Hash access (ACCESSTYPE='H', 'HN', or 'MH')
(deprecated)
The ACCESSTYPE column in the plan table has a value of 'H', 'HN', or 'MH', when the table
being accessed is organized by hash, and hash access is used to access the data.
Hash-organized table spaces are deprecated and will be unsupported in the future.
FL 504 Hash-organized tables are deprecated, and applications that run at APPLCOMPAT levelV12R1M504 or higher cannot create hash-organized tables or alter existing tables to use hash-organization. Existing hash-organized tables remain supported, but they will be unsupported in the future.
Hash access is efficient for
queries that use equal predicates to access a single row on a table.
Hash access also reduces CPU load. However the use of hash access
requires additional storage space for maintenance of the hash space.
If a table is organized by hash, index clustering is unavailable on
that table.
When a hash access path is selected for a parallel group, parallelism is not selected for that parallel group, however Db2 might select parallelism for other parallel groups in the query.
When star join is enabled, Db2 does
not use hash access for either the fact or dimension tables when a
query contains a qualified star join.