ASA SQL User's Guide
Query Optimization and Execution
Indexes
Adaptive Server Anywhere supports two types of index, and automatically chooses between them depending on the declared width of the indexed columns. For a total column width that is less than 10 bytes, Adaptive Server Anywhere uses a B-tree index that contains an order-preserving encoding, or hash value, that represents the indexed data. Hash B-tree indexes are also used when the index key length is longer than one-eighth of the page size for the database or 256 bytes (whichever is lower). For data values whose combined declared length is between these two bounds, Adaptive Server Anywhere uses a compressed B-tree index that stores each key in a compressed form.
Indexes can be stored as either clustered or unclustered. Clustered indexes may assist performance, but only one index on a table can be clustered.
Hash B-tree indexes
Compressed B-tree indexes
Recommended page sizes