1MYISAMCHK(1)                MariaDB Database System               MYISAMCHK(1)
2
3
4

NAME

6       myisamchk - MyISAM table-maintenance utility
7

SYNOPSIS

9       myisamchk [options] tbl_name ...
10

DESCRIPTION

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
16       The use of myisamchk with partitioned tables is not supported.
17
18           Caution
19           It is best to make a backup of a table before performing a table
20           repair operation; under some circumstances the operation might
21           cause data loss. Possible causes include but are not limited to
22           file system errors.
23
24       Invoke myisamchk like this:
25
26           shell> myisamchk [options] tbl_name ...
27
28       The options specify what you want myisamchk to do. They are described
29       in the following sections. You can also get a list of options by
30       invoking myisamchk --help.
31
32       With no options, myisamchk simply checks your table as the default
33       operation. To get more information or to tell myisamchk to take
34       corrective action, specify options as described in the following
35       discussion.
36
37       tbl_name is the database table you want to check or repair. If you run
38       myisamchk somewhere other than in the database directory, you must
39       specify the path to the database directory, because myisamchk has no
40       idea where the database is located. In fact, myisamchk does not
41       actually care whether the files you are working on are located in a
42       database directory. You can copy the files that correspond to a
43       database table into some other location and perform recovery operations
44       on them there.
45
46       You can name several tables on the myisamchk command line if you wish.
47       You can also specify a table by naming its index file (the file with
48       the .MYI suffix). This allows you to specify all tables in a directory
49       by using the pattern *.MYI. For example, if you are in a database
50       directory, you can check all the MyISAM tables in that directory like
51       this:
52
53           shell> myisamchk *.MYI
54
55       If you are not in the database directory, you can check all the tables
56       there by specifying the path to the directory:
57
58           shell> myisamchk /path/to/database_dir/*.MYI
59
60       You can even check all tables in all databases by specifying a wildcard
61       with the path to the MariaDB data directory:
62
63           shell> myisamchk /path/to/datadir/*/*.MYI
64
65       The recommended way to quickly check all MyISAM tables is:
66
67           shell> myisamchk --silent --fast /path/to/datadir/*/*.MYI
68
69       If you want to check all MyISAM tables and repair any that are
70       corrupted, you can use the following command:
71
72           shell> myisamchk --silent --force --fast --update-state \
73                     --key_buffer_size=64M --sort_buffer_size=64M \
74                     --read_buffer_size=1M --write_buffer_size=1M \
75                     /path/to/datadir/*/*.MYI
76
77       This command assumes that you have more than 64MB free. For more
78       information about memory allocation with myisamchk, see the section
79       called “MYISAMCHK MEMORY USAGE”.
80
81           Important
82           You must ensure that no other program is using the tables while you
83           are running myisamchk. The most effective means of doing so is to
84           shut down the MariaDB server while running myisamchk, or to lock
85           all tables that myisamchk is being used on.
86
87           Otherwise, when you run myisamchk, it may display the following
88           error message:
89
90               warning: clients are using or haven´t closed the table properly
91
92           This means that you are trying to check a table that has been
93           updated by another program (such as the mysqld server) that hasn´t
94           yet closed the file or that has died without closing the file
95           properly, which can sometimes lead to the corruption of one or more
96           MyISAM tables.
97
98           If mysqld is running, you must force it to flush any table
99           modifications that are still buffered in memory by using FLUSH
100           TABLES. You should then ensure that no one is using the tables
101           while you are running myisamchk
102
103           However, the easiest way to avoid this problem is to use CHECK
104           TABLE instead of myisamchk to check tables.
105
106       myisamchk supports the following options, which can be specified on the
107       command line or in the [myisamchk] option file group.
108

MYISAMCHK GENERAL OPTIONS

110       The options described in this section can be used for any type of table
111       maintenance operation performed by myisamchk. The sections following
112       this one describe options that pertain only to specific operations,
113       such as table checking or repairing.
114
115       ·   --help, -?
116
117           Display a help message and exit. Options are grouped by type of
118           operation.
119
120       ·   --HELP, -H
121
122           Display a help message and exit. Options are presented in a single
123           list.
124
125       ·   --debug=debug_options, -# debug_options
126
127           Write a debugging log. A typical debug_options string is
128           ´d:t:o,file_name´. The default is ´d:t:o,/tmp/myisamchk.trace´.
129
130       ·   --silent, -s
131
132           Silent mode. Write output only when errors occur. You can use -s
133           twice (-ss) to make myisamchk very silent.
134
135       ·   --verbose, -v
136
137           Verbose mode. Print more information about what the program does.
138           This can be used with -d and -e. Use -v multiple times (-vv, -vvv)
139           for even more output.
140
141       ·   --version, -V
142
143           Display version information and exit.
144
145       ·   --wait, -w
146
147           Instead of terminating with an error if the table is locked, wait
148           until the table is unlocked before continuing. If you are running
149           mysqld with external locking disabled, the table can be locked only
150           by another myisamchk command.
151
152       ·   --print-defaults
153
154           Print the program argument list and exit.
155
156       ·   --no-defaults
157
158           Don't read default options from any option file.
159
160       ·   --defaults-file=#
161
162           Only read default options from the given file.
163
164       ·   --defaults-extra-file=#
165
166           Read this file after the global files are read.
167
168       You can also set the following variables by using --var_name=value
169       syntax:
170
171       ┌─────────────────────┬───────────────────┐
172Variable             Default Value     
173       ├─────────────────────┼───────────────────┤
174       │decode_bits          │ 9                 │
175       ├─────────────────────┼───────────────────┤
176       │ft_max_word_len      │ version-dependent │
177       ├─────────────────────┼───────────────────┤
178       │ft_min_word_len      │ 4                 │
179       ├─────────────────────┼───────────────────┤
180       │ft_stopword_file     │ built-in list     │
181       ├─────────────────────┼───────────────────┤
182       │key_buffer_size      │ 523264            │
183       ├─────────────────────┼───────────────────┤
184       │key_cache_block_size │ 1024              │
185       ├─────────────────────┼───────────────────┤
186       │myisam_block_size    │ 1024              │
187       ├─────────────────────┼───────────────────┤
188       │read_buffer_size     │ 262136            │
189       ├─────────────────────┼───────────────────┤
190       │sort_buffer_size     │ 2097144           │
191       ├─────────────────────┼───────────────────┤
192       │sort_key_blocks      │ 16                │
193       ├─────────────────────┼───────────────────┤
194       │stats_method         │ nulls_unequal     │
195       ├─────────────────────┼───────────────────┤
196       │write_buffer_size    │ 262136            │
197       └─────────────────────┴───────────────────┘
198
199       The possible myisamchk variables and their default values can be
200       examined with myisamchk --help:
201
202       sort_buffer_size is used when the keys are repaired by sorting keys,
203       which is the normal case when you use --recover.
204
205       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
210       ·   You use --safe-recover.
211
212       ·   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
220       Repairing through the key buffer takes much less disk space than using
221       sorting, but is also much slower.
222
223       If you want a faster repair, set the key_buffer_size and
224       sort_buffer_size variables to about 25% of your available memory. You
225       can set both variables to large values, because only one of them is
226       used at a time.
227
228       myisam_block_size is the size used for index blocks.
229
230       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 7.4.7, “MyISAM Index Statistics Collection”.
235
236       ft_min_word_len and ft_max_word_len indicate the minimum and maximum
237       word length for FULLTEXT indexes.  ft_stopword_file names the stopword
238       file. These need to be set under the following circumstances.
239
240       If you use myisamchk to perform an operation that modifies table
241       indexes (such as repair or analyze), the FULLTEXT indexes are rebuilt
242       using the default full-text parameter values for minimum and maximum
243       word length and the stopword file unless you specify otherwise. This
244       can result in queries failing.
245
246       The problem occurs because these parameters are known only by the
247       server. They are not stored in MyISAM index files. To avoid the problem
248       if you have modified the minimum or maximum word length or the stopword
249       file in the server, specify the same ft_min_word_len, ft_max_word_len,
250       and ft_stopword_file values to myisamchk that you use for mysqld. For
251       example, if you have set the minimum word length to 3, you can repair a
252       table with myisamchk like this:
253
254           shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI
255
256       To ensure that myisamchk and the server use the same values for
257       full-text parameters, you can place each one in both the [mysqld] and
258       [myisamchk] sections of an option file:
259
260           [mysqld]
261           ft_min_word_len=3
262           [myisamchk]
263           ft_min_word_len=3
264
265       An alternative to using myisamchk is to use the REPAIR TABLE, ANALYZE
266       TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements are performed
267       by the server, which knows the proper full-text parameter values to
268       use.
269

MYISAMCHK CHECK OPTIONS

271       myisamchk supports the following options for table checking operations:
272
273       ·   --check, -c
274
275           Check the table for errors. This is the default operation if you
276           specify no option that selects an operation type explicitly.
277
278       ·   --check-only-changed, -C
279
280           Check only tables that have changed since the last check.
281
282       ·   --extend-check, -e
283
284           Check the table very thoroughly. This is quite slow if the table
285           has many indexes. This option should only be used in extreme cases.
286           Normally, myisamchk or myisamchk --medium-check should be able to
287           determine whether there are any errors in the table.
288
289           If you are using --extend-check and have plenty of memory, setting
290           the key_buffer_size variable to a large value helps the repair
291           operation run faster.
292
293           For a description of the output format, see the section called
294           “MYISAMCHK TABLE INFORMATION”.
295
296       ·   --fast, -F
297
298           Check only tables that haven´t been closed properly.
299
300       ·   --force, -f
301
302           Do a repair operation automatically if myisamchk finds any errors
303           in the table. The repair type is the same as that specified with
304           the --recover or -r option. States will be updated as with
305           --update-state.
306
307       ·   --information, -i
308
309           Print informational statistics about the table that is checked.
310
311       ·   --medium-check, -m
312
313           Do a check that is faster than an --extend-check operation. This
314           finds only 99.99% of all errors, which should be good enough in
315           most cases.
316
317       ·   --read-only, -T
318
319           Do not mark the table as checked. This is useful if you use
320           myisamchk to check a table that is in use by some other application
321           that does not use locking, such as mysqld when run with external
322           locking disabled.
323
324       ·   --update-state, -U
325
326           Store information in the .MYI file to indicate when the table was
327           checked and whether the table crashed. This should be used to get
328           full benefit of the --check-only-changed option, but you shouldn´t
329           use this option if the mysqld server is using the table and you are
330           running it with external locking disabled.
331

MYISAMCHK REPAIR OPTIONS

333       myisamchk supports the following options for table repair operations
334       (operations performed when an option such as --recover or
335       --safe-recover is given):
336
337       ·   --backup, -B
338
339           Make a backup of the .MYD file as file_name-time.BAK
340
341       ·   --character-sets-dir=path
342
343           The directory where character sets are installed.
344
345       ·   --correct-checksum
346
347           Correct the checksum information for the table.
348
349       ·   --create-missing-keys
350
351           Create missing keys. This assumes that the data file is correct and
352           that the number of rows stored in the index file is correct.
353           Enables --quick.
354
355
356       ·   --data-file-length=len, -D len
357
358           The maximum length of the data file (when re-creating data file
359           when it is “full”).
360
361       ·   --extend-check, -e
362
363           Do a repair that tries to recover every possible row from the data
364           file. Normally, this also finds a lot of garbage rows. Do not use
365           this option unless you are desperate.
366
367           For a description of the output format, see the section called
368           “MYISAMCHK TABLE INFORMATION”.
369
370       ·   --force, -f
371
372           Overwrite old intermediate files (files with names like
373           tbl_name.TMD) instead of aborting. Add another --force to avoid
374           'myisam_sort_buffer_size is too small' errors. In this case we will
375           attempt to do the repair with the given myisam_sort_buffer_size and
376           dynamically allocate as many management buffers as needed.
377
378       ·   --keys-used=val, -k val
379
380           For myisamchk, the option value is a bit-value that indicates which
381           indexes to update. Each binary bit of the option value corresponds
382           to a table index, where the first index is bit 0. An option value
383           of 0 disables updates to all indexes, which can be used to get
384           faster inserts. Deactivated indexes can be reactivated by using
385           myisamchk -r.
386
387       ·   --max-record-length=len
388
389           Skip rows larger than the given length if myisamchk cannot allocate
390           memory to hold them.
391
392       ·   --parallel-recover, -p
393
394           Use the same technique as -r and -n, but create all the keys in
395           parallel, using different threads.  This is beta-quality code. Use
396           at your own risk!
397
398       ·   --quick, -q
399
400           Achieve a faster repair by modifying only the index file, not the
401           data file. You can specify this option twice to force myisamchk to
402           modify the original data file in case of duplicate keys. NOTE:
403           Tables where the data file is corrupted can't be fixed with this
404           option.
405
406       ·   --recover, -r
407
408           Do a repair that can fix almost any problem except unique keys that
409           are not unique (which is an extremely unlikely error with MyISAM
410           tables). If you want to recover a table, this is the option to try
411           first. You should try --safe-recover only if myisamchk reports that
412           the table cannot be recovered using --recover. (In the unlikely
413           case that --recover fails, the data file remains intact.)
414
415           If you have lots of memory, you should increase the value of
416           sort_buffer_size.
417
418       ·   --safe-recover, -o
419
420           Do a repair using an old recovery method that reads through all
421           rows in order and updates all index trees based on the rows found.
422           This is an order of magnitude slower than --recover, but can handle
423           a couple of very unlikely cases that --recover cannot. This
424           recovery method also uses much less disk space than --recover.
425           Normally, you should repair first using --recover, and then with
426           --safe-recover only if --recover fails.
427
428           If you have lots of memory, you should increase the value of
429           key_buffer_size.
430
431       ·   --set-collation=name
432
433           Specify the collation to use for sorting table indexes. The
434           character set name is implied by the first part of the collation
435           name.
436
437       ·   --sort-recover, -n
438
439           Force myisamchk to use sorting to resolve the keys even if the
440           temporary files would be very large.
441
442       ·   --tmpdir=path, -t path
443
444           The path of the directory to be used for storing temporary files.
445           If this is not set, myisamchk uses the value of the TMPDIR
446           environment variable.  tmpdir can be set to a list of directory
447           paths that are used successively in round-robin fashion for
448           creating temporary files. The separator character between directory
449           names is the colon (“:”) on Unix and the semicolon (“;”) on
450           Windows, NetWare, and OS/2.
451
452       ·   --unpack, -u
453
454           Unpack a table that was packed with myisampack.
455

OTHER MYISAMCHK OPTIONS

457       myisamchk supports the following options for actions other than table
458       checks and repairs:
459
460       ·   --analyze, -a
461
462           Analyze the distribution of key values. This improves join
463           performance by enabling the join optimizer to better choose the
464           order in which to join the tables and which indexes it should use.
465           To obtain information about the key distribution, use a myisamchk
466           --description --verbose tbl_name command or the SHOW INDEX FROM
467           tbl_name statement.
468
469       ·   --block-search=offset, -b offset
470
471           Find the record that a block at the given offset belongs to.
472
473       ·   --description, -d
474
475           Print some descriptive information about the table. Specifying the
476           --verbose option once or twice produces additional information. See
477           the section called “MYISAMCHK TABLE INFORMATION”.
478
479       ·   --set-auto-increment[=value], -A[value]
480
481           Force AUTO_INCREMENT numbering for new records to start at the
482           given value (or higher, if there are existing records with
483           AUTO_INCREMENT values this large). If value is not specified,
484           AUTO_INCREMENT numbers for new records begin with the largest value
485           currently in the table, plus one.
486
487       ·   --sort-index, -S
488
489           Sort the index tree blocks in high-low order. This optimizes seeks
490           and makes table scans that use indexes faster.
491
492       ·   --sort-records=N, -R N
493
494           Sort records according to a particular index. This makes your data
495           much more localized and may speed up range-based SELECT and ORDER
496           BY operations that use this index. (The first time you use this
497           option to sort a table, it may be very slow.) To determine a
498           table´s index numbers, use SHOW INDEX, which displays a table´s
499           indexes in the same order that myisamchk sees them. Indexes are
500           numbered beginning with 1.
501
502           If keys are not packed (PACK_KEYS=0), they have the same length, so
503           when myisamchk sorts and moves records, it just overwrites record
504           offsets in the index. If keys are packed (PACK_KEYS=1), myisamchk
505           must unpack key blocks first, then re-create indexes and pack the
506           key blocks again. (In this case, re-creating indexes is faster than
507           updating offsets for each index.)
508
509       ·   --stats-method=name
510
511           Specifies how index statistics collection code should treat NULLs.
512           Possible values of name are "nulls_unequal" (default),
513           "nulls_equal" (emulate MySQL 4 behavior), and "nulls_ignored".
514

MYISAMCHK TABLE INFORMATION

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
520       ·   myisamchk -d tbl_name
521
522           Runs myisamchk in “describe mode” to produce a description of your
523           table. If you start the MariaDB 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
528       ·   myisamchk -dv tbl_name
529
530           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
534       ·   myisamchk -eis tbl_name
535
536           Shows only the most important information from a table. This
537           operation is slow because it must read the entire table.
538
539       ·   myisamchk -eiv tbl_name
540
541           This is like -eis, but tells you what is being done.
542
543       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
547       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
552           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
564       Suppose also that the table has these data and index file sizes:
565
566           -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
569       Example of myisamchk -dvv output:
570
571           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
599       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
603       The initial part of the table description contains these values:
604
605       ·   MyISAM file
606
607           Name of the MyISAM (index) file.
608
609       ·   Record format
610
611           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
615       ·   Chararacter set
616
617           The table default character set.
618
619       ·   File-version
620
621           Version of MyISAM format. Currently always 1.
622
623       ·   Creation time
624
625           When the data file was created.
626
627       ·   Recover time
628
629           When the index/data file was last reconstructed.
630
631       ·   Status
632
633           Table status flags. Possible values are crashed, open, changed,
634           analyzed, optimized keys, and sorted index pages.
635
636       ·   Auto increment key, Last value
637
638           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
642       ·   Data records
643
644           The number of rows in the table.
645
646       ·   Deleted blocks
647
648           How many deleted blocks still have reserved space. You can optimize
649           your table to minimize this space. See Section 6.6.4, “MyISAM Table
650           Optimization”.
651
652       ·   Datafile parts
653
654           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
658       ·   Deleted data
659
660           How many bytes of unreclaimed deleted data there are. You can
661           optimize your table to minimize this space. See Section 6.6.4,
662           “MyISAM Table Optimization”.
663
664       ·   Datafile pointer
665
666           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 MariaDB yet. For fixed tables, this is a row
669           address. For dynamic tables, this is a byte address.
670
671       ·   Keyfile pointer
672
673           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 MariaDB. It is always a block address.
676
677       ·   Max datafile length
678
679           How long the table data file can become, in bytes.
680
681       ·   Max keyfile length
682
683           How long the table index file can become, in bytes.
684
685       ·   Recordlength
686
687           How much space each row takes, in bytes.
688
689       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
692       ·   Key
693
694           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
701       ·   Start
702
703           Where in the row this portion of the index starts.
704
705       ·   Len
706
707           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
713       ·   Index
714
715           Whether a key value can exist multiple times in the index. Possible
716           values are unique or multip.  (multiple).
717
718       ·   Type
719
720           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
723       ·   Root
724
725           Address of the root index block.
726
727       ·   Blocksize
728
729           The size of each index block. By default this is 1024, but the
730           value may be changed at compile time when MariaDB is built from
731           source.
732
733       ·   Rec/key
734
735           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
741       The last part of the output provides information about each column:
742
743       ·   Field
744
745           The column number.
746
747       ·   Start
748
749           The byte position of the column within table rows.
750
751       ·   Length
752
753           The length of the column in bytes.
754
755       ·   Nullpos, Nullbit
756
757           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
763           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
767       ·   Type
768
769           The data type. The value may contain any of the following
770           descriptors:
771
772           ·   constant
773
774               All rows have the same value.
775
776           ·   no endspace
777
778               Do not store endspace.
779
780           ·   no endspace, not_always
781
782               Do not store endspace and do not do endspace compression for
783               all values.
784
785           ·   no endspace, no empty
786
787               Do not store endspace. Do not store empty values.
788
789           ·   table-lookup
790
791               The column was converted to an ENUM.
792
793           ·   zerofill(N)
794
795               The most significant N bytes in the value are always 0 and are
796               not stored.
797
798           ·   no zeros
799
800               Do not store zeros.
801
802           ·   always zero
803
804               Zero values are stored using one bit.
805
806       ·   Huff tree
807
808           The number of the Huffman tree associated with the column.
809
810       ·   Bits
811
812           The number of bits used in the Huffman tree.
813
814       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
818       Example of myisamchk -eiv output:
819
820           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
849       myisamchk -eiv output includes the following information:
850
851       ·   Data records
852
853           The number of rows in the table.
854
855       ·   Deleted blocks
856
857           How many deleted blocks still have reserved space. You can optimize
858           your table to minimize this space. See Section 6.6.4, “MyISAM Table
859           Optimization”.
860
861       ·   Key
862
863           The key number.
864
865       ·   Keyblocks used
866
867           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
871       ·   Packed
872
873           MariaDB tries to pack key values that have a common suffix. This
874           can 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
880       ·   Max levels
881
882           How deep the B-tree for this key is. Large tables with long key
883           values get high values.
884
885       ·   Records
886
887           How many rows are in the table.
888
889       ·   M.recordlength
890
891           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
894       ·   Packed
895
896           MariaDB strips spaces from the end of strings. The Packed value
897           indicates the percentage of savings achieved by doing this.
898
899       ·   Recordspace used
900
901           What percentage of the data file is used.
902
903       ·   Empty space
904
905           What percentage of the data file is unused.
906
907       ·   Blocks/Record
908
909           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 6.6.4,
913           “MyISAM Table Optimization”.
914
915       ·   Recordblocks
916
917           How many blocks (links) are used. For fixed-format tables, this is
918           the same as the number of rows.
919
920       ·   Deleteblocks
921
922           How many blocks (links) are deleted.
923
924       ·   Recorddata
925
926           How many bytes in the data file are used.
927
928       ·   Deleted data
929
930           How many bytes in the data file are deleted (unused).
931
932       ·   Lost space
933
934           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
937       ·   Linkdata
938
939           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

MYISAMCHK MEMORY USAGE

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 32MB RAM, you
950       could use options such as these (in addition to any other options you
951       might specify):
952
953           shell> myisamchk --sort_buffer_size=16M \
954                      --key_buffer_size=16M \
955                      --read_buffer_size=1M \
956                      --write_buffer_size=1M ...
957
958       Using --sort_buffer_size=16M should probably be enough for most cases.
959
960       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
965       When performing repair operations, myisamchk also needs a lot of disk
966       space:
967
968       ·   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
974       ·   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
979       ·   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
985               (largest_key + row_pointer_length) × number_of_rows × 2
986
987           You can check the length of the keys and the row_pointer_length
988           with myisamchk -dv tbl_name (see the section called “MYISAMCHK
989           TABLE INFORMATION”). The row_pointer_length and number_of_rows
990           values are the Datafile pointer and Data records values in the
991           table description. To determine the largest_key value, check the
992           Key lines in the table description. The Len column indicates the
993           number of bytes for each key part. For a multiple-column index, the
994           key size is the sum of the Len values for all key parts.
995
996       If you have a problem with disk space during repair, you can try
997       --safe-recover instead of --recover.
998
1000       Copyright 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc.,
1001       2010-2015 MariaDB Foundation
1002
1003       This documentation is free software; you can redistribute it and/or
1004       modify it only under the terms of the GNU General Public License as
1005       published by the Free Software Foundation; version 2 of the License.
1006
1007       This documentation is distributed in the hope that it will be useful,
1008       but WITHOUT ANY WARRANTY; without even the implied warranty of
1009       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
1010       General Public License for more details.
1011
1012       You should have received a copy of the GNU General Public License along
1013       with the program; if not, write to the Free Software Foundation, Inc.,
1014       51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA or see
1015       http://www.gnu.org/licenses/.
1016
1017

SEE ALSO

1019       For more information, please refer to the MariaDB Knowledge Base,
1020       available online at https://mariadb.com/kb/
1021

AUTHOR

1023       MariaDB Foundation (http://www.mariadb.org/).
1024
1025
1026
1027MariaDB 10.4                     28 March 2019                    MYISAMCHK(1)
Impressum