1MYISAMCHK(1) MySQL Database System MYISAMCHK(1)
2
6 myisamchk - MyISAM table-maintenance utility
7
9 myisamchk [options] tbl_name ...
10
12 The myisamchk utility gets information about your database tables or
13 checks, repairs, or optimizes them. myisamchk works with MyISAM tables
14 (tables that have .MYD and .MYI files for storing data and indexes).
15 You can also use the CHECK TABLE and REPAIR TABLE statements to check
17 and repair MyISAM tables. See Section 13.7.2.3, “CHECK TABLE Syntax”,
18 and Section 13.7.2.6, “REPAIR TABLE Syntax”.
19 The use of myisamchk with partitioned tables is not supported.
21 Caution
23 It is best to make a backup of a table before performing a table
24 repair operation; under some circumstances the operation might
25 cause data loss. Possible causes include but are not limited to
26 file system errors.
27 Invoke myisamchk like this:
29 shell> myisamchk [options] tbl_name ...
31 The options specify what you want myisamchk to do. They are described
33 in the following sections. You can also get a list of options by
34 invoking myisamchk --help.
35 With no options, myisamchk simply checks your table as the default
37 operation. To get more information or to tell myisamchk to take
38 corrective action, specify options as described in the following
39 discussion.
40 tbl_name is the database table you want to check or repair. If you run
42 myisamchk somewhere other than in the database directory, you must
43 specify the path to the database directory, because myisamchk has no
44 idea where the database is located. In fact, myisamchk does not
45 actually care whether the files you are working on are located in a
46 database directory. You can copy the files that correspond to a
47 database table into some other location and perform recovery operations
48 on them there.
49 You can name several tables on the myisamchk command line if you wish.
51 You can also specify a table by naming its index file (the file with
52 the .MYI suffix). This enables you to specify all tables in a directory
53 by using the pattern *.MYI. For example, if you are in a database
54 directory, you can check all the MyISAM tables in that directory like
55 this:
56 shell> myisamchk *.MYI
58 If you are not in the database directory, you can check all the tables
60 there by specifying the path to the directory:
61 shell> myisamchk /path/to/database_dir/*.MYI
63 You can even check all tables in all databases by specifying a wildcard
65 with the path to the MySQL data directory:
66 shell> myisamchk /path/to/datadir/*/*.MYI
68 The recommended way to quickly check all MyISAM tables is:
70 shell> myisamchk --silent --fast /path/to/datadir/*/*.MYI
72 If you want to check all MyISAM tables and repair any that are
74 corrupted, you can use the following command:
75 shell> myisamchk --silent --force --fast --update-state \
77 --key_buffer_size=64M --myisam_sort_buffer_size=64M \
78 --read_buffer_size=1M --write_buffer_size=1M \
79 /path/to/datadir/*/*.MYI
80 This command assumes that you have more than 64MB free. For more
82 information about memory allocation with myisamchk, see the section
83 called “MYISAMCHK MEMORY USAGE”.
84 For additional information about using myisamchk, see Section 7.6,
86 “MyISAM Table Maintenance and Crash Recovery”.
87 Important
89 You must ensure that no other program is using the tables while you
90 are running myisamchk. The most effective means of doing so is to
91 shut down the MySQL server while running myisamchk, or to lock all
92 tables that myisamchk is being used on.
93 Otherwise, when you run myisamchk, it may display the following
95 error message:
96 warning: clients are using or haven't closed the table properly
98 This means that you are trying to check a table that has been
100 updated by another program (such as the mysqld server) that hasn't
101 yet closed the file or that has died without closing the file
102 properly, which can sometimes lead to the corruption of one or more
103 MyISAM tables.
104 If mysqld is running, you must force it to flush any table
106 modifications that are still buffered in memory by using FLUSH
107 TABLES. You should then ensure that no one is using the tables
108 while you are running myisamchk
109 However, the easiest way to avoid this problem is to use CHECK
111 TABLE instead of myisamchk to check tables. See Section 13.7.2.3,
112 “CHECK TABLE Syntax”.
113 myisamchk supports the following options, which can be specified on the
115 command line or in the [myisamchk] group of an option file. myisamchk
116 also supports the options for processing option files described at
117 Section 4.2.3.4, “Command-Line Options that Affect Option-File
118 Handling”.
119
121 The options described in this section can be used for any type of table
122 maintenance operation performed by myisamchk. The sections following
123 this one describe options that pertain only to specific operations,
124 such as table checking or repairing.
125 · --help, -?
127 Display a help message and exit. Options are grouped by type of
129 operation.
130 · --HELP, -H
132 Display a help message and exit. Options are presented in a single
134 list.
135 · --debug=debug_options, -# debug_options
137 Write a debugging log. A typical debug_options string is
139 'd:t:o,file_name'. The default is 'd:t:o,/tmp/myisamchk.trace'.
140 · --silent, -s
142 Silent mode. Write output only when errors occur. You can use -s
144 twice (-ss) to make myisamchk very silent.
145 · --verbose, -v
147 Verbose mode. Print more information about what the program does.
149 This can be used with -d and -e. Use -v multiple times (-vv, -vvv)
150 for even more output.
151 · --version, -V
153 Display version information and exit.
155 · --wait, -w
157 Instead of terminating with an error if the table is locked, wait
159 until the table is unlocked before continuing. If you are running
160 mysqld with external locking disabled, the table can be locked only
161 by another myisamchk command.
162 You can also set the following variables by using --var_name=value
164 syntax:
165 ┌───────────────────────┬───────────────────┐
167 │Variable │ Default Value │
168 ├───────────────────────┼───────────────────┤
169 │decode_bits │ 9 │
170 ├───────────────────────┼───────────────────┤
171 │ft_max_word_len │ version-dependent │
172 ├───────────────────────┼───────────────────┤
173 │ft_min_word_len │ 4 │
174 ├───────────────────────┼───────────────────┤
175 │ft_stopword_file │ built-in list │
176 ├───────────────────────┼───────────────────┤
177 │key_buffer_size │ 523264 │
178 ├───────────────────────┼───────────────────┤
179 │myisam_block_size │ 1024 │
180 ├───────────────────────┼───────────────────┤
181 │myisam_sort_key_blocks │ 16 │
182 ├───────────────────────┼───────────────────┤
183 │read_buffer_size │ 262136 │
184 ├───────────────────────┼───────────────────┤
185 │sort_buffer_size │ 2097144 │
186 ├───────────────────────┼───────────────────┤
187 │sort_key_blocks │ 16 │
188 ├───────────────────────┼───────────────────┤
189 │stats_method │ nulls_unequal │
190 ├───────────────────────┼───────────────────┤
191 │write_buffer_size │ 262136 │
192 └───────────────────────┴───────────────────┘
193 The possible myisamchk variables and their default values can be
195 examined with myisamchk --help:
196 sort_buffer_size is used when the keys are repaired by sorting keys,
198 which is the normal case when you use --recover. As of MySQL 5.1.67,
199 myisam_sort_buffer_size is available as an alternative name to
200 sort_buffer_size. myisam_sort_buffer_size is preferable to
201 sort_buffer_size because its name corresponds to the
202 myisam_sort_buffer_size server system variable that has a similar
203 meaning. sort_buffer_size should be considered deprecated.
204 key_buffer_size is used when you are checking the table with
206 --extend-check or when the keys are repaired by inserting keys row by
207 row into the table (like when doing normal inserts). Repairing through
208 the key buffer is used in the following cases:
209 · You use --safe-recover.
211 · The temporary files needed to sort the keys would be more than
213 twice as big as when creating the key file directly. This is often
214 the case when you have large key values for CHAR, VARCHAR, or TEXT
215 columns, because the sort operation needs to store the complete key
216 values as it proceeds. If you have lots of temporary space and you
217 can force myisamchk to repair by sorting, you can use the
218 --sort-recover option.
219 Repairing through the key buffer takes much less disk space than using
221 sorting, but is also much slower.
222 If you want a faster repair, set the key_buffer_size and
224 myisam_sort_buffer_size variables to about 25% of your available
225 memory. You can set both variables to large values, because only one of
226 them is used at a time.
227 myisam_block_size is the size used for index blocks.
229 stats_method influences how NULL values are treated for index
231 statistics collection when the --analyze option is given. It acts like
232 the myisam_stats_method system variable. For more information, see the
233 description of myisam_stats_method in Section 5.1.4, “Server System
234 Variables”, and Section 8.5.4, “InnoDB and MyISAM Index Statistics
235 Collection”.
236 ft_min_word_len and ft_max_word_len indicate the minimum and maximum
238 word length for FULLTEXT indexes. ft_stopword_file names the stopword
239 file. These need to be set under the following circumstances.
240 If you use myisamchk to perform an operation that modifies table
242 indexes (such as repair or analyze), the FULLTEXT indexes are rebuilt
243 using the default full-text parameter values for minimum and maximum
244 word length and the stopword file unless you specify otherwise. This
245 can result in queries failing.
246 The problem occurs because these parameters are known only by the
248 server. They are not stored in MyISAM index files. To avoid the problem
249 if you have modified the minimum or maximum word length or the stopword
250 file in the server, specify the same ft_min_word_len, ft_max_word_len,
251 and ft_stopword_file values to myisamchk that you use for mysqld. For
252 example, if you have set the minimum word length to 3, you can repair a
253 table with myisamchk like this:
254 shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI
256 To ensure that myisamchk and the server use the same values for
258 full-text parameters, you can place each one in both the [mysqld] and
259 [myisamchk] sections of an option file:
260 [mysqld]
262 ft_min_word_len=3
263 [myisamchk]
264 ft_min_word_len=3
265 An alternative to using myisamchk is to use the REPAIR TABLE, ANALYZE
267 TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements are performed
268 by the server, which knows the proper full-text parameter values to
269 use.
270
272 myisamchk supports the following options for table checking operations:
273 · --check, -c
275 Check the table for errors. This is the default operation if you
277 specify no option that selects an operation type explicitly.
278 · --check-only-changed, -C
280 Check only tables that have changed since the last check.
282 · --extend-check, -e
284 Check the table very thoroughly. This is quite slow if the table
286 has many indexes. This option should only be used in extreme cases.
287 Normally, myisamchk or myisamchk --medium-check should be able to
288 determine whether there are any errors in the table.
289 If you are using --extend-check and have plenty of memory, setting
291 the key_buffer_size variable to a large value helps the repair
292 operation run faster.
293 See also the description of this option under table repair options.
295 For a description of the output format, see the section called
297 “OBTAINING TABLE INFORMATION WITH MYISAMCHK”.
298 · --fast, -F
300 Check only tables that haven't been closed properly.
302 · --force, -f
304 Do a repair operation automatically if myisamchk finds any errors
306 in the table. The repair type is the same as that specified with
307 the --recover or -r option.
308 · --information, -i
310 Print informational statistics about the table that is checked.
312 · --medium-check, -m
314 Do a check that is faster than an --extend-check operation. This
316 finds only 99.99% of all errors, which should be good enough in
317 most cases.
318 · --read-only, -T
320 Do not mark the table as checked. This is useful if you use
322 myisamchk to check a table that is in use by some other application
323 that does not use locking, such as mysqld when run with external
324 locking disabled.
325 · --update-state, -U
327 Store information in the .MYI file to indicate when the table was
329 checked and whether the table crashed. This should be used to get
330 full benefit of the --check-only-changed option, but you shouldn't
331 use this option if the mysqld server is using the table and you are
332 running it with external locking disabled.
333
335 myisamchk supports the following options for table repair operations
336 (operations performed when an option such as --recover or
337 --safe-recover is given):
338 · --backup, -B
340 Make a backup of the .MYD file as file_name-time.BAK
342 · --character-sets-dir=path
344 The directory where character sets are installed. See Section 10.5,
346 “Character Set Configuration”.
347 · --correct-checksum
349 Correct the checksum information for the table.
351 · --data-file-length=len, -D len
353 The maximum length of the data file (when re-creating data file
355 when it is “full”).
356 · --extend-check, -e
358 Do a repair that tries to recover every possible row from the data
360 file. Normally, this also finds a lot of garbage rows. Do not use
361 this option unless you are desperate.
362 See also the description of this option under table checking
364 options.
365 For a description of the output format, see the section called
367 “OBTAINING TABLE INFORMATION WITH MYISAMCHK”.
368 · --force, -f
370 Overwrite old intermediate files (files with names like
372 tbl_name.TMD) instead of aborting.
373 · --keys-used=val, -k val
375 For myisamchk, the option value is a bit-value that indicates which
377 indexes to update. Each binary bit of the option value corresponds
378 to a table index, where the first index is bit 0. An option value
379 of 0 disables updates to all indexes, which can be used to get
380 faster inserts. Deactivated indexes can be reactivated by using
381 myisamchk -r.
382 · --no-symlinks, -l
384 Do not follow symbolic links. Normally myisamchk repairs the table
386 that a symlink points to. This option does not exist as of MySQL
387 4.0 because versions from 4.0 on do not remove symlinks during
388 repair operations.
389 · --max-record-length=len
391 Skip rows larger than the given length if myisamchk cannot allocate
393 memory to hold them.
394 · --parallel-recover, -p
396 Use the same technique as -r and -n, but create all the keys in
398 parallel, using different threads. This is beta-quality code. Use
399 at your own risk!
400 · --quick, -q
402 Achieve a faster repair by modifying only the index file, not the
404 data file. You can specify this option twice to force myisamchk to
405 modify the original data file in case of duplicate keys.
406 · --recover, -r
408 Do a repair that can fix almost any problem except unique keys that
410 are not unique (which is an extremely unlikely error with MyISAM
411 tables). If you want to recover a table, this is the option to try
412 first. You should try --safe-recover only if myisamchk reports that
413 the table cannot be recovered using --recover. (In the unlikely
414 case that --recover fails, the data file remains intact.)
415 If you have lots of memory, you should increase the value of
417 myisam_sort_buffer_size.
418 · --safe-recover, -o
420 Do a repair using an old recovery method that reads through all
422 rows in order and updates all index trees based on the rows found.
423 This is an order of magnitude slower than --recover, but can handle
424 a couple of very unlikely cases that --recover cannot. This
425 recovery method also uses much less disk space than --recover.
426 Normally, you should repair first using --recover, and then with
427 --safe-recover only if --recover fails.
428 If you have lots of memory, you should increase the value of
430 key_buffer_size.
431 · --set-character-set=name
433 Change the character set used by the table indexes. This option was
435 replaced by --set-collation in MySQL 5.0.3.
436 · --set-collation=name
438 Specify the collation to use for sorting table indexes. The
440 character set name is implied by the first part of the collation
441 name.
442 · --sort-recover, -n
444 Force myisamchk to use sorting to resolve the keys even if the
446 temporary files would be very large.
447 · --tmpdir=path, -t path
449 The path of the directory to be used for storing temporary files.
451 If this is not set, myisamchk uses the value of the TMPDIR
452 environment variable. --tmpdir can be set to a list of directory
453 paths that are used successively in round-robin fashion for
454 creating temporary files. The separator character between directory
455 names is the colon (“:”) on Unix and the semicolon (“;”) on
456 Windows, NetWare, and OS/2.
457 · --unpack, -u
459 Unpack a table that was packed with myisampack.
461
463 myisamchk supports the following options for actions other than table
464 checks and repairs:
465 · --analyze, -a
467 Analyze the distribution of key values. This improves join
469 performance by enabling the join optimizer to better choose the
470 order in which to join the tables and which indexes it should use.
471 To obtain information about the key distribution, use a myisamchk
472 --description --verbose tbl_name command or the SHOW INDEX FROM
473 tbl_name statement.
474 · --block-search=offset, -b offset
476 Find the record that a block at the given offset belongs to.
478 · --description, -d
480 Print some descriptive information about the table. Specifying the
482 --verbose option once or twice produces additional information. See
483 the section called “OBTAINING TABLE INFORMATION WITH MYISAMCHK”.
484 · --set-auto-increment[=value], -A[value]
486 Force AUTO_INCREMENT numbering for new records to start at the
488 given value (or higher, if there are existing records with
489 AUTO_INCREMENT values this large). If value is not specified,
490 AUTO_INCREMENT numbers for new records begin with the largest value
491 currently in the table, plus one.
492 · --sort-index, -S
494 Sort the index tree blocks in high-low order. This optimizes seeks
496 and makes table scans that use indexes faster.
497 · --sort-records=N, -R N
499 Sort records according to a particular index. This makes your data
501 much more localized and may speed up range-based SELECT and ORDER
502 BY operations that use this index. (The first time you use this
503 option to sort a table, it may be very slow.) To determine a
504 table's index numbers, use SHOW INDEX, which displays a table's
505 indexes in the same order that myisamchk sees them. Indexes are
506 numbered beginning with 1.
507 If keys are not packed (PACK_KEYS=0), they have the same length, so
509 when myisamchk sorts and moves records, it just overwrites record
510 offsets in the index. If keys are packed (PACK_KEYS=1), myisamchk
511 must unpack key blocks first, then re-create indexes and pack the
512 key blocks again. (In this case, re-creating indexes is faster than
513 updating offsets for each index.)
514
516 To obtain a description of a MyISAM table or statistics about it, use
517 the commands shown here. The output from these commands is explained
518 later in this section.
519 · myisamchk -d tbl_name
521 Runs myisamchk in “describe mode” to produce a description of your
523 table. If you start the MySQL server with external locking
524 disabled, myisamchk may report an error for a table that is updated
525 while it runs. However, because myisamchk does not change the table
526 in describe mode, there is no risk of destroying data.
527 · myisamchk -dv tbl_name
529 Adding -v runs myisamchk in verbose mode so that it produces more
531 information about the table. Adding -v a second time produces even
532 more information.
533 · myisamchk -eis tbl_name
535 Shows only the most important information from a table. This
537 operation is slow because it must read the entire table.
538 · myisamchk -eiv tbl_name
540 This is like -eis, but tells you what is being done.
542 The tbl_name argument can be either the name of a MyISAM table or the
544 name of its index file, as described in myisamchk(1). Multiple tbl_name
545 arguments can be given.
546 Suppose that a table named person has the following structure. (The
548 MAX_ROWS table option is included so that in the example output from
549 myisamchk shown later, some values are smaller and fit the output
550 format more easily.)
551 CREATE TABLE person
553 (
554 id INT NOT NULL AUTO_INCREMENT,
555 last_name VARCHAR(20) NOT NULL,
556 first_name VARCHAR(20) NOT NULL,
557 birth DATE,
558 death DATE,
559 PRIMARY KEY (id),
560 INDEX (last_name, first_name),
561 INDEX (birth)
562 ) MAX_ROWS = 1000000;
563 Suppose also that the table has these data and index file sizes:
565 -rw-rw---- 1 mysql mysql 9347072 Aug 19 11:47 person.MYD
567 -rw-rw---- 1 mysql mysql 6066176 Aug 19 11:47 person.MYI
568 Example of myisamchk -dvv output:
570 MyISAM file: person
572 Record format: Packed
573 Character set: latin1_swedish_ci (8)
574 File-version: 1
575 Creation time: 2009-08-19 16:47:41
576 Recover time: 2009-08-19 16:47:56
577 Status: checked,analyzed,optimized keys
578 Auto increment key: 1 Last value: 306688
579 Data records: 306688 Deleted blocks: 0
580 Datafile parts: 306688 Deleted data: 0
581 Datafile pointer (bytes): 4 Keyfile pointer (bytes): 3
582 Datafile length: 9347072 Keyfile length: 6066176
583 Max datafile length: 4294967294 Max keyfile length: 17179868159
584 Recordlength: 54
585 table description:
586 Key Start Len Index Type Rec/key Root Blocksize
587 1 2 4 unique long 1 99328 1024
588 2 6 20 multip. varchar prefix 512 3563520 1024
589 27 20 varchar 512
590 3 48 3 multip. uint24 NULL 306688 6065152 1024
591 Field Start Length Nullpos Nullbit Type
592 1 1 1
593 2 2 4 no zeros
594 3 6 21 varchar
595 4 27 21 varchar
596 5 48 3 1 1 no zeros
597 6 51 3 1 2 no zeros
598 Explanations for the types of information myisamchk produces are given
600 here. “Keyfile” refers to the index file. “Record” and “row” are
601 synonymous, as are “field” and “column.”
602 The initial part of the table description contains these values:
604 · MyISAM file
606 Name of the MyISAM (index) file.
608 · Record format
610 The format used to store table rows. The preceding examples use
612 Fixed length. Other possible values are Compressed and Packed.
613 (Packed corresponds to what SHOW TABLE STATUS reports as Dynamic.)
614 · Chararacter set
616 The table default character set.
618 · File-version
620 Version of MyISAM format. Currently always 1.
622 · Creation time
624 When the data file was created.
626 · Recover time
628 When the index/data file was last reconstructed.
630 · Status
632 Table status flags. Possible values are crashed, open, changed,
634 analyzed, optimized keys, and sorted index pages.
635 · Auto increment key, Last value
637 The key number associated the table's AUTO_INCREMENT column, and
639 the most recently generated value for this column. These fields do
640 not appear if there is no such column.
641 · Data records
643 The number of rows in the table.
645 · Deleted blocks
647 How many deleted blocks still have reserved space. You can optimize
649 your table to minimize this space. See Section 7.6.4, “MyISAM Table
650 Optimization”.
651 · Datafile parts
653 For dynamic-row format, this indicates how many data blocks there
655 are. For an optimized table without fragmented rows, this is the
656 same as Data records.
657 · Deleted data
659 How many bytes of unreclaimed deleted data there are. You can
661 optimize your table to minimize this space. See Section 7.6.4,
662 “MyISAM Table Optimization”.
663 · Datafile pointer
665 The size of the data file pointer, in bytes. It is usually 2, 3, 4,
667 or 5 bytes. Most tables manage with 2 bytes, but this cannot be
668 controlled from MySQL yet. For fixed tables, this is a row address.
669 For dynamic tables, this is a byte address.
670 · Keyfile pointer
672 The size of the index file pointer, in bytes. It is usually 1, 2,
674 or 3 bytes. Most tables manage with 2 bytes, but this is calculated
675 automatically by MySQL. It is always a block address.
676 · Max datafile length
678 How long the table data file can become, in bytes.
680 · Max keyfile length
682 How long the table index file can become, in bytes.
684 · Recordlength
686 How much space each row takes, in bytes.
688 The table description part of the output includes a list of all keys in
690 the table. For each key, myisamchk displays some low-level information:
691 · Key
693 This key's number. This value is shown only for the first column of
695 the key. If this value is missing, the line corresponds to the
696 second or later column of a multiple-column key. For the table
697 shown in the example, there are two table description lines for the
698 second index. This indicates that it is a multiple-part index with
699 two parts.
700 · Start
702 Where in the row this portion of the index starts.
704 · Len
706 How long this portion of the index is. For packed numbers, this
708 should always be the full length of the column. For strings, it may
709 be shorter than the full length of the indexed column, because you
710 can index a prefix of a string column. The total length of a
711 multiple-part key is the sum of the Len values for all key parts.
712 · Index
714 Whether a key value can exist multiple times in the index. Possible
716 values are unique or multip. (multiple).
717 · Type
719 What data type this portion of the index has. This is a MyISAM data
721 type with the possible values packed, stripped, or empty.
722 · Root
724 Address of the root index block.
726 · Blocksize
728 The size of each index block. By default this is 1024, but the
730 value may be changed at compile time when MySQL is built from
731 source.
732 · Rec/key
734 This is a statistical value used by the optimizer. It tells how
736 many rows there are per value for this index. A unique index always
737 has a value of 1. This may be updated after a table is loaded (or
738 greatly changed) with myisamchk -a. If this is not updated at all,
739 a default value of 30 is given.
740 The last part of the output provides information about each column:
742 · Field
744 The column number.
746 · Start
748 The byte position of the column within table rows.
750 · Length
752 The length of the column in bytes.
754 · Nullpos, Nullbit
756 For columns that can be NULL, MyISAM stores NULL values as a flag
758 in a byte. Depending on how many nullable columns there are, there
759 can be one or more bytes used for this purpose. The Nullpos and
760 Nullbit values, if nonempty, indicate which byte and bit contains
761 that flag indicating whether the column is NULL.
762 The position and number of bytes used to store NULL flags is shown
764 in the line for field 1. This is why there are six Field lines for
765 the person table even though it has only five columns.
766 · Type
768 The data type. The value may contain any of the following
770 descriptors:
771 · constant
773 All rows have the same value.
775 · no endspace
777 Do not store endspace.
779 · no endspace, not_always
781 Do not store endspace and do not do endspace compression for
783 all values.
784 · no endspace, no empty
786 Do not store endspace. Do not store empty values.
788 · table-lookup
790 The column was converted to an ENUM.
792 · zerofill(N)
794 The most significant N bytes in the value are always 0 and are
796 not stored.
797 · no zeros
799 Do not store zeros.
801 · always zero
803 Zero values are stored using one bit.
805 · Huff tree
807 The number of the Huffman tree associated with the column.
809 · Bits
811 The number of bits used in the Huffman tree.
813 The Huff tree and Bits fields are displayed if the table has been
815 compressed with myisampack. See myisampack(1), for an example of this
816 information.
817 Example of myisamchk -eiv output:
819 Checking MyISAM file: person
821 Data records: 306688 Deleted blocks: 0
822 - check file-size
823 - check record delete-chain
824 No recordlinks
825 - check key delete-chain
826 block_size 1024:
827 - check index reference
828 - check data record references index: 1
829 Key: 1: Keyblocks used: 98% Packed: 0% Max levels: 3
830 - check data record references index: 2
831 Key: 2: Keyblocks used: 99% Packed: 97% Max levels: 3
832 - check data record references index: 3
833 Key: 3: Keyblocks used: 98% Packed: -14% Max levels: 3
834 Total: Keyblocks used: 98% Packed: 89%
835 - check records and index references
836 *** LOTS OF ROW NUMBERS DELETED ***
837 Records: 306688 M.recordlength: 25 Packed: 83%
838 Recordspace used: 97% Empty space: 2% Blocks/Record: 1.00
839 Record blocks: 306688 Delete blocks: 0
840 Record data: 7934464 Deleted data: 0
841 Lost space: 256512 Linkdata: 1156096
842 User time 43.08, System time 1.68
843 Maximum resident set size 0, Integral resident set size 0
844 Non-physical pagefaults 0, Physical pagefaults 0, Swaps 0
845 Blocks in 0 out 7, Messages in 0 out 0, Signals 0
846 Voluntary context switches 0, Involuntary context switches 0
847 Maximum memory usage: 1046926 bytes (1023k)
848 myisamchk -eiv output includes the following information:
850 · Data records
852 The number of rows in the table.
854 · Deleted blocks
856 How many deleted blocks still have reserved space. You can optimize
858 your table to minimize this space. See Section 7.6.4, “MyISAM Table
859 Optimization”.
860 · Key
862 The key number.
864 · Keyblocks used
866 What percentage of the keyblocks are used. When a table has just
868 been reorganized with myisamchk, the values are very high (very
869 near theoretical maximum).
870 · Packed
872 MySQL tries to pack key values that have a common suffix. This can
874 only be used for indexes on CHAR and VARCHAR columns. For long
875 indexed strings that have similar leftmost parts, this can
876 significantly reduce the space used. In the preceding example, the
877 second key is 40 bytes long and a 97% reduction in space is
878 achieved.
879 · Max levels
881 How deep the B-tree for this key is. Large tables with long key
883 values get high values.
884 · Records
886 How many rows are in the table.
888 · M.recordlength
890 The average row length. This is the exact row length for tables
892 with fixed-length rows, because all rows have the same length.
893 · Packed
895 MySQL strips spaces from the end of strings. The Packed value
897 indicates the percentage of savings achieved by doing this.
898 · Recordspace used
900 What percentage of the data file is used.
902 · Empty space
904 What percentage of the data file is unused.
906 · Blocks/Record
908 Average number of blocks per row (that is, how many links a
910 fragmented row is composed of). This is always 1.0 for fixed-format
911 tables. This value should stay as close to 1.0 as possible. If it
912 gets too large, you can reorganize the table. See Section 7.6.4,
913 “MyISAM Table Optimization”.
914 · Recordblocks
916 How many blocks (links) are used. For fixed-format tables, this is
918 the same as the number of rows.
919 · Deleteblocks
921 How many blocks (links) are deleted.
923 · Recorddata
925 How many bytes in the data file are used.
927 · Deleted data
929 How many bytes in the data file are deleted (unused).
931 · Lost space
933 If a row is updated to a shorter length, some space is lost. This
935 is the sum of all such losses, in bytes.
936 · Linkdata
938 When the dynamic table format is used, row fragments are linked
940 with pointers (4 to 7 bytes each). Linkdata is the sum of the
941 amount of storage used by all such pointers.
942
944 Memory allocation is important when you run myisamchk. myisamchk uses
945 no more memory than its memory-related variables are set to. If you are
946 going to use myisamchk on very large tables, you should first decide
947 how much memory you want it to use. The default is to use only about
948 3MB to perform repairs. By using larger values, you can get myisamchk
949 to operate faster. For example, if you have more than 512MB RAM
950 available, you could use options such as these (in addition to any
951 other options you might specify):
952 shell> myisamchk --myisam_sort_buffer_size=256M \
954 --key_buffer_size=512M \
955 --read_buffer_size=64M \
956 --write_buffer_size=64M ...
957 Using --myisam_sort_buffer_size=16M is probably enough for most cases.
959 Be aware that myisamchk uses temporary files in TMPDIR. If TMPDIR
961 points to a memory file system, out of memory errors can easily occur.
962 If this happens, run myisamchk with the --tmpdir=path option to specify
963 a directory located on a file system that has more space.
964 When performing repair operations, myisamchk also needs a lot of disk
966 space:
967 · Twice the size of the data file (the original file and a copy).
969 This space is not needed if you do a repair with --quick; in this
970 case, only the index file is re-created. This space must be
971 available on the same file system as the original data file, as the
972 copy is created in the same directory as the original.
973 · Space for the new index file that replaces the old one. The old
975 index file is truncated at the start of the repair operation, so
976 you usually ignore this space. This space must be available on the
977 same file system as the original data file.
978 · When using --recover or --sort-recover (but not when using
980 --safe-recover), you need space on disk for sorting. This space is
981 allocated in the temporary directory (specified by TMPDIR or
982 --tmpdir=path). The following formula yields the amount of space
983 required:
984 (largest_key + row_pointer_length) * number_of_rows * 2
986 You can check the length of the keys and the row_pointer_length
988 with myisamchk -dv tbl_name (see the section called “OBTAINING
989 TABLE INFORMATION WITH MYISAMCHK”). The row_pointer_length and
990 number_of_rows values are the Datafile pointer and Data records
991 values in the table description. To determine the largest_key
992 value, check the Key lines in the table description. The Len column
993 indicates the number of bytes for each key part. For a
994 multiple-column index, the key size is the sum of the Len values
995 for all key parts.
996 If you have a problem with disk space during repair, you can try
998 --safe-recover instead of --recover.
999
1001 Copyright © 1997, 2013, Oracle and/or its affiliates. All rights
1002 reserved.
1003 This documentation is free software; you can redistribute it and/or
1005 modify it only under the terms of the GNU General Public License as
1006 published by the Free Software Foundation; version 2 of the License.
1007 This documentation is distributed in the hope that it will be useful,
1009 but WITHOUT ANY WARRANTY; without even the implied warranty of
1010 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1011 General Public License for more details.
1012 You should have received a copy of the GNU General Public License along
1014 with the program; if not, write to the Free Software Foundation, Inc.,
1015 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see
1016 http://www.gnu.org/licenses/.
1017
1020 For more information, please refer to the MySQL Reference Manual, which
1021 may already be installed locally and which is also available online at
1022 http://dev.mysql.com/doc/.
1023
1025 Oracle Corporation (http://dev.mysql.com/).
1026MySQL 5.1 11/04/2013 MYISAMCHK(1)