Explain the difference between creating an index before vs after bulk loading data.

Creating index BEFORE bulk load: each INSERT also updates the index. For 10M rows: 10M index insertions (individual B-Tree inserts). Much slower overall. Creating index AFTER bulk load: 1) Load all rows (INSERT or COPY) without index — fast sequential writes. 2) Then CREATE INDEX CONCURRENTLY — reads all rows once, builds sorted index. Total: load time + one full table scan. Orders of magnitude fa