk\fR
to perform an operation that modifies table indexes (such as repair or analyze), the
FULLTEXT
indexes are rebuilt using the default full\-text parameter values for minimum and maximum word length and the stopword file unless you specify otherwise\&. This can result in queries failing\&.
.PP
The problem occurs because these parameters are known only by the server\&. They are not stored in
MyISAM
index files\&. To avoid the problem if you have modified the minimum or maximum word length or the stopword file in the server, specify the same
ft_min_word_len,
ft_max_word_len, and
ft_stopword_file
values to
\fBmyisamchk\fR
that you use for
\fBmysqld\fR\&. For example, if you have set the minimum word length to 3, you can repair a table with
\fBmyisamchk\fR
like this:
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \-\-recover \-\-ft_min_word_len=3 \fR\fB\fItbl_name\fR\fR\fB\&.MYI\fR
.fi
.if n \{\
.RE
.\}
.PP
To ensure that
\fBmyisamchk\fR
and the server use the same values for full\-text parameters, you can place each one in both the
[mysqld]
and
[myisamchk]
sections of an option file:
.sp
.if n \{\
.RS 4
.\}
.nf
[mysqld]
ft_min_word_len=3
[myisamchk]
ft_min_word_len=3
.fi
.if n \{\
.RE
.\}
.PP
An alternative to using
\fBmyisamchk\fR
is to use the
REPAIR TABLE,
ANALYZE TABLE,
OPTIMIZE TABLE, or
ALTER TABLE\&. These statements are performed by the server, which knows the proper full\-text parameter values to use\&.
.SH "MYISAMCHK CHECK OPTIONS"
.\" check options: myisamchk
.\" tables: checking
.PP
\fBmyisamchk\fR
supports the following options for table checking operations:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: check option
.\" check option: myisamchk
\fB\-\-check\fR,
\fB\-c\fR
.sp
Check the table for errors\&. This is the default operation if you specify no option that selects an operation type explicitly\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: check-only-changed option
.\" check-only-changed option: myisamchk
\fB\-\-check\-only\-changed\fR,
\fB\-C\fR
.sp
Check only tables that have changed since the last check\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: extend-check option
.\" extend-check option: myisamchk
\fB\-\-extend\-check\fR,
\fB\-e\fR
.sp
Check the table very thoroughly\&. This is quite slow if the table has many indexes\&. This option should only be used in extreme cases\&. Normally,
\fBmyisamchk\fR
or
\fBmyisamchk \-\-medium\-check\fR
should be able to determine whether there are any errors in the table\&.
.sp
If you are using
\fB\-\-extend\-check\fR
and have plenty of memory, setting the
key_buffer_size
variable to a large value helps the repair operation run faster\&.
.sp
For a description of the output format, see
the section called \(lqMYISAMCHK TABLE INFORMATION\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: fast option
.\" fast option: myisamchk
\fB\-\-fast\fR,
\fB\-F\fR
.sp
Check only tables that haven\'t been closed properly\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: force option
.\" force option: myisamchk
\fB\-\-force\fR,
\fB\-f\fR
.sp
Do a repair operation automatically if
\fBmyisamchk\fR
finds any errors in the table\&. The repair type is the same as that specified with the
\fB\-\-recover\fR
or
\fB\-r\fR
option\&. States will be updated as with 
\fB\-\-update\-state\fR\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: information option
.\" information option: myisamchk
\fB\-\-information\fR,
\fB\-i\fR
.sp
Print informational statistics about the table that is checked\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: medium-check option
.\" medium-check option: myisamchk
\fB\-\-medium\-check\fR,
\fB\-m\fR
.sp
Do a check that is faster than an
\fB\-\-extend\-check\fR
operation\&. This finds only 99\&.99% of all errors, which should be good enough in most cases\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: read-only option
.\" read-only option: myisamchk
\fB\-\-read\-only\fR,
\fB\-T\fR
.sp
Do not mark the table as checked\&. This is useful if you use
\fBmyisamchk\fR
to check a table that is in use by some other application that does not use locking, such as
\fBmysqld\fR
when run with external locking disabled\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: update-state option
.\" update-state option: myisamchk
\fB\-\-update\-state\fR,
\fB\-U\fR
.sp
Store information in the
\&.MYI
file to indicate when the table was checked and whether the table crashed\&. This should be used to get full benefit of the
\fB\-\-check\-only\-changed\fR
option, but you shouldn\'t use this option if the
\fBmysqld\fR
server is using the table and you are running it with external locking disabled\&.
.RE
.SH "MYISAMCHK REPAIR OPTIONS"
.\" repair options: myisamchk
.\" files: repairing
.PP
\fBmyisamchk\fR
supports the following options for table repair operations (operations performed when an option such as
\fB\-\-recover\fR
or
\fB\-\-safe\-recover\fR
is given):
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: backup option
.\" backup option: myisamchk
\fB\-\-backup\fR,
\fB\-B\fR
.sp
Make a backup of the
\&.MYD
file as
\fIfile_name\fR\-\fItime\fR\&.BAK
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: character-sets-dir option
.\" character-sets-dir option: myisamchk
\fB\-\-character\-sets\-dir=\fR\fB\fIpath\fR\fR
.sp
The directory where character sets are installed\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: correct-checksum option
.\" correct-checksum option: myisamchk
\fB\-\-correct\-checksum\fR
.sp
Correct the checksum information for the table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: create-missing-keys option
.\" create-missing-keys option: myisamchk
\fB\-\-create\-missing\-keys\fR
.sp
Create missing keys. This assumes that the data file is correct and that the 
number of rows stored in the index file is correct\&. Enables 
\fB\-\-quick\fR\&.

.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: data-file-length option
.\" data-file-length option: myisamchk
\fB\-\-data\-file\-length=\fR\fB\fIlen\fR\fR,
\fB\-D \fR\fB\fIlen\fR\fR
.sp
The maximum length of the data file (when re\-creating data file when it is
\(lqfull\(rq)\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: extend-check option
.\" extend-check option: myisamchk
\fB\-\-extend\-check\fR,
\fB\-e\fR
.sp
Do a repair that tries to recover every possible row from the data file\&. Normally, this also finds a lot of garbage rows\&. Do not use this option unless you are desperate\&.
.sp
For a description of the output format, see
the section called \(lqMYISAMCHK TABLE INFORMATION\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: force option
.\" force option: myisamchk
\fB\-\-force\fR,
\fB\-f\fR
.sp
Overwrite old intermediate files (files with names like
\fItbl_name\fR\&.TMD) instead of aborting\&. Add another
\fB\-\-force\fR
to avoid 'myisam_sort_buffer_size is too small' errors\&. In this case 
we will attempt to do the repair with the given 
\fBmyisam_sort_buffer_size\fR
and dynamically allocate as many management buffers as needed\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: keys-used option
.\" keys-used option: myisamchk
\fB\-\-keys\-used=\fR\fB\fIval\fR\fR,
\fB\-k \fR\fB\fIval\fR\fR
.sp
For
\fBmyisamchk\fR, the option value is a bit\-value that indicates which indexes to update\&. Each binary bit of the option value corresponds to a table index, where the first index is bit 0\&. An option value of 0 disables updates to all indexes, which can be used to get faster inserts\&. Deactivated indexes can be reactivated by using
\fBmyisamchk \-r\fR\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: max-record-length option
.\" max-record-length option: myisamchk
\fB\-\-max\-record\-length=\fR\fB\fIlen\fR\fR
.sp
Skip rows larger than the given length if
\fBmyisamchk\fR
cannot allocate memory to hold them\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: parallel-recover option
.\" parallel-recover option: myisamchk
\fB\-\-parallel\-recover\fR,
\fB\-p\fR
.sp
Use the same technique as
\fB\-r\fR
and
\fB\-n\fR, but create all the keys in parallel, using different threads\&.
\fIThis is beta\-quality code\&. Use at your own risk!\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: quick option
.\" quick option: myisamchk
\fB\-\-quick\fR,
\fB\-q\fR
.sp
Achieve a faster repair by modifying only the index file, not the data file\&. You can specify this option twice to force
\fBmyisamchk\fR
to modify the original data file in case of duplicate keys\&. NOTE: Tables where the data file is corrupted can't be fixed with this option\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: recover option
.\" recover option: myisamchk
\fB\-\-recover\fR,
\fB\-r\fR
.sp
Do a repair that can fix almost any problem except unique keys that are not unique (which is an extremely unlikely error with
MyISAM
tables)\&. If you want to recover a table, this is the option to try first\&. You should try
\fB\-\-safe\-recover\fR
only if
\fBmyisamchk\fR
reports that the table cannot be recovered using
\fB\-\-recover\fR\&. (In the unlikely case that
\fB\-\-recover\fR
fails, the data file remains intact\&.)
.sp
If you have lots of memory, you should increase the value of
sort_buffer_size\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: safe-recover option
.\" safe-recover option: myisamchk
\fB\-\-safe\-recover\fR,
\fB\-o\fR
.sp
Do a repair using an old recovery method that reads through all rows in order and updates all index trees based on the rows found\&. This is an order of magnitude slower than
\fB\-\-recover\fR, but can handle a couple of very unlikely cases that
\fB\-\-recover\fR
cannot\&. This recovery method also uses much less disk space than
\fB\-\-recover\fR\&. Normally, you should repair first using
\fB\-\-recover\fR, and then with
\fB\-\-safe\-recover\fR
only if
\fB\-\-recover\fR
fails\&.
.sp
If you have lots of memory, you should increase the value of
key_buffer_size\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: set-collation option
.\" set-collation option: myisamchk
\fB\-\-set\-collation=\fR\fB\fIname\fR\fR
.sp
Specify the collation to use for sorting table indexes\&. The character set name is implied by the first part of the collation name\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: sort-recover option
.\" sort-recover option: myisamchk
\fB\-\-sort\-recover\fR,
\fB\-n\fR
.sp
Force
\fBmyisamchk\fR
to use sorting to resolve the keys even if the temporary files would be very large\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: tmpdir option
.\" tmpdir option: myisamchk
\fB\-\-tmpdir=\fR\fB\fIpath\fR\fR,
\fB\-t \fR\fB\fIpath\fR\fR
.sp
The path of the directory to be used for storing temporary files\&. If this is not set,
\fBmyisamchk\fR
uses the value of the
TMPDIR
environment variable\&.
tmpdir
can be set to a list of directory paths that are used successively in round\-robin fashion for creating temporary files\&. The separator character between directory names is the colon (\(lq:\(rq) on Unix and the semicolon (\(lq;\(rq) on Windows, NetWare, and OS/2\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: unpack option
.\" unpack option: myisamchk
\fB\-\-unpack\fR,
\fB\-u\fR
.sp
Unpack a table that was packed with
\fBmyisampack\fR\&.
.RE
.SH "OTHER MYISAMCHK OPTIONS"
.PP
\fBmyisamchk\fR
supports the following options for actions other than table checks and repairs:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: analyze option
.\" analyze option: myisamchk
\fB\-\-analyze\fR,
\fB\-a\fR
.sp
Analyze the distribution of key values\&. This improves join performance by enabling the join optimizer to better choose the order in which to join the tables and which indexes it should use\&. To obtain information about the key distribution, use a
\fBmyisamchk \-\-description \-\-verbose \fR\fB\fItbl_name\fR\fR
command or the
SHOW INDEX FROM \fItbl_name\fR
statement\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: block-search option
.\" block-search option: myisamchk
\fB\-\-block\-search=\fR\fB\fIoffset\fR\fR,
\fB\-b \fR\fB\fIoffset\fR\fR
.sp
Find the record that a block at the given offset belongs to\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: description option
.\" description option: myisamchk
\fB\-\-description\fR,
\fB\-d\fR
.sp
Print some descriptive information about the table\&. Specifying the
\fB\-\-verbose\fR
option once or twice produces additional information\&. See
the section called \(lqMYISAMCHK TABLE INFORMATION\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: set-auto-increment[ option
.\" set-auto-increment[ option: myisamchk
\fB\-\-set\-auto\-increment[=\fR\fB\fIvalue\fR\fR\fB]\fR,
\fB\-A[\fR\fB\fIvalue\fR\fR\fB]\fR
.sp
Force
AUTO_INCREMENT
numbering for new records to start at the given value (or higher, if there are existing records with
AUTO_INCREMENT
values this large)\&. If
\fIvalue\fR
is not specified,
AUTO_INCREMENT
numbers for new records begin with the largest value currently in the table, plus one\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: sort-index option
.\" sort-index option: myisamchk
\fB\-\-sort\-index\fR,
\fB\-S\fR
.sp
Sort the index tree blocks in high\-low order\&. This optimizes seeks and makes table scans that use indexes faster\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: sort-records option
.\" sort-records option: myisamchk
\fB\-\-sort\-records=\fR\fB\fIN\fR\fR,
\fB\-R \fR\fB\fIN\fR\fR
.sp
Sort records according to a particular index\&. This makes your data much more localized and may speed up range\-based
SELECT
and
ORDER BY
operations that use this index\&. (The first time you use this option to sort a table, it may be very slow\&.) To determine a table\'s index numbers, use
SHOW INDEX, which displays a table\'s indexes in the same order that
\fBmyisamchk\fR
sees them\&. Indexes are numbered beginning with 1\&.
.sp
If keys are not packed (PACK_KEYS=0), they have the same length, so when
\fBmyisamchk\fR
sorts and moves records, it just overwrites record offsets in the index\&. If keys are packed (PACK_KEYS=1),
\fBmyisamchk\fR
must unpack key blocks first, then re\-create indexes and pack the key blocks again\&. (In this case, re\-creating indexes is faster than updating offsets for each index\&.)
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
.\" myisamchk: stats_method option
.\" stats_method option: myisamchk
\fB\-\-stats\-method=name\fR
.sp
Specifies how index statistics collection code should treat NULLs\&. Possible values 
of name are "nulls_unequal" (default), "nulls_equal" (emulate MySQL 4 behavior), and "nulls_ignored"\&.
.RE
.SH "MYISAMCHK TABLE INFORMATION"
.\" table description: myisamchk
.\" tables: information
.\" examples: myisamchk output
.\" myisamchk: example output
.PP
To obtain a description of a
MyISAM
table or statistics about it, use the commands shown here\&. The output from these commands is explained later in this section\&.
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
\fBmyisamchk \-d \fR\fB\fItbl_name\fR\fR
.sp
Runs
\fBmyisamchk\fR
in
\(lqdescribe mode\(rq
to produce a description of your table\&. If you start the MariaDB server with external locking disabled,
\fBmyisamchk\fR
may report an error for a table that is updated while it runs\&. However, because
\fBmyisamchk\fR
does not change the table in describe mode, there is no risk of destroying data\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
\fBmyisamchk \-dv \fR\fB\fItbl_name\fR\fR
.sp
Adding
\fB\-v\fR
runs
\fBmyisamchk\fR
in verbose mode so that it produces more information about the table\&. Adding
\fB\-v\fR
a second time produces even more information\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
\fBmyisamchk \-eis \fR\fB\fItbl_name\fR\fR
.sp
Shows only the most important information from a table\&. This operation is slow because it must read the entire table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
\fBmyisamchk \-eiv \fR\fB\fItbl_name\fR\fR
.sp
This is like
\fB\-eis\fR, but tells you what is being done\&.
.RE
.PP
The
\fItbl_name\fR
argument can be either the name of a
MyISAM
table or the name of its index file, as described in
\fBmyisamchk\fR(1)\&. Multiple
\fItbl_name\fR
arguments can be given\&.
.PP
Suppose that a table named
person
has the following structure\&. (The
MAX_ROWS
table option is included so that in the example output from
\fBmyisamchk\fR
shown later, some values are smaller and fit the output format more easily\&.)
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE TABLE person
(
  id         INT NOT NULL AUTO_INCREMENT,
  last_name  VARCHAR(20) NOT NULL,
  first_name VARCHAR(20) NOT NULL,
  birth      DATE,
  death      DATE,
  PRIMARY KEY (id),
  INDEX (last_name, first_name),
  INDEX (birth)
) MAX_ROWS = 1000000;
.fi
.if n \{\
.RE
.\}
.PP
Suppose also that the table has these data and index file sizes:
.sp
.if n \{\
.RS 4
.\}
.nf
\-rw\-rw\-\-\-\-  1 mysql  mysql  9347072 Aug 19 11:47 person\&.MYD
\-rw\-rw\-\-\-\-  1 mysql  mysql  6066176 Aug 19 11:47 person\&.MYI
.fi
.if n \{\
.RE
.\}
.PP
Example of
\fBmyisamchk \-dvv\fR
output:
.sp
.if n \{\
.RS 4
.\}
.nf
MyISAM file:         person
Record format:       Packed
Character set:       latin1_swedish_ci (8)
File\-version:        1
Creation time:       2009\-08\-19 16:47:41
Recover time:        2009\-08\-19 16:47:56
Status:              checked,analyzed,optimized keys
Auto increment key:              1  Last value:                306688
Data records:               306688  Deleted blocks:                 0
Datafile parts:             306688  Deleted data:                   0
Datafile pointer (bytes):        4  Keyfile pointer (bytes):        3
Datafile length:           9347072  Keyfile length:           6066176
Max datafile length:    4294967294  Max keyfile length:   17179868159
Recordlength:                   54
table description:
Key Start Len Index   Type                 Rec/key         Root  Blocksize
1   2     4   unique  long                       1        99328       1024
2   6     20  multip\&. varchar prefix           512      3563520       1024
    27    20          varchar                  512
3   48    3   multip\&. uint24 NULL           306688      6065152       1024
Field Start Length Nullpos Nullbit Type
1     1     1
2     2     4                      no zeros
3     6     21                     varchar
4     27    21                     varchar
5     48    3      1       1       no zeros
6     51    3      1       2       no zeros
.fi
.if n \{\
.RE
.\}
.PP
Explanations for the types of information
\fBmyisamchk\fR
produces are given here\&.
\(lqKeyfile\(rq
refers to the index file\&.
\(lqRecord\(rq
and
\(lqrow\(rq
are synonymous, as are
\(lqfield\(rq
and
\(lqcolumn\&.\(rq
.PP
The initial part of the table description contains these values:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
MyISAM file
.sp
Name of the
MyISAM
(index) file\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Record format
.sp
The format used to store table rows\&. The preceding examples use
Fixed length\&. Other possible values are
Compressed
and
Packed\&. (Packed
corresponds to what
SHOW TABLE STATUS
reports as
Dynamic\&.)
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Chararacter set
.sp
The table default character set\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
File\-version
.sp
Version of
MyISAM
format\&. Currently always 1\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Creation time
.sp
When the data file was created\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Recover time
.sp
When the index/data file was last reconstructed\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Status
.sp
Table status flags\&. Possible values are
crashed,
open,
changed,
analyzed,
optimized keys, and
sorted index pages\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Auto increment key,
Last value
.sp
The key number associated the table\'s
AUTO_INCREMENT
column, and the most recently generated value for this column\&. These fields do not appear if there is no such column\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Data records
.sp
The number of rows in the table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Deleted blocks
.sp
How many deleted blocks still have reserved space\&. You can optimize your table to minimize this space\&. See
Section\ \&6.6.4, \(lqMyISAM Table Optimization\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Datafile parts
.sp
For dynamic\-row format, this indicates how many data blocks there are\&. For an optimized table without fragmented rows, this is the same as
Data records\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Deleted data
.sp
How many bytes of unreclaimed deleted data there are\&. You can optimize your table to minimize this space\&. See
Section\ \&6.6.4, \(lqMyISAM Table Optimization\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Datafile pointer
.sp
The size of the data file pointer, in bytes\&. It is usually 2, 3, 4, or 5 bytes\&. Most tables manage with 2 bytes, but this cannot be controlled from MariaDB yet\&. For fixed tables, this is a row address\&. For dynamic tables, this is a byte address\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Keyfile pointer
.sp
The size of the index file pointer, in bytes\&. It is usually 1, 2, or 3 bytes\&. Most tables manage with 2 bytes, but this is calculated automatically by MariaDB\&. It is always a block address\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Max datafile length
.sp
How long the table data file can become, in bytes\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Max keyfile length
.sp
How long the table index file can become, in bytes\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Recordlength
.sp
How much space each row takes, in bytes\&.
.RE
.PP
The
table description
part of the output includes a list of all keys in the table\&. For each key,
\fBmyisamchk\fR
displays some low\-level information:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Key
.sp
This key\'s number\&. This value is shown only for the first column of the key\&. If this value is missing, the line corresponds to the second or later column of a multiple\-column key\&. For the table shown in the example, there are two
table description
lines for the second index\&. This indicates that it is a multiple\-part index with two parts\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Start
.sp
Where in the row this portion of the index starts\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Len
.sp
How long this portion of the index is\&. For packed numbers, this should always be the full length of the column\&. For strings, it may be shorter than the full length of the indexed column, because you can index a prefix of a string column\&. The total length of a multiple\-part key is the sum of the
Len
values for all key parts\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Index
.sp
Whether a key value can exist multiple times in the index\&. Possible values are
unique
or
multip\&.
(multiple)\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Type
.sp
What data type this portion of the index has\&. This is a
MyISAM
data type with the possible values
packed,
stripped, or
empty\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Root
.sp
Address of the root index block\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Blocksize
.sp
The size of each index block\&. By default this is 1024, but the value may be changed at compile time when MariaDB is built from source\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Rec/key
.sp
This is a statistical value used by the optimizer\&. It tells how many rows there are per value for this index\&. A unique index always has a value of 1\&. This may be updated after a table is loaded (or greatly changed) with
\fBmyisamchk \-a\fR\&. If this is not updated at all, a default value of 30 is given\&.
.RE
.PP
The last part of the output provides information about each column:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Field
.sp
The column number\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Start
.sp
The byte position of the column within table rows\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Length
.sp
The length of the column in bytes\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Nullpos,
Nullbit
.sp
For columns that can be
NULL,
MyISAM
stores
NULL
values as a flag in a byte\&. Depending on how many nullable columns there are, there can be one or more bytes used for this purpose\&. The
Nullpos
and
Nullbit
values, if nonempty, indicate which byte and bit contains that flag indicating whether the column is
NULL\&.
.sp
The position and number of bytes used to store
NULL
flags is shown in the line for field 1\&. This is why there are six
Field
lines for the
person
table even though it has only five columns\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Type
.sp
The data type\&. The value may contain any of the following descriptors:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
constant
.sp
All rows have the same value\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
no endspace
.sp
Do not store endspace\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
no endspace, not_always
.sp
Do not store endspace and do not do endspace compression for all values\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
no endspace, no empty
.sp
Do not store endspace\&. Do not store empty values\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
table\-lookup
.sp
The column was converted to an
ENUM\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
zerofill(\fIN\fR)
.sp
The most significant
\fIN\fR
bytes in the value are always 0 and are not stored\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
no zeros
.sp
Do not store zeros\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
always zero
.sp
Zero values are stored using one bit\&.
.RE
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Huff tree
.sp
The number of the Huffman tree associated with the column\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Bits
.sp
The number of bits used in the Huffman tree\&.
.RE
.PP
The
Huff tree
and
Bits
fields are displayed if the table has been compressed with
\fBmyisampack\fR\&. See
\fBmyisampack\fR(1), for an example of this information\&.
.PP
Example of
\fBmyisamchk \-eiv\fR
output:
.sp
.if n \{\
.RS 4
.\}
.nf
Checking MyISAM file: person
Data records:  306688   Deleted blocks:       0
\- check file\-size
\- check record delete\-chain
No recordlinks
\- check key delete\-chain
block_size 1024:
\- check index reference
\- check data record references index: 1
Key:  1:  Keyblocks used:  98%  Packed:    0%  Max levels:  3
\- check data record references index: 2
Key:  2:  Keyblocks used:  99%  Packed:   97%  Max levels:  3
\- check data record references index: 3
Key:  3:  Keyblocks used:  98%  Packed:  \-14%  Max levels:  3
Total:    Keyblocks used:  98%  Packed:   89%
\- check records and index references
\fI*** LOTS OF ROW NUMBERS DELETED ***\fR
Records:            306688  M\&.recordlength:       25  Packed:            83%
Recordspace used:       97% Empty space:           2% Blocks/Record:   1\&.00
Record blocks:      306688  Delete blocks:         0
Record data:       7934464  Deleted data:          0
Lost space:         256512  Linkdata:        1156096
User time 43\&.08, System time 1\&.68
Maximum resident set size 0, Integral resident set size 0
Non\-physical pagefaults 0, Physical pagefaults 0, Swaps 0
Blocks in 0 out 7, Messages in 0 out 0, Signals 0
Voluntary context switches 0, Involuntary context switches 0
Maximum memory usage: 1046926 bytes (1023k)
.fi
.if n \{\
.RE
.\}
.PP
\fBmyisamchk \-eiv\fR
output includes the following information:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Data records
.sp
The number of rows in the table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Deleted blocks
.sp
How many deleted blocks still have reserved space\&. You can optimize your table to minimize this space\&. See
Section\ \&6.6.4, \(lqMyISAM Table Optimization\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Key
.sp
The key number\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Keyblocks used
.sp
What percentage of the keyblocks are used\&. When a table has just been reorganized with
\fBmyisamchk\fR, the values are very high (very near theoretical maximum)\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Packed
.sp
MariaDB tries to pack key values that have a common suffix\&. This can only be used for indexes on
CHAR
and
VARCHAR
columns\&. For long indexed strings that have similar leftmost parts, this can significantly reduce the space used\&. In the preceding example, the second key is 40 bytes long and a 97% reduction in space is achieved\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Max levels
.sp
How deep the B\-tree for this key is\&. Large tables with long key values get high values\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Records
.sp
How many rows are in the table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
M\&.recordlength
.sp
The average row length\&. This is the exact row length for tables with fixed\-length rows, because all rows have the same length\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Packed
.sp
MariaDB strips spaces from the end of strings\&. The
Packed
value indicates the percentage of savings achieved by doing this\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Recordspace used
.sp
What percentage of the data file is used\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Empty space
.sp
What percentage of the data file is unused\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Blocks/Record
.sp
Average number of blocks per row (that is, how many links a fragmented row is composed of)\&. This is always 1\&.0 for fixed\-format tables\&. This value should stay as close to 1\&.0 as possible\&. If it gets too large, you can reorganize the table\&. See
Section\ \&6.6.4, \(lqMyISAM Table Optimization\(rq\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Recordblocks
.sp
How many blocks (links) are used\&. For fixed\-format tables, this is the same as the number of rows\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Deleteblocks
.sp
How many blocks (links) are deleted\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Recorddata
.sp
How many bytes in the data file are used\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Deleted data
.sp
How many bytes in the data file are deleted (unused)\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Lost space
.sp
If a row is updated to a shorter length, some space is lost\&. This is the sum of all such losses, in bytes\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Linkdata
.sp
When the dynamic table format is used, row fragments are linked with pointers (4 to 7 bytes each)\&.
Linkdata
is the sum of the amount of storage used by all such pointers\&.
.RE
.SH "MYISAMCHK MEMORY USAGE"
.\" memory usage: myisamchk
.PP
Memory allocation is important when you run
\fBmyisamchk\fR\&.
\fBmyisamchk\fR
uses no more memory than its memory\-related variables are set to\&. If you are going to use
\fBmyisamchk\fR
on very large tables, you should first decide how much memory you want it to use\&. The default is to use only about 3MB to perform repairs\&. By using larger values, you can get
\fBmyisamchk\fR
to operate faster\&. For example, if you have more than 32MB RAM, you could use options such as these (in addition to any other options you might specify):
.sp
.if n \{\
.RS 4
.\}
.nf
shell> \fBmyisamchk \-\-sort_buffer_size=16M \e\fR
           \fB\-\-key_buffer_size=16M \e\fR
           \fB\-\-read_buffer_size=1M \e\fR
           \fB\-\-write_buffer_size=1M \&.\&.\&.\fR
.fi
.if n \{\
.RE
.\}
.PP
Using
\fB\-\-sort_buffer_size=16M\fR
should probably be enough for most cases\&.
.PP
Be aware that
\fBmyisamchk\fR
uses temporary files in
TMPDIR\&. If
TMPDIR
points to a memory file system, out of memory errors can easily occur\&. If this happens, run
\fBmyisamchk\fR
with the
\fB\-\-tmpdir=\fR\fB\fIpath\fR\fR
option to specify a directory located on a file system that has more space\&.
.PP
When performing repair operations,
\fBmyisamchk\fR
also needs a lot of disk space:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Twice the size of the data file (the original file and a copy)\&. This space is not needed if you do a repair with
\fB\-\-quick\fR; in this case, only the index file is re\-created\&.
\fIThis space must be available on the same file system as the original data file\fR, as the copy is created in the same directory as the original\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Space for the new index file that replaces the old one\&. The old index file is truncated at the start of the repair operation, so you usually ignore this space\&. This space must be available on the same file system as the original data file\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
When using
\fB\-\-recover\fR
or
\fB\-\-sort\-recover\fR
(but not when using
\fB\-\-safe\-recover\fR), you need space on disk for sorting\&. This space is allocated in the temporary directory (specified by
TMPDIR
or
\fB\-\-tmpdir=\fR\fB\fIpath\fR\fR)\&. The following formula yields the amount of space required:
.sp
.if n \{\
.RS 4
.\}
.nf
(\fIlargest_key\fR + \fIrow_pointer_length\fR) \(mu \fInumber_of_rows\fR \(mu 2
.fi
.if n \{\
.RE
.\}
.sp
You can check the length of the keys and the
\fIrow_pointer_length\fR
with
\fBmyisamchk \-dv \fR\fB\fItbl_name\fR\fR
(see
the section called \(lqMYISAMCHK TABLE INFORMATION\(rq)\&. The
\fIrow_pointer_length\fR
and
\fInumber_of_rows\fR
values are the
Datafile pointer
and
Data records
values in the table description\&. To determine the
\fIlargest_key\fR
value, check the
Key
lines in the table description\&. The
Len
column indicates the number of bytes for each key part\&. For a multiple\-column index, the key size is the sum of the
Len
values for all key parts\&.
.RE
.PP
If you have a problem with disk space during repair, you can try
\fB\-\-safe\-recover\fR
instead of
\fB\-\-recover\fR\&.
.SH "COPYRIGHT"
.br
.PP
Copyright 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc., 2010-2020 MariaDB Foundation
.PP
This documentation is free software; you can redistribute it and/or modify it only under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License.
.PP
This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
.PP
You should have received a copy of the GNU General Public License along with the program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA or see http://www.gnu.org/licenses/.
.sp
.SH "SEE ALSO"
For more information, please refer to the MariaDB Knowledge Base, available online at https://mariadb.com/kb/
.SH AUTHOR
MariaDB Foundation (http://www.mariadb.org/).