> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/server/server-usage/storage-engines/myisam-storage-engine/myisam-index-storage-space.md).

# MyISAM Index Storage Space

Regular [MyISAM](/docs/server/server-usage/storage-engines/myisam-storage-engine.md) tables make use of [B-tree indexes](/docs/server/ha-and-performance/optimization-and-tuning/optimization-and-indexes/storage-engine-index-types.md#b-tree-indexes).

String indexes are space-compressed, which reduces the size of [VARCHARs](/docs/server/reference/data-types/string-data-types/varchar.md) that don't use the full length, or a string that has trailing spaces. String indexes also make use of prefix-compression, where strings with identical prefixes are compressed.

Numeric indexes can also be prefix-compressed if the [PACK\_KEYS=1](/docs/server/server-usage/tables/create-table.md#table-options) option is used. Regardless, the high byte is always stored first, which allows a reduced index size.

In the worst case, with no strings being space-compressed, the total index storage space are (index\_length+4)/0.67 per index.

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