Database Administrator Guide > Database Administrator Guide > Choosing Storage Structures and Secondary Indexes > ISAM or B-tree? > When to Choose ISAM over B-tree
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When to Choose ISAM over B-tree
The ISAM storage structure has the following advantages over B-tree:
• ISAM is better for static tables (ones that have no updates on key fields, appends, or deletes) where no overflow chains exist.
• ISAM requires fewer disk operations to visit a data page than B-tree, because B-tree has an additional leaf level.
• ISAM is much better for small tables. B-tree requires a minimum of a free list header page, a root page, a leaf page, and a data page. ISAM requires only a root and a data page. B-trees for less than 10 to 15 pages are better stored as ISAM. B-tree tables take up more space than do ISAM tables; this is most noticeable when tables are small.
• ISAM requires no locking in the index pages, while B-tree incurs index locking; therefore concurrent performance in the index of a B-tree is not as good as concurrent performance in the index pages of an ISAM. However, concurrent usage in B-tree data pages is better than concurrent usage in ISAM data pages if the ISAM table has long overflow chains.
Last modified date: 08/14/2024