Comment by Tostino
9 hours ago
Clustered indexes aren't just about write amplification. They also reduce the reads needed to get the data. Sometimes by quite a bit.
9 hours ago
Clustered indexes aren't just about write amplification. They also reduce the reads needed to get the data. Sometimes by quite a bit.
That's true for seeks into the clustered (primary) index because that index includes all fields, so you don't need to "jump" to the heap to get them.
However, seeking into a secondary index, and then reading a column not included in that index incurs an additional index seek (into the clustered index), which may be somewhat slower than what would happen in a heap-based table.
So there are pros and cons, as usual...