myisamchk
(1)
名前
myisamchk - maintenance utility
形式
myisamchk [options] tbl_name ...
説明
MySQL Database System MYISAMCHK(1)
NAME
myisamchk - MyISAM table-maintenance utility
SYNOPSIS
myisamchk [options] tbl_name ...
DESCRIPTION
The myisamchk utility gets information about your database
tables or checks, repairs, or optimizes them. myisamchk
works with MyISAM tables (tables that have .MYD and .MYI
files for storing data and indexes).
You can also use the CHECK TABLE and REPAIR TABLE statements
to check and repair MyISAM tables. See Section 13.7.2.2,
"CHECK TABLE Syntax", and Section 13.7.2.5, "REPAIR TABLE
Syntax".
The use of myisamchk with partitioned tables is not
supported.
Caution
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.
Invoke myisamchk like this:
shell> myisamchk [options] tbl_name ...
The options specify what you want myisamchk to do. They are
described in the following sections. You can also get a list
of options by invoking myisamchk --help.
With no options, myisamchk simply checks your table as the
default operation. To get more information or to tell
myisamchk to take corrective action, specify options as
described in the following discussion.
tbl_name is the database table you want to check or repair.
If you run myisamchk somewhere other than in the database
directory, you must specify the path to the database
directory, because myisamchk has no idea where the database
is located. In fact, myisamchk 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.
You can name several tables on the myisamchk command line if
you wish. You can also specify a table by naming its index
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file (the file with the .MYI suffix). This enables 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:
shell> myisamchk *.MYI
If you are not in the database directory, you can check all
the tables there by specifying the path to the directory:
shell> myisamchk /path/to/database_dir/*.MYI
You can even check all tables in all databases by specifying
a wildcard with the path to the MySQL data directory:
shell> myisamchk /path/to/datadir/*/*.MYI
The recommended way to quickly check all MyISAM tables is:
shell> myisamchk --silent --fast /path/to/datadir/*/*.MYI
If you want to check all MyISAM tables and repair any that
are corrupted, you can use the following command:
shell> myisamchk --silent --force --fast --update-state \
--key_buffer_size=64M --myisam_sort_buffer_size=64M \
--read_buffer_size=1M --write_buffer_size=1M \
/path/to/datadir/*/*.MYI
This command assumes that you have more than 64MB free. For
more information about memory allocation with myisamchk, see
the section called "MYISAMCHK MEMORY USAGE".
For additional information about using myisamchk, see
Section 7.6, "MyISAM Table Maintenance and Crash Recovery".
Important
You must ensure that no other program is using the
tables while you are running myisamchk. The most
effective means of doing so is to shut down the MySQL
server while running myisamchk, or to lock all tables
that myisamchk is being used on.
Otherwise, when you run myisamchk, it may display the
following error message:
warning: clients are using or haven't closed the table properly
This means that you are trying to check a table that has
been updated by another program (such as the mysqld
server) that hasn't yet closed the file or that has died
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without closing the file properly, which can sometimes
lead to the corruption of one or more MyISAM tables.
If mysqld 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 myisamchk
However, the easiest way to avoid this problem is to use
CHECK TABLE instead of myisamchk to check tables. See
Section 13.7.2.2, "CHECK TABLE Syntax".
myisamchk supports the following options, which can be
specified on the command line or in the [myisamchk] group of
an option file. myisamchk also supports the options for
processing option files described at Section 4.2.3.4,
"Command-Line Options that Affect Option-File Handling".
MYISAMCHK GENERAL OPTIONS
The options described in this section can be used for any
type of table maintenance operation performed by myisamchk.
The sections following this one describe options that
pertain only to specific operations, such as table checking
or repairing.
o --help, -?
Display a help message and exit. Options are grouped by
type of operation.
o --HELP, -H
Display a help message and exit. Options are presented
in a single list.
o --debug=debug_options, -# debug_options
Write a debugging log. A typical debug_options string is
'd:t:o,file_name'. The default is
'd:t:o,/tmp/myisamchk.trace'.
o --silent, -s
Silent mode. Write output only when errors occur. You
can use -s twice (-ss) to make myisamchk very silent.
o --verbose, -v
Verbose mode. Print more information about what the
program does. This can be used with -d and -e. Use -v
multiple times (-vv, -vvv) for even more output.
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o --version, -V
Display version information and exit.
o --wait, -w
Instead of terminating with an error if the table is
locked, wait until the table is unlocked before
continuing. If you are running mysqld with external
locking disabled, the table can be locked only by
another myisamchk command.
You can also set the following variables by using
--var_name=value syntax:
+-----------------------+-------------------+
|Variable | Default Value |
+-----------------------+-------------------+
|decode_bits | 9 |
+-----------------------+-------------------+
|ft_max_word_len | version-dependent |
+-----------------------+-------------------+
|ft_min_word_len | 4 |
+-----------------------+-------------------+
|ft_stopword_file | built-in list |
+-----------------------+-------------------+
|key_buffer_size | 523264 |
+-----------------------+-------------------+
|myisam_block_size | 1024 |
+-----------------------+-------------------+
|myisam_sort_key_blocks | 16 |
+-----------------------+-------------------+
|read_buffer_size | 262136 |
+-----------------------+-------------------+
|sort_buffer_size | 2097144 |
+-----------------------+-------------------+
|sort_key_blocks | 16 |
+-----------------------+-------------------+
|stats_method | nulls_unequal |
+-----------------------+-------------------+
|write_buffer_size | 262136 |
+-----------------------+-------------------+
The possible myisamchk variables and their default values
can be examined with myisamchk --help:
sort_buffer_size is used when the keys are repaired by
sorting keys, which is the normal case when you use
--recover. As of MySQL 5.5.29, myisam_sort_buffer_size is
available as an alternative name to sort_buffer_size.
myisam_sort_buffer_size is preferable to sort_buffer_size
because its name corresponds to the myisam_sort_buffer_size
server system variable that has a similar meaning.
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sort_buffer_size should be considered deprecated.
key_buffer_size is used when you are checking the table with
--extend-check 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:
o You use --safe-recover.
o 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 myisamchk to repair by sorting, you can use
the --sort-recover option.
Repairing through the key buffer takes much less disk space
than using sorting, but is also much slower.
If you want a faster repair, set the key_buffer_size and
myisam_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.
myisam_block_size is the size used for index blocks.
stats_method influences how NULL values are treated for
index statistics collection when the --analyze 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, "Server System
Variables", and Section 8.3.7, "InnoDB and MyISAM Index
Statistics Collection".
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.
If you use myisamchk 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.
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
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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 myisamchk that you use for
mysqld. For example, if you have set the minimum word length
to 3, you can repair a table with myisamchk like this:
shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI
To ensure that myisamchk 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:
[mysqld]
ft_min_word_len=3
[myisamchk]
ft_min_word_len=3
An alternative to using myisamchk 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.
MYISAMCHK CHECK OPTIONS
myisamchk supports the following options for table checking
operations:
o --check, -c
Check the table for errors. This is the default
operation if you specify no option that selects an
operation type explicitly.
o --check-only-changed, -C
Check only tables that have changed since the last
check.
o --extend-check, -e
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, myisamchk or myisamchk
--medium-check should be able to determine whether there
are any errors in the table.
If you are using --extend-check and have plenty of
memory, setting the key_buffer_size variable to a large
value helps the repair operation run faster.
See also the description of this option under table
repair options.
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For a description of the output format, see the section
called "OBTAINING TABLE INFORMATION WITH MYISAMCHK".
o --fast, -F
Check only tables that haven't been closed properly.
o --force, -f
Do a repair operation automatically if myisamchk finds
any errors in the table. The repair type is the same as
that specified with the --recover or -r option.
o --information, -i
Print informational statistics about the table that is
checked.
o --medium-check, -m
Do a check that is faster than an --extend-check
operation. This finds only 99.99% of all errors, which
should be good enough in most cases.
o --read-only, -T
Do not mark the table as checked. This is useful if you
use myisamchk to check a table that is in use by some
other application that does not use locking, such as
mysqld when run with external locking disabled.
o --update-state, -U
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
--check-only-changed option, but you shouldn't use this
option if the mysqld server is using the table and you
are running it with external locking disabled.
MYISAMCHK REPAIR OPTIONS
myisamchk supports the following options for table repair
operations (operations performed when an option such as
--recover or --safe-recover is given):
o --backup, -B
Make a backup of the .MYD file as file_name-time.BAK
o --character-sets-dir=path
The directory where character sets are installed. See
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Section 10.5, "Character Set Configuration".
o --correct-checksum
Correct the checksum information for the table.
o --data-file-length=len, -D len
The maximum length of the data file (when re-creating
data file when it is "full").
o --extend-check, -e
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.
See also the description of this option under table
checking options.
For a description of the output format, see the section
called "OBTAINING TABLE INFORMATION WITH MYISAMCHK".
o --force, -f
Overwrite old intermediate files (files with names like
tbl_name.TMD) instead of aborting.
o --keys-used=val, -k val
For myisamchk, 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
myisamchk -r.
o --no-symlinks, -l
Do not follow symbolic links. Normally myisamchk repairs
the table that a symlink points to. This option does not
exist as of MySQL 4.0 because versions from 4.0 on do
not remove symlinks during repair operations.
o --max-record-length=len
Skip rows larger than the given length if myisamchk
cannot allocate memory to hold them.
o --parallel-recover, -p
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Use the same technique as -r and -n, but create all the
keys in parallel, using different threads. This is
beta-quality code. Use at your own risk!
o --quick, -q
Achieve a faster repair by modifying only the index
file, not the data file. You can specify this option
twice to force myisamchk to modify the original data
file in case of duplicate keys.
o --recover, -r
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 --safe-recover only if myisamchk reports that
the table cannot be recovered using --recover. (In the
unlikely case that --recover fails, the data file
remains intact.)
If you have lots of memory, you should increase the
value of myisam_sort_buffer_size.
o --safe-recover, -o
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 --recover, but can handle a couple of very
unlikely cases that --recover cannot. This recovery
method also uses much less disk space than --recover.
Normally, you should repair first using --recover, and
then with --safe-recover only if --recover fails.
If you have lots of memory, you should increase the
value of key_buffer_size.
o --set-character-set=name
Change the character set used by the table indexes. This
option was replaced by --set-collation in MySQL 5.0.3.
o --set-collation=name
Specify the collation to use for sorting table indexes.
The character set name is implied by the first part of
the collation name.
o --sort-recover, -n
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Force myisamchk to use sorting to resolve the keys even
if the temporary files would be very large.
o --tmpdir=path, -t path
The path of the directory to be used for storing
temporary files. If this is not set, myisamchk 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 (":") on Unix and the
semicolon (";") on Windows.
o --unpack, -u
Unpack a table that was packed with myisampack.
OTHER MYISAMCHK OPTIONS
myisamchk supports the following options for actions other
than table checks and repairs:
o --analyze, -a
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 myisamchk --description
--verbose tbl_name command or the SHOW INDEX FROM
tbl_name statement.
o --block-search=offset, -b offset
Find the record that a block at the given offset belongs
to.
o --description, -d
Print some descriptive information about the table.
Specifying the --verbose option once or twice produces
additional information. See the section called
"OBTAINING TABLE INFORMATION WITH MYISAMCHK".
o --set-auto-increment[=value], -A[value]
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 value
is not specified, AUTO_INCREMENT numbers for new records
begin with the largest value currently in the table,
plus one.
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o --sort-index, -S
Sort the index tree blocks in high-low order. This
optimizes seeks and makes table scans that use indexes
faster.
o --sort-records=N, -R N
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 myisamchk sees them.
Indexes are numbered beginning with 1.
If keys are not packed (PACK_KEYS=0), they have the same
length, so when myisamchk sorts and moves records, it
just overwrites record offsets in the index. If keys are
packed (PACK_KEYS=1), myisamchk 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.)
OBTAINING TABLE INFORMATION WITH MYISAMCHK
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.
o myisamchk -d tbl_name
Runs myisamchk in "describe mode" to produce a
description of your table. If you start the MySQL server
with external locking disabled, myisamchk may report an
error for a table that is updated while it runs.
However, because myisamchk does not change the table in
describe mode, there is no risk of destroying data.
o myisamchk -dv tbl_name
Adding -v runs myisamchk in verbose mode so that it
produces more information about the table. Adding -v a
second time produces even more information.
o myisamchk -eis tbl_name
Shows only the most important information from a table.
This operation is slow because it must read the entire
table.
o myisamchk -eiv tbl_name
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This is like -eis, but tells you what is being done.
The tbl_name argument can be either the name of a MyISAM
table or the name of its index file, as described in
myisamchk(1). Multiple tbl_name arguments can be given.
Suppose that a table named person has the following
structure. (The MAX_ROWS table option is included so that in
the example output from myisamchk shown later, some values
are smaller and fit the output format more easily.)
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;
Suppose also that the table has these data and index file
sizes:
-rw-rw---- 1 mysql mysql 9347072 Aug 19 11:47 person.MYD
-rw-rw---- 1 mysql mysql 6066176 Aug 19 11:47 person.MYI
Example of myisamchk -dvv output:
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
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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
Explanations for the types of information myisamchk produces
are given here. "Keyfile" refers to the index file.
"Record" and "row" are synonymous, as are "field" and
"column."
The initial part of the table description contains these
values:
o MyISAM file
Name of the MyISAM (index) file.
o Record format
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.)
o Chararacter set
The table default character set.
o File-version
Version of MyISAM format. Currently always 1.
o Creation time
When the data file was created.
o Recover time
When the index/data file was last reconstructed.
o Status
Table status flags. Possible values are crashed, open,
changed, analyzed, optimized keys, and sorted index
pages.
o Auto increment key, Last value
The key number associated the table's AUTO_INCREMENT
column, and the most recently generated value for this
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column. These fields do not appear if there is no such
column.
o Data records
The number of rows in the table.
o Deleted blocks
How many deleted blocks still have reserved space. You
can optimize your table to minimize this space. See
Section 7.6.4, "MyISAM Table Optimization".
o Datafile parts
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.
o Deleted data
How many bytes of unreclaimed deleted data there are.
You can optimize your table to minimize this space. See
Section 7.6.4, "MyISAM Table Optimization".
o Datafile pointer
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 MySQL yet. For
fixed tables, this is a row address. For dynamic tables,
this is a byte address.
o Keyfile pointer
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 MySQL. It
is always a block address.
o Max datafile length
How long the table data file can become, in bytes.
o Max keyfile length
How long the table index file can become, in bytes.
o Recordlength
How much space each row takes, in bytes.
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The table description part of the output includes a list of
all keys in the table. For each key, myisamchk displays some
low-level information:
o Key
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.
o Start
Where in the row this portion of the index starts.
o Len
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.
o Index
Whether a key value can exist multiple times in the
index. Possible values are unique or multip.
(multiple).
o Type
What data type this portion of the index has. This is a
MyISAM data type with the possible values packed,
stripped, or empty.
o Root
Address of the root index block.
o Blocksize
The size of each index block. By default this is 1024,
but the value may be changed at compile time when MySQL
is built from source.
o Rec/key
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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 myisamchk -a. If this is not updated at all, a
default value of 30 is given.
The last part of the output provides information about each
column:
o Field
The column number.
o Start
The byte position of the column within table rows.
o Length
The length of the column in bytes.
o Nullpos, Nullbit
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.
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.
o Type
The data type. The value may contain any of the
following descriptors:
o constant
All rows have the same value.
o no endspace
Do not store endspace.
o no endspace, not_always
Do not store endspace and do not do endspace
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compression for all values.
o no endspace, no empty
Do not store endspace. Do not store empty values.
o table-lookup
The column was converted to an ENUM.
o zerofill(N)
The most significant N bytes in the value are always
0 and are not stored.
o no zeros
Do not store zeros.
o always zero
Zero values are stored using one bit.
o Huff tree
The number of the Huffman tree associated with the
column.
o Bits
The number of bits used in the Huffman tree.
The Huff tree and Bits fields are displayed if the table has
been compressed with myisampack. See myisampack(1), for an
example of this information.
Example of myisamchk -eiv output:
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
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Total: Keyblocks used: 98% Packed: 89%
- check records and index references*** LOTS OF ROW NUMBERS DELETED ***
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)
myisamchk -eiv output includes the following information:
o Data records
The number of rows in the table.
o Deleted blocks
How many deleted blocks still have reserved space. You
can optimize your table to minimize this space. See
Section 7.6.4, "MyISAM Table Optimization".
o Key
The key number.
o Keyblocks used
What percentage of the keyblocks are used. When a table
has just been reorganized with myisamchk, the values are
very high (very near theoretical maximum).
o Packed
MySQL 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.
o Max levels
How deep the B-tree for this key is. Large tables with
long key values get high values.
o Records
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How many rows are in the table.
o M.recordlength
The average row length. This is the exact row length for
tables with fixed-length rows, because all rows have the
same length.
o Packed
MySQL strips spaces from the end of strings. The Packed
value indicates the percentage of savings achieved by
doing this.
o Recordspace used
What percentage of the data file is used.
o Empty space
What percentage of the data file is unused.
o Blocks/Record
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 7.6.4, "MyISAM Table
Optimization".
o Recordblocks
How many blocks (links) are used. For fixed-format
tables, this is the same as the number of rows.
o Deleteblocks
How many blocks (links) are deleted.
o Recorddata
How many bytes in the data file are used.
o Deleted data
How many bytes in the data file are deleted (unused).
o Lost space
If a row is updated to a shorter length, some space is
lost. This is the sum of all such losses, in bytes.
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o Linkdata
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.
MYISAMCHK MEMORY USAGE
Memory allocation is important when you run myisamchk.
myisamchk uses no more memory than its memory-related
variables are set to. If you are going to use myisamchk 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
myisamchk to operate faster. For example, if you have more
than 512MB RAM available, you could use options such as
these (in addition to any other options you might specify):
shell> myisamchk --myisam_sort_buffer_size=256M \
--key_buffer_size=512M \
--read_buffer_size=64M \
--write_buffer_size=64M ...
Using --myisam_sort_buffer_size=16M is probably enough for
most cases.
Be aware that myisamchk uses temporary files in TMPDIR. If
TMPDIR points to a memory file system, out of memory errors
can easily occur. If this happens, run myisamchk with the
--tmpdir=path option to specify a directory located on a
file system that has more space.
When performing repair operations, myisamchk also needs a
lot of disk space:
o Twice the size of the data file (the original file and a
copy). This space is not needed if you do a repair with
--quick; in this case, only the index file is
re-created. This space must be available on the same
file system as the original data file, as the copy is
created in the same directory as the original.
o 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.
o When using --recover or --sort-recover (but not when
using --safe-recover), you need space on disk for
sorting. This space is allocated in the temporary
directory (specified by TMPDIR or --tmpdir=path). The
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following formula yields the amount of space required:
(largest_key + row_pointer_length) * number_of_rows * 2
You can check the length of the keys and the
row_pointer_length with myisamchk -dv tbl_name (see the
section called "OBTAINING TABLE INFORMATION WITH
MYISAMCHK"). The row_pointer_length and number_of_rows
values are the Datafile pointer and Data records values
in the table description. To determine the largest_key
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.
If you have a problem with disk space during repair, you can
try --safe-recover instead of --recover.
COPYRIGHT
Copyright (C) 1997, 2013, Oracle and/or its affiliates. All
rights reserved.
This software and related documentation are provided under a
license agreement containing restrictions on use and
disclosure and are protected by intellectual property laws.
Except as expressly permitted in your license agreement or
allowed by law, you may not use, copy, reproduce, translate,
broadcast, modify, license, transmit, distribute, exhibit,
perform, publish, or display any part, in any form, or by
any means. Reverse engineering, disassembly, or
decompilation of this software, unless required by law for
interoperability, is prohibited.
The information contained herein is subject to change
without notice and is not warranted to be error-free. If you
find any errors, please report them to us in writing.
If this software or related documentation is delivered to
the U.S. Government or anyone licensing it on behalf of the
U.S. Government, the following notice is applicable:
U.S. GOVERNMENT RIGHTS Programs, software, databases, and
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Government customers are "commercial computer software" or
"commercial technical data" pursuant to the applicable
Federal Acquisition Regulation and agency-specific
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the restrictions and license terms set forth in the
applicable Government contract, and, to the extent
applicable by the terms of the Government contract, the
additional rights set forth in FAR 52.227-19, Commercial
MySQL 5.5 Last change: 03/22/2013 21
MySQL Database System MYISAMCHK(1)
Computer Software License (December 2007). Oracle USA, Inc.,
500 Oracle Parkway, Redwood City, CA 94065.
This software is developed for general use in a variety of
information management applications. It is not developed or
intended for use in any inherently dangerous applications,
including applications which may create a risk of personal
injury. If you use this software in dangerous applications,
then you shall be responsible to take all appropriate fail-
safe, backup, redundancy, and other measures to ensure the
safe use of this software. Oracle Corporation and its
affiliates disclaim any liability for any damages caused by
use of this software in dangerous applications.
Oracle is a registered trademark of Oracle Corporation
and/or its affiliates. MySQL is a trademark of Oracle
Corporation and/or its affiliates, and shall not be used
without Oracle's express written authorization. Other names
may be trademarks of their respective owners.
This software and documentation may provide access to or
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responsible for and expressly disclaim all warranties of any
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your access to or use of third-party content, products, or
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is subject to the terms and conditions of your Oracle
Software License and Service Agreement, which has been
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and information contained herein may not be disclosed,
copied, reproduced, or distributed to anyone outside Oracle
without prior written consent of Oracle or as specifically
provided below. This document is not part of your license
agreement nor can it be incorporated into any contractual
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This documentation is NOT distributed under a GPL license.
Use of this documentation is subject to the following terms:
You may create a printed copy of this documentation solely
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edited in any way. You shall not publish or distribute this
documentation in any form or on any media, except if you
distribute the documentation in a manner similar to how
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MySQL Database System MYISAMCHK(1)
Oracle disseminates it (that is, electronically for download
on a Web site with the software) or on a CD-ROM or similar
medium, provided however that the documentation is
disseminated together with the software on the same medium.
Any other use, such as any dissemination of printed copies
or use of this documentation, in whole or in part, in
another publication, requires the prior written consent from
an authorized representative of Oracle. Oracle and/or its
affiliates reserve any and all rights to this documentation
not expressly granted above.
For more information on the terms of this license, or for
details on how the MySQL documentation is built and
produced, please visit blue]MySQL Contact & Questions].
For additional licensing information, including licenses for
third-party libraries used by MySQL products, see Preface
and Legal Notices.
For help with using MySQL, please visit either the
blue]MySQL Forums] or blue]MySQL Mailing Lists] where you
can discuss your issues with other MySQL users.
For additional documentation on MySQL products, including
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ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+-------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-------------------+
|Availability | database/mysql-55 |
+---------------+-------------------+
|Stability | Uncommitted |
+---------------+-------------------+
SEE ALSO
For more information, please refer to the MySQL Reference
Manual, which may already be installed locally and which is
also available online at http://dev.mysql.com/doc/.
AUTHOR
Oracle Corporation (http://dev.mysql.com/).
MySQL 5.5 Last change: 03/22/2013 23
MySQL Database System MYISAMCHK(1)
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://downloads.mysql.com/archives/mysql-5.5/mysql-5.5.31.tar.gz
Further information about this software can be found on the
open source community website at http://dev.mysql.com/.
MySQL 5.5 Last change: 03/22/2013 24