8.7 Optimizing for MEMORY Tables
MEMORY tables for noncritical data that is accessed often, and is read-only or rarely updated. Benchmark your application against equivalent
MyISAM tables under a realistic workload, to confirm that any additional performance is worth the risk of losing data, or the overhead of copying data from a disk-based table at application start.
For best performance with
MEMORY tables, examine the kinds of queries against each table, and specify the type to use for each associated index, either a B-tree index or a hash index. On the
CREATE INDEX statement, use the clause
USING BTREE or
USING HASH. B-tree indexes are fast for queries that do greater-than or less-than comparisons through operators such as
BETWEEN. Hash indexes are only fast for queries that look up single values through the
= operator, or a restricted set of values through the
IN operator. For why
USING BTREE is often a better choice than the default
USING HASH, see Section 18.104.22.168, “Avoiding Full Table Scans”. For implementation details of the different types of
MEMORY indexes, see Section 8.3.8, “Comparison of B-Tree and Hash Indexes”.