Dyntex.net Support Centre: MySQL Reference Manual p.497

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 7: MySQL Table Types 497 If the repair fails, retry once more with the old repair option method (write row by row without sorting) which should be able to repair any type of error with little disk requirements.. If the recover wouldn't be able to recover all rows from a previous completed statement and you didn't specify FORCE as an option to myisam-recover, then the automatic repair will abort with an error message in the error le: Error: Couldn't repair table: test.g00pages If you in this case had used the FORCE option you would instead have got a warning in the error le: Warning: Found 344 of 354 rows when repairing ./test/g00pages Note that if you run automatic recover with the BACKUP option, you should have a cron script that automatically moves le with names like `tablename-datetime.BAK' from the database directories to a backup media. See Section 4.1.1 [Command-line options], page 181. 7.1.1 Space Needed for Keys MySQL can support dierent index types, but the normal type is ISAM or MyISAM. These use a B-tree index, and you can roughly calculate the size for the index le as (key_ length+4)/0.67, summed over all keys. (This is for the worst case when all keys are inserted in sorted order and we don't have any compressed keys.) String indexes are space compressed. If the rst index part is a string, it will also be prex compressed. Space compression makes the index le smaller than the above gures if the string column has a lot of trailing space or is a VARCHAR column that is not always used to the full length. Prex compression is used on keys that start with a string. Prex compression helps if there are many strings with an identical prex. In MyISAM tables, you can also prex compress numbers by specifying PACK_KEYS=1 when you create the table. This helps when you have many integer keys that have an identical prex when the numbers are stored high-byte rst. 7.1.2 MyISAM Table Formats MyISAM supports 3 dierent table types. Two of them are chosen automatically depending on the type of columns you are using. The third, compressed tables, can only be created with the myisampack tool. When you CREATE or ALTER a table you can for tables that doesn't have BLOBs force the table format to DYNAMIC or FIXED with the ROW_FORMAT=# table option. In the future you will be able to compress/decompress tables by specifying ROW_FORMAT=compressed | default to ALTER TABLE. See Section 6.5.3 [CREATE TABLE], page 469.

MySQL Reference Manual

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