10. Choosing Storage Structures and Secondary Indexes : Hash Storage Structure : Hash Troubleshooting
 
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Hash Troubleshooting
The following are problems encountered with hash storage structure, and their solutions:
Problem
Solution
Pattern matching and range scans used; performance slow.
Use ISAM or B-tree instead.
Partial key of multi-column key used; performance slow.
Use ISAM or B-tree instead.
Overflow pages occur in table after adding rows.
Remodify.
Overflow pages occur in newly modified table.
If key is repetitive, this is normal but undesirable. If key is unique, hashing algorithm does not distribute data well; try increasing minpages. If column is a character column that only partially varies (for example, AAAAA1 AAAAA2), consider using ISAM instead.