SpirirHost Support Centre: MySQL Reference Manual p.247

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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 4: Database Administration 247 the space used. In the third example above, the 4th key is 10 characters long and a 60% reduction in space is achieved. Max levels How deep the B-tree for this key is. Large tables with long keys get high values. Records How many rows are in the table. M.recordlength The average record length. For tables with xed-length records, this is the exact record length. Packed MySQL strips spaces from the end of strings. The Packed value indicates the percentage of savings achieved by doing this. Recordspace used What percentage of the datale is used. Empty space What percentage of the datale is unused. Blocks/Record Average number of blocks per record (that is, how many links a frag- mented record is composed of). This is always 1.0 for xed-format tables. This value should stay as close to 1.0 as possible. If it gets too big, you can reorganise the table with myisamchk. See Section 4.4.6.10 [Optimisation], page 241. Recordblocks How many blocks (links) are used. For xed format, this is the same as the number of records. Deleteblocks How many blocks (links) are deleted. Recorddata How many bytes in the datale are used. Deleted data How many bytes in the datale are deleted (unused). Lost space If a record is updated to a shorter length, some space is lost. This is the sum of all such losses, in bytes. Linkdata When the dynamic table format is used, record fragments are linked with pointers (4 to 7 bytes each). Linkdata is the sum of the amount of storage used by all such pointers. If a table has been compressed with myisampack, myisamchk -d prints additional informa- tion about each table column. See Section 4.7.4 [myisampack], page 279, for an example of this information and a description of what it means. 4.5 Database Administration Language Reference 4.5.1 OPTIMIZE TABLE Syntax OPTIMIZE TABLE tbl_name[,tbl_name]... OPTIMIZE TABLE should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have VARCHAR, BLOB, or TEXT columns). Deleted records are maintained in a linked list and subsequent INSERT operations reuse old record positions. You can use OPTIMIZE TABLE to reclaim the unused space and to defragment the datale.

MySQL Reference Manual

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