What's the relation between:
innodb_buffer_pool_size and query_cache_*
Both are use for caching queries but what's the difference? Can I use both?
Buffer pool is for caching retrieved table and index data in memory, query cache just caches the parsed mysql queries. The former is much larger and usually far more important. Sure you can use both.
innodb_buffer_pool_size = caches the tables for better response times
query_cache = for remembering queries to get them faster the next time you execute the same query