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MySQL 5.7 Reference Manual
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16.2.1 MyISAM Startup Options

The following options to mysqld can be used to change the behavior of MyISAM tables. For additional information, see Section 6.1.3, “Server Command Options”.

Table 16.3 MyISAM Option/Variable Reference

NameCmd-LineOption FileSystem VarStatus VarVar ScopeDynamic
bulk_insert_buffer_sizeYesYesYes BothYes
concurrent_insertYesYesYes GlobalYes
delay-key-writeYesYes  GlobalYes
- Variable: delay_key_write  Yes GlobalYes
have_rtree_keys  Yes GlobalNo
key_buffer_sizeYesYesYes GlobalYes
log-isamYesYes    
myisam-block-sizeYesYes    
myisam_data_pointer_sizeYesYesYes GlobalYes
myisam_max_sort_file_sizeYesYesYes GlobalYes
myisam_mmap_sizeYesYesYes GlobalNo
myisam-recover-optionsYesYes    
- Variable: myisam_recover_options      
myisam_recover_options  Yes GlobalNo
myisam_repair_threadsYesYesYes BothYes
myisam_sort_buffer_sizeYesYesYes BothYes
myisam_stats_methodYesYesYes BothYes
myisam_use_mmapYesYesYes GlobalYes
skip-concurrent-insertYesYes    
- Variable: concurrent_insert      
tmp_table_sizeYesYesYes BothYes

  • --myisam-recover-options=mode

    Set the mode for automatic recovery of crashed MyISAM tables.

  • --delay-key-write=ALL

    Don't flush key buffers between writes for any MyISAM table.

    Note

    If you do this, you should not access MyISAM tables from another program (such as from another MySQL server or with myisamchk) when the tables are in use. Doing so risks index corruption. Using --external-locking does not eliminate this risk.

The following system variables affect the behavior of MyISAM tables. For additional information, see Section 6.1.4, “Server System Variables”.

Automatic recovery is activated if you start mysqld with the --myisam-recover-options option. In this case, when the server opens a MyISAM table, it checks whether the table is marked as crashed or whether the open count variable for the table is not 0 and you are running the server with external locking disabled. If either of these conditions is true, the following happens:

  • The server checks the table for errors.

  • If the server finds an error, it tries to do a fast table repair (with sorting and without re-creating the data file).

  • If the repair fails because of an error in the data file (for example, a duplicate-key error), the server tries again, this time re-creating the data file.

  • If the repair still fails, the server tries once more with the old repair option method (write row by row without sorting). This method should be able to repair any type of error and has low disk space requirements.

If the recovery wouldn't be able to recover all rows from previously completed statements and you didn't specify FORCE in the value of the --myisam-recover-options option, automatic repair aborts with an error message in the error log:

Error: Couldn't repair table: test.g00pages

If you specify FORCE, a warning like this is written instead:

Warning: Found 344 of 354 rows when repairing ./test/g00pages

If the automatic recovery value includes BACKUP, the recovery process creates files with names of the form tbl_name-datetime.BAK. You should have a cron script that automatically moves these files from the database directories to backup media.


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