Explain MySQL's query cache and its optimization.

Query cache stores SELECT statement results in memory for faster retrieval.

Configuration:
query_cache_type = 1
query_cache_size = 256M

Optimization tips:
• Use identical queries
• Avoid non-deterministic functions
• Monitor cache hit ratio
• Consider disabling for write-heavy workloads

Example:
SHOW STATUS LIKE 'Qcache%';
-- Shows cache statistics and hit ratio