The discussion in this section describes how to use
.MYD). If you are using
ISAM tables (extensions
should use isamchk instead; the concepts are
Symptoms of corrupted tables include queries that abort unexpectedly and observable errors such as these:
is locked against change
Can't find file
Unexpected end of file
Record file is crashed
nnn from table handler
To get more information about the error, run
nnn is the error number. The
following example shows how to use perror to
find the meanings for the most common error numbers that
indicate a problem with a table:
perror 126 127 132 134 135 136 141 144 145MySQL error code 126 = Index file is crashed MySQL error code 127 = Record-file is crashed MySQL error code 132 = Old database file MySQL error code 134 = Record was already deleted (or record file crashed) MySQL error code 135 = No more room in record file MySQL error code 136 = No more room in index file MySQL error code 141 = Duplicate unique key or constraint on write or update MySQL error code 144 = Table is crashed and last repair failed MySQL error code 145 = Table was marked as crashed and should be repaired
Note that error 135 (no more room in record file) and error 136
(no more room in index file) are not errors that can be fixed by
a simple repair. In this case, you must use
ALTER TABLE to increase the
AVG_ROW_LENGTH table option values:
If you do not know the current table option values, use
SHOW CREATE TABLE.
For the other errors, you must repair your tables. myisamchk can usually detect and fix most problems that occur.
The repair process involves up to four stages, described here. Before you begin, you should change location to the database directory and check the permissions of the table files. On Unix, make sure that they are readable by the user that mysqld runs as (and to you, because you need to access the files you are checking). If it turns out you need to modify files, they must also be writable by you.
This section is for the cases where a table check fails (such as
those described in Section 6.6.2, “How to Check
MyISAM Tables for Errors”), or you want
to use the extended features that myisamchk
The options that you can use for table maintenance with myisamchk and isamchk are described in Section 4.6.2, “myisamchk — MyISAM Table-Maintenance Utility”. myisamchk also has variables that you can set to control memory allocation that may improve performance. See Section 126.96.36.199, “myisamchk Memory Usage”.
If you are going to repair a table from the command line, you must first stop the mysqld server. Note that when you do mysqladmin shutdown on a remote server, the mysqld server is still available for a while after mysqladmin returns, until all statement-processing has stopped and all index changes have been flushed to disk.
Stage 1: Checking your tables
You have to repair only those tables for which myisamchk announces an error. For such tables, proceed to Stage 2.
If you get unexpected errors when checking (such as
of memory errors), or if myisamchk
crashes, go to Stage 3.
Stage 2: Easy safe repair
First, try myisamchk -r -q
-q means “quick recovery mode”). This
attempts to repair the index file without touching the data
file. If the data file contains everything that it should and
the delete links point at the correct locations within the data
file, this should work, and the table is fixed. Start repairing
the next table. Otherwise, use the following procedure:
Make a backup of the data file before continuing.
Use myisamchk -r
-r means “recovery mode”).
This removes incorrect rows and deleted rows from the data
file and reconstructs the index file.
If the preceding step fails, use myisamchk
tbl_name. Safe recovery
mode uses an old recovery method that handles a few cases
that regular recovery mode does not (but is slower).
If you get unexpected errors when repairing (such as
out of memory errors), or if
myisamchk crashes, go to Stage 3.
Stage 3: Difficult repair
You should reach this stage only if the first 16KB block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it is necessary to create a new index file. Do so as follows:
Move the data file to a safe place.
Use the table description file to create new (empty) data and index files:
If your version of MySQL does not have
TRUNCATE TABLE, use
Copy the old data file back onto the newly created data file. (Do not just move the old file back onto the new file. You want to retain a copy in case something goes wrong.)
If you are using replication, you should stop it prior to performing the above procedure, since it involves file system operations, and these are not logged by MySQL.
Go back to Stage 2. myisamchk -r -q should work. (This should not be an endless loop.)
As of MySQL 4.0.2, you can also use the
statement, which performs the whole procedure automatically.
There is also no possibility of unwanted interaction between a
utility and the server, because the server does all the work
when you use
REPAIR TABLE. See
Section 188.8.131.52, “
REPAIR TABLE Syntax”.
Stage 4: Very difficult repair
You should reach this stage only if the
.frm description file has also crashed.
That should never happen, because the description file is not
changed after the table is created:
Restore the description file from a backup and go back to Stage 3. You can also restore the index file and go back to Stage 2. In the latter case, you should start with myisamchk -r.
If you do not have a backup but know exactly how the table
was created, create a copy of the table in another database.
Remove the new data file, and then move the
.frm description and
.MYI index files from the other
database to your crashed database. This gives you new
description and index files, but leaves the
.MYD data file alone. Go back to Stage
2 and attempt to reconstruct the index file.