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 The use of myisamchk with partitioned tables is not supported.
17 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 Invoke myisamchk like this:
25 shell> myisamchk [options] tbl_name ...
27 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 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 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 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 shell> myisamchk *.MYI
54 If you are not in the database directory, you can check all the tables
56 there by specifying the path to the directory:
57 shell> myisamchk /path/to/database_dir/*.MYI
59 You can even check all tables in all databases by specifying a wildcard
61 with the path to the MySQL data directory:
62 shell> myisamchk /path/to/datadir/*/*.MYI
64 The recommended way to quickly check all MyISAM tables is:
66 shell> myisamchk --silent --fast /path/to/datadir/*/*.MYI
68 If you want to check all MyISAM tables and repair any that are
70 corrupted, you can use the following command:
71 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 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 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 MySQL server while running myisamchk, or to lock all
85 tables that myisamchk is being used on.
86 Otherwise, when you run myisamchk, it may display the following
88 error message:
89 warning: clients are using or haven´t closed the table properly
91 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 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 However, the easiest way to avoid this problem is to use CHECK
104 TABLE instead of myisamchk to check tables. See Section 12.4.2.3,
105 “CHECK TABLE Syntax”.
106 myisamchk supports the following options, which can be specified on the
108 command line or in the [myisamchk] option file group. myisamchk also
109 supports the options for processing option files described at
110 Section 4.2.3.3.1, “Command-Line Options that Affect Option-File
111 Handling”.
112
114 The options described in this section can be used for any type of table
115 maintenance operation performed by myisamchk. The sections following
116 this one describe options that pertain only to specific operations,
117 such as table checking or repairing.
118 · --help, -?
120 Display a help message and exit. Options are grouped by type of
122 operation.
123 · --HELP, -H
125 Display a help message and exit. Options are presented in a single
127 list.
128 · --debug=debug_options, -# debug_options
130 Write a debugging log. A typical debug_options string is
132 ´d:t:o,file_name´. The default is ´d:t:o,/tmp/myisamchk.trace´.
133 · --silent, -s
135 Silent mode. Write output only when errors occur. You can use -s
137 twice (-ss) to make myisamchk very silent.
138 · --verbose, -v
140 Verbose mode. Print more information about what the program does.
142 This can be used with -d and -e. Use -v multiple times (-vv, -vvv)
143 for even more output.
144 · --version, -V
146 Display version information and exit.
148 · --wait, -w
150 Instead of terminating with an error if the table is locked, wait
152 until the table is unlocked before continuing. If you are running
153 mysqld with external locking disabled, the table can be locked only
154 by another myisamchk command.
155 You can also set the following variables by using --var_name=value
157 syntax:
158 ┌──────────────────┬───────────────────┐
160 │Variable │ Default Value │
161 ├──────────────────┼───────────────────┤
162 │decode_bits │ 9 │
163 ├──────────────────┼───────────────────┤
164 │ft_max_word_len │ version-dependent │
165 ├──────────────────┼───────────────────┤
166 │ft_min_word_len │ 4 │
167 ├──────────────────┼───────────────────┤
168 │ft_stopword_file │ built-in list │
169 ├──────────────────┼───────────────────┤
170 │key_buffer_size │ 523264 │
171 ├──────────────────┼───────────────────┤
172 │myisam_block_size │ 1024 │
173 ├──────────────────┼───────────────────┤
174 │read_buffer_size │ 262136 │
175 ├──────────────────┼───────────────────┤
176 │sort_buffer_size │ 2097144 │
177 ├──────────────────┼───────────────────┤
178 │sort_key_blocks │ 16 │
179 ├──────────────────┼───────────────────┤
180 │stats_method │ nulls_unequal │
181 ├──────────────────┼───────────────────┤
182 │write_buffer_size │ 262136 │
183 └──────────────────┴───────────────────┘
184 The possible myisamchk variables and their default values can be
186 examined with myisamchk --help:
187 sort_buffer_size is used when the keys are repaired by sorting keys,
189 which is the normal case when you use --recover.
190 key_buffer_size is used when you are checking the table with
192 --extend-check or when the keys are repaired by inserting keys row by
193 row into the table (like when doing normal inserts). Repairing through
194 the key buffer is used in the following cases:
195 · You use --safe-recover.
197 · The temporary files needed to sort the keys would be more than
199 twice as big as when creating the key file directly. This is often
200 the case when you have large key values for CHAR, VARCHAR, or TEXT
201 columns, because the sort operation needs to store the complete key
202 values as it proceeds. If you have lots of temporary space and you
203 can force myisamchk to repair by sorting, you can use the
204 --sort-recover option.
205 Repairing through the key buffer takes much less disk space than using
207 sorting, but is also much slower.
208 If you want a faster repair, set the key_buffer_size and
210 sort_buffer_size variables to about 25% of your available memory. You
211 can set both variables to large values, because only one of them is
212 used at a time.
213 myisam_block_size is the size used for index blocks.
215 stats_method influences how NULL values are treated for index
217 statistics collection when the --analyze option is given. It acts like
218 the myisam_stats_method system variable. For more information, see the
219 description of myisam_stats_method in Section 5.1.4, “Server System
220 Variables”, and Section 7.4.7, “MyISAM Index Statistics Collection”.
221 ft_min_word_len and ft_max_word_len indicate the minimum and maximum
223 word length for FULLTEXT indexes. ft_stopword_file names the stopword
224 file. These need to be set under the following circumstances.
225 If you use myisamchk to perform an operation that modifies table
227 indexes (such as repair or analyze), the FULLTEXT indexes are rebuilt
228 using the default full-text parameter values for minimum and maximum
229 word length and the stopword file unless you specify otherwise. This
230 can result in queries failing.
231 The problem occurs because these parameters are known only by the
233 server. They are not stored in MyISAM index files. To avoid the problem
234 if you have modified the minimum or maximum word length or the stopword
235 file in the server, specify the same ft_min_word_len, ft_max_word_len,
236 and ft_stopword_file values to myisamchk that you use for mysqld. For
237 example, if you have set the minimum word length to 3, you can repair a
238 table with myisamchk like this:
239 shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI
241 To ensure that myisamchk and the server use the same values for
243 full-text parameters, you can place each one in both the [mysqld] and
244 [myisamchk] sections of an option file:
245 [mysqld]
247 ft_min_word_len=3
248 [myisamchk]
249 ft_min_word_len=3
250 An alternative to using myisamchk is to use the REPAIR TABLE, ANALYZE
252 TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements are performed
253 by the server, which knows the proper full-text parameter values to
254 use.
255
257 myisamchk supports the following options for table checking operations:
258 · --check, -c
260 Check the table for errors. This is the default operation if you
262 specify no option that selects an operation type explicitly.
263 · --check-only-changed, -C
265 Check only tables that have changed since the last check.
267 · --extend-check, -e
269 Check the table very thoroughly. This is quite slow if the table
271 has many indexes. This option should only be used in extreme cases.
272 Normally, myisamchk or myisamchk --medium-check should be able to
273 determine whether there are any errors in the table.
274 If you are using --extend-check and have plenty of memory, setting
276 the key_buffer_size variable to a large value helps the repair
277 operation run faster.
278 For a description of the output format, see the section called
280 “MYISAMCHK TABLE INFORMATION”.
281 · --fast, -F
283 Check only tables that haven´t been closed properly.
285 · --force, -f
287 Do a repair operation automatically if myisamchk finds any errors
289 in the table. The repair type is the same as that specified with
290 the --recover or -r option.
291 · --information, -i
293 Print informational statistics about the table that is checked.
295 · --medium-check, -m
297 Do a check that is faster than an --extend-check operation. This
299 finds only 99.99% of all errors, which should be good enough in
300 most cases.
301 · --read-only, -T
303 Do not mark the table as checked. This is useful if you use
305 myisamchk to check a table that is in use by some other application
306 that does not use locking, such as mysqld when run with external
307 locking disabled.
308 · --update-state, -U
310 Store information in the .MYI file to indicate when the table was
312 checked and whether the table crashed. This should be used to get
313 full benefit of the --check-only-changed option, but you shouldn´t
314 use this option if the mysqld server is using the table and you are
315 running it with external locking disabled.
316
318 myisamchk supports the following options for table repair operations
319 (operations performed when an option such as --recover or
320 --safe-recover is given):
321 · --backup, -B
323 Make a backup of the .MYD file as file_name-time.BAK
325 · --character-sets-dir=path
327 The directory where character sets are installed. See Section 9.5,
329 “Character Set Configuration”.
330 · --correct-checksum
332 Correct the checksum information for the table.
334 · --data-file-length=len, -D len
336 The maximum length of the data file (when re-creating data file
338 when it is “full”).
339 · --extend-check, -e
341 Do a repair that tries to recover every possible row from the data
343 file. Normally, this also finds a lot of garbage rows. Do not use
344 this option unless you are desperate.
345 For a description of the output format, see the section called
347 “MYISAMCHK TABLE INFORMATION”.
348 · --force, -f
350 Overwrite old intermediate files (files with names like
352 tbl_name.TMD) instead of aborting.
353 · --keys-used=val, -k val
355 For myisamchk, the option value is a bit-value that indicates which
357 indexes to update. Each binary bit of the option value corresponds
358 to a table index, where the first index is bit 0. An option value
359 of 0 disables updates to all indexes, which can be used to get
360 faster inserts. Deactivated indexes can be reactivated by using
361 myisamchk -r.
362 · --no-symlinks, -l
364 Do not follow symbolic links. Normally myisamchk repairs the table
366 that a symlink points to. This option does not exist as of MySQL
367 4.0 because versions from 4.0 on do not remove symlinks during
368 repair operations.
369 · --max-record-length=len
371 Skip rows larger than the given length if myisamchk cannot allocate
373 memory to hold them.
374 · --parallel-recover, -p
376 Use the same technique as -r and -n, but create all the keys in
378 parallel, using different threads. This is beta-quality code. Use
379 at your own risk!
380 · --quick, -q
382 Achieve a faster repair by modifying only the index file, not the
384 data file. You can specify this option twice to force myisamchk to
385 modify the original data file in case of duplicate keys.
386 · --recover, -r
388 Do a repair that can fix almost any problem except unique keys that
390 are not unique (which is an extremely unlikely error with MyISAM
391 tables). If you want to recover a table, this is the option to try
392 first. You should try --safe-recover only if myisamchk reports that
393 the table cannot be recovered using --recover. (In the unlikely
394 case that --recover fails, the data file remains intact.)
395 If you have lots of memory, you should increase the value of
397 sort_buffer_size.
398 · --safe-recover, -o
400 Do a repair using an old recovery method that reads through all
402 rows in order and updates all index trees based on the rows found.
403 This is an order of magnitude slower than --recover, but can handle
404 a couple of very unlikely cases that --recover cannot. This
405 recovery method also uses much less disk space than --recover.
406 Normally, you should repair first using --recover, and then with
407 --safe-recover only if --recover fails.
408 If you have lots of memory, you should increase the value of
410 key_buffer_size.
411 · --set-character-set=name
413 Change the character set used by the table indexes. This option was
415 replaced by --set-collation in MySQL 5.0.3.
416 · --set-collation=name
418 Specify the collation to use for sorting table indexes. The
420 character set name is implied by the first part of the collation
421 name.
422 · --sort-recover, -n
424 Force myisamchk to use sorting to resolve the keys even if the
426 temporary files would be very large.
427 · --tmpdir=path, -t path
429 The path of the directory to be used for storing temporary files.
431 If this is not set, myisamchk uses the value of the TMPDIR
432 environment variable. tmpdir can be set to a list of directory
433 paths that are used successively in round-robin fashion for
434 creating temporary files. The separator character between directory
435 names is the colon (“:”) on Unix and the semicolon (“;”) on
436 Windows, NetWare, and OS/2.
437 · --unpack, -u
439 Unpack a table that was packed with myisampack.
441
443 myisamchk supports the following options for actions other than table
444 checks and repairs:
445 · --analyze, -a
447 Analyze the distribution of key values. This improves join
449 performance by enabling the join optimizer to better choose the
450 order in which to join the tables and which indexes it should use.
451 To obtain information about the key distribution, use a myisamchk
452 --description --verbose tbl_name command or the SHOW INDEX FROM
453 tbl_name statement.
454 · --block-search=offset, -b offset
456 Find the record that a block at the given offset belongs to.
458 · --description, -d
460 Print some descriptive information about the table. Specifying the
462 --verbose option once or twice produces additional information. See
463 the section called “MYISAMCHK TABLE INFORMATION”.
464 · --set-auto-increment[=value], -A[value]
466 Force AUTO_INCREMENT numbering for new records to start at the
468 given value (or higher, if there are existing records with
469 AUTO_INCREMENT values this large). If value is not specified,
470 AUTO_INCREMENT numbers for new records begin with the largest value
471 currently in the table, plus one.
472 · --sort-index, -S
474 Sort the index tree blocks in high-low order. This optimizes seeks
476 and makes table scans that use indexes faster.
477 · --sort-records=N, -R N
479 Sort records according to a particular index. This makes your data
481 much more localized and may speed up range-based SELECT and ORDER
482 BY operations that use this index. (The first time you use this
483 option to sort a table, it may be very slow.) To determine a
484 table´s index numbers, use SHOW INDEX, which displays a table´s
485 indexes in the same order that myisamchk sees them. Indexes are
486 numbered beginning with 1.
487 If keys are not packed (PACK_KEYS=0), they have the same length, so
489 when myisamchk sorts and moves records, it just overwrites record
490 offsets in the index. If keys are packed (PACK_KEYS=1), myisamchk
491 must unpack key blocks first, then re-create indexes and pack the
492 key blocks again. (In this case, re-creating indexes is faster than
493 updating offsets for each index.)
494
496 To obtain a description of a MyISAM table or statistics about it, use
497 the commands shown here. The output from these commands is explained
498 later in this section.
499 · myisamchk -d tbl_name
501 Runs myisamchk in “describe mode” to produce a description of your
503 table. If you start the MySQL server with external locking
504 disabled, myisamchk may report an error for a table that is updated
505 while it runs. However, because myisamchk does not change the table
506 in describe mode, there is no risk of destroying data.
507 · myisamchk -dv tbl_name
509 Adding -v runs myisamchk in verbose mode so that it produces more
511 information about the table. Adding -v a second time produces even
512 more information.
513 · myisamchk -eis tbl_name
515 Shows only the most important information from a table. This
517 operation is slow because it must read the entire table.
518 · myisamchk -eiv tbl_name
520 This is like -eis, but tells you what is being done.
522 The tbl_name argument can be either the name of a MyISAM table or the
524 name of its index file, as described in myisamchk(1). Multiple tbl_name
525 arguments can be given.
526 Suppose that a table named person has the following structure. (The
528 MAX_ROWS table option is included so that in the example output from
529 myisamchk shown later, some values are smaller and fit the output
530 format more easily.)
531 CREATE TABLE person
533 (
534 id INT NOT NULL AUTO_INCREMENT,
535 last_name VARCHAR(20) NOT NULL,
536 first_name VARCHAR(20) NOT NULL,
537 birth DATE,
538 death DATE,
539 PRIMARY KEY (id),
540 INDEX (last_name, first_name),
541 INDEX (birth)
542 ) MAX_ROWS = 1000000;
543 Suppose also that the table has these data and index file sizes:
545 -rw-rw---- 1 mysql mysql 9347072 Aug 19 11:47 person.MYD
547 -rw-rw---- 1 mysql mysql 6066176 Aug 19 11:47 person.MYI
548 Example of myisamchk -dvv output:
550 MyISAM file: person
552 Record format: Packed
553 Character set: latin1_swedish_ci (8)
554 File-version: 1
555 Creation time: 2009-08-19 16:47:41
556 Recover time: 2009-08-19 16:47:56
557 Status: checked,analyzed,optimized keys
558 Auto increment key: 1 Last value: 306688
559 Data records: 306688 Deleted blocks: 0
560 Datafile parts: 306688 Deleted data: 0
561 Datafile pointer (bytes): 4 Keyfile pointer (bytes): 3
562 Datafile length: 9347072 Keyfile length: 6066176
563 Max datafile length: 4294967294 Max keyfile length: 17179868159
564 Recordlength: 54
565 table description:
566 Key Start Len Index Type Rec/key Root Blocksize
567 1 2 4 unique long 1 99328 1024
568 2 6 20 multip. varchar prefix 512 3563520 1024
569 27 20 varchar 512
570 3 48 3 multip. uint24 NULL 306688 6065152 1024
571 Field Start Length Nullpos Nullbit Type
572 1 1 1
573 2 2 4 no zeros
574 3 6 21 varchar
575 4 27 21 varchar
576 5 48 3 1 1 no zeros
577 6 51 3 1 2 no zeros
578 Explanations for the types of information myisamchk produces are given
580 here. “Keyfile” refers to the index file. “Record” and “row” are
581 synonymous, as are “field” and “column.”
582 The initial part of the table description contains these values:
584 · MyISAM file
586 Name of the MyISAM (index) file.
588 · Record format
590 The format used to store table rows. The preceding examples use
592 Fixed length. Other possible values are Compressed and Packed.
593 (Packed corresponds to what SHOW TABLE STATUS reports as Dynamic.)
594 · Chararacter set
596 The table default character set.
598 · File-version
600 Version of MyISAM format. Currently always 1.
602 · Creation time
604 When the data file was created.
606 · Recover time
608 When the index/data file was last reconstructed.
610 · Status
612 Table status flags. Possible values are crashed, open, changed,
614 analyzed, optimized keys, and sorted index pages.
615 · Auto increment key, Last value
617 The key number associated the table´s AUTO_INCREMENT column, and
619 the most recently generated value for this column. These fields do
620 not appear if there is no such column.
621 · Data records
623 The number of rows in the table.
625 · Deleted blocks
627 How many deleted blocks still have reserved space. You can optimize
629 your table to minimize this space. See Section 6.6.4, “MyISAM Table
630 Optimization”.
631 · Datafile parts
633 For dynamic-row format, this indicates how many data blocks there
635 are. For an optimized table without fragmented rows, this is the
636 same as Data records.
637 · Deleted data
639 How many bytes of unreclaimed deleted data there are. You can
641 optimize your table to minimize this space. See Section 6.6.4,
642 “MyISAM Table Optimization”.
643 · Datafile pointer
645 The size of the data file pointer, in bytes. It is usually 2, 3, 4,
647 or 5 bytes. Most tables manage with 2 bytes, but this cannot be
648 controlled from MySQL yet. For fixed tables, this is a row address.
649 For dynamic tables, this is a byte address.
650 · Keyfile pointer
652 The size of the index file pointer, in bytes. It is usually 1, 2,
654 or 3 bytes. Most tables manage with 2 bytes, but this is calculated
655 automatically by MySQL. It is always a block address.
656 · Max datafile length
658 How long the table data file can become, in bytes.
660 · Max keyfile length
662 How long the table index file can become, in bytes.
664 · Recordlength
666 How much space each row takes, in bytes.
668 The table description part of the output includes a list of all keys in
670 the table. For each key, myisamchk displays some low-level information:
671 · Key
673 This key´s number. This value is shown only for the first column of
675 the key. If this value is missing, the line corresponds to the
676 second or later column of a multiple-column key. For the table
677 shown in the example, there are two table description lines for the
678 second index. This indicates that it is a multiple-part index with
679 two parts.
680 · Start
682 Where in the row this portion of the index starts.
684 · Len
686 How long this portion of the index is. For packed numbers, this
688 should always be the full length of the column. For strings, it may
689 be shorter than the full length of the indexed column, because you
690 can index a prefix of a string column. The total length of a
691 multiple-part key is the sum of the Len values for all key parts.
692 · Index
694 Whether a key value can exist multiple times in the index. Possible
696 values are unique or multip. (multiple).
697 · Type
699 What data type this portion of the index has. This is a MyISAM data
701 type with the possible values packed, stripped, or empty.
702 · Root
704 Address of the root index block.
706 · Blocksize
708 The size of each index block. By default this is 1024, but the
710 value may be changed at compile time when MySQL is built from
711 source.
712 · Rec/key
714 This is a statistical value used by the optimizer. It tells how
716 many rows there are per value for this index. A unique index always
717 has a value of 1. This may be updated after a table is loaded (or
718 greatly changed) with myisamchk -a. If this is not updated at all,
719 a default value of 30 is given.
720 The last part of the output provides information about each column:
722 · Field
724 The column number.
726 · Start
728 The byte position of the column within table rows.
730 · Length
732 The length of the column in bytes.
734 · Nullpos, Nullbit
736 For columns that can be NULL, MyISAM stores NULL values as a flag
738 in a byte. Depending on how many nullable columns there are, there
739 can be one or more bytes used for this purpose. The Nullpos and
740 Nullbit values, if nonempty, indicate which byte and bit contains
741 that flag indicating whether the column is NULL.
742 The position and number of bytes used to store NULL flags is shown
744 in the line for field 1. This is why there are six Field lines for
745 the person table even though it has only five columns.
746 · Type
748 The data type. The value may contain any of the following
750 descriptors:
751 · constant
753 All rows have the same value.
755 · no endspace
757 Do not store endspace.
759 · no endspace, not_always
761 Do not store endspace and do not do endspace compression for
763 all values.
764 · no endspace, no empty
766 Do not store endspace. Do not store empty values.
768 · table-lookup
770 The column was converted to an ENUM.
772 · zerofill(N)
774 The most significant N bytes in the value are always 0 and are
776 not stored.
777 · no zeros
779 Do not store zeros.
781 · always zero
783 Zero values are stored using one bit.
785 · Huff tree
787 The number of the Huffman tree associated with the column.
789 · Bits
791 The number of bits used in the Huffman tree.
793 The Huff tree and Bits fields are displayed if the table has been
795 compressed with myisampack. See myisampack(1), for an example of this
796 information.
797 Example of myisamchk -eiv output:
799 Checking MyISAM file: person
801 Data records: 306688 Deleted blocks: 0
802 - check file-size
803 - check record delete-chain
804 No recordlinks
805 - check key delete-chain
806 block_size 1024:
807 - check index reference
808 - check data record references index: 1
809 Key: 1: Keyblocks used: 98% Packed: 0% Max levels: 3
810 - check data record references index: 2
811 Key: 2: Keyblocks used: 99% Packed: 97% Max levels: 3
812 - check data record references index: 3
813 Key: 3: Keyblocks used: 98% Packed: -14% Max levels: 3
814 Total: Keyblocks used: 98% Packed: 89%
815 - check records and index references
816 *** LOTS OF ROW NUMBERS DELETED ***
817 Records: 306688 M.recordlength: 25 Packed: 83%
818 Recordspace used: 97% Empty space: 2% Blocks/Record: 1.00
819 Record blocks: 306688 Delete blocks: 0
820 Record data: 7934464 Deleted data: 0
821 Lost space: 256512 Linkdata: 1156096
822 User time 43.08, System time 1.68
823 Maximum resident set size 0, Integral resident set size 0
824 Non-physical pagefaults 0, Physical pagefaults 0, Swaps 0
825 Blocks in 0 out 7, Messages in 0 out 0, Signals 0
826 Voluntary context switches 0, Involuntary context switches 0
827 Maximum memory usage: 1046926 bytes (1023k)
828 myisamchk -eiv output includes the following information:
830 · Data records
832 The number of rows in the table.
834 · Deleted blocks
836 How many deleted blocks still have reserved space. You can optimize
838 your table to minimize this space. See Section 6.6.4, “MyISAM Table
839 Optimization”.
840 · Key
842 The key number.
844 · Keyblocks used
846 What percentage of the keyblocks are used. When a table has just
848 been reorganized with myisamchk, the values are very high (very
849 near theoretical maximum).
850 · Packed
852 MySQL tries to pack key values that have a common suffix. This can
854 only be used for indexes on CHAR and VARCHAR columns. For long
855 indexed strings that have similar leftmost parts, this can
856 significantly reduce the space used. In the preceding example, the
857 second key is 40 bytes long and a 97% reduction in space is
858 achieved.
859 · Max levels
861 How deep the B-tree for this key is. Large tables with long key
863 values get high values.
864 · Records
866 How many rows are in the table.
868 · M.recordlength
870 The average row length. This is the exact row length for tables
872 with fixed-length rows, because all rows have the same length.
873 · Packed
875 MySQL strips spaces from the end of strings. The Packed value
877 indicates the percentage of savings achieved by doing this.
878 · Recordspace used
880 What percentage of the data file is used.
882 · Empty space
884 What percentage of the data file is unused.
886 · Blocks/Record
888 Average number of blocks per row (that is, how many links a
890 fragmented row is composed of). This is always 1.0 for fixed-format
891 tables. This value should stay as close to 1.0 as possible. If it
892 gets too large, you can reorganize the table. See Section 6.6.4,
893 “MyISAM Table Optimization”.
894 · Recordblocks
896 How many blocks (links) are used. For fixed-format tables, this is
898 the same as the number of rows.
899 · Deleteblocks
901 How many blocks (links) are deleted.
903 · Recorddata
905 How many bytes in the data file are used.
907 · Deleted data
909 How many bytes in the data file are deleted (unused).
911 · Lost space
913 If a row is updated to a shorter length, some space is lost. This
915 is the sum of all such losses, in bytes.
916 · Linkdata
918 When the dynamic table format is used, row fragments are linked
920 with pointers (4 to 7 bytes each). Linkdata is the sum of the
921 amount of storage used by all such pointers.
922
924 Memory allocation is important when you run myisamchk. myisamchk uses
925 no more memory than its memory-related variables are set to. If you are
926 going to use myisamchk on very large tables, you should first decide
927 how much memory you want it to use. The default is to use only about
928 3MB to perform repairs. By using larger values, you can get myisamchk
929 to operate faster. For example, if you have more than 32MB RAM, you
930 could use options such as these (in addition to any other options you
931 might specify):
932 shell> myisamchk --sort_buffer_size=16M \
934 --key_buffer_size=16M \
935 --read_buffer_size=1M \
936 --write_buffer_size=1M ...
937 Using --sort_buffer_size=16M should probably be enough for most cases.
939 Be aware that myisamchk uses temporary files in TMPDIR. If TMPDIR
941 points to a memory file system, out of memory errors can easily occur.
942 If this happens, run myisamchk with the --tmpdir=path option to specify
943 a directory located on a file system that has more space.
944 When performing repair operations, myisamchk also needs a lot of disk
946 space:
947 · Twice the size of the data file (the original file and a copy).
949 This space is not needed if you do a repair with --quick; in this
950 case, only the index file is re-created. This space must be
951 available on the same file system as the original data file, as the
952 copy is created in the same directory as the original.
953 · Space for the new index file that replaces the old one. The old
955 index file is truncated at the start of the repair operation, so
956 you usually ignore this space. This space must be available on the
957 same file system as the original data file.
958 · When using --recover or --sort-recover (but not when using
960 --safe-recover), you need space on disk for sorting. This space is
961 allocated in the temporary directory (specified by TMPDIR or
962 --tmpdir=path). The following formula yields the amount of space
963 required:
964 (largest_key + row_pointer_length) × number_of_rows × 2
966 You can check the length of the keys and the row_pointer_length
968 with myisamchk -dv tbl_name (see the section called “MYISAMCHK
969 TABLE INFORMATION”). The row_pointer_length and number_of_rows
970 values are the Datafile pointer and Data records values in the
971 table description. To determine the largest_key value, check the
972 Key lines in the table description. The Len column indicates the
973 number of bytes for each key part. For a multiple-column index, the
974 key size is the sum of the Len values for all key parts.
975 If you have a problem with disk space during repair, you can try
977 --safe-recover instead of --recover.
978
980 Copyright 2007-2008 MySQL AB, 2008-2010 Sun Microsystems, Inc.
981 This documentation is free software; you can redistribute it and/or
983 modify it only under the terms of the GNU General Public License as
984 published by the Free Software Foundation; version 2 of the License.
985 This documentation is distributed in the hope that it will be useful,
987 but WITHOUT ANY WARRANTY; without even the implied warranty of
988 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
989 General Public License for more details.
990 You should have received a copy of the GNU General Public License along
992 with the program; if not, write to the Free Software Foundation, Inc.,
993 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see
994 http://www.gnu.org/licenses/.
995
998 For more information, please refer to the MySQL Reference Manual, which
999 may already be installed locally and which is also available online at
1000 http://dev.mysql.com/doc/.
1001
1003 Sun Microsystems, Inc. (http://www.mysql.com/).
1004MySQL 5.1 04/06/2010 MYISAMCHK(1)