core practice · coding problem
Secondary index write cost
Table with 3 secondary indexes. One INSERT touches how many index structures?
The mechanism
A secondary index is an extra sorted lookup that maps a non-primary-key value (like email) back to the rows that match. Reads on that value get fast; writes get a little slower because the index also has to update. Every index is a tradeoff — only add the ones queries actually need.
Expected evidence
Primary + 3 secondaries = 4 writes (plus WAL).
Try this drill in the practice workspace →
Hints when you need them
- Each index is another B-tree insert.
- Indexes speed reads, tax writes.