I have a MySQL table with 20,000,000 rows and also a MySQL memory table with 10,000,000 rows.
Each row is 6 columns, 5 of which are VARCHAR(45).
Both tables have multi-column indexes on the exact columns which are being selected with WHERE clause.
Both tables are SLOW (even the memory table) taking about 10 seconds per SELECT. I don't know how to fix this. The server is a dedicated Dual-Quad-Core with 12GB of RAM.
How can I speed this up?