Problem: Disk Latency

• Typical HDD performance (non-SSD):

• Sequential ~100MB/sec (1M rows @ 100B). Great!

• Random access ~100 IO/sec (100 rows/sec). That's bad :-(

• Possible solutions:

• DB block cache -> fails when working set > RAM.

• LOTS of disks -> works, but expensive.

• Data locality -> clustered indexes.