The index exists but EXPLAIN shows a sequential scan

You

The index exists but EXPLAIN shows a sequential scan.

ChatGPT

Usually one of three things: the query returns a large fraction of the table so the scan really is cheaper, the types do not match so the index is not applicable, or statistics are stale. ANALYZE the table first, then compare with SET enable_seqscan = off to see what the planner thinks the index would cost.

Tool steps: 3 (reasoning summary, call to python, execution output)

reasoning summary

Checked the query plan, then compared index options.

call to python

rows = run_sql("EXPLAIN (ANALYZE) SELECT ...")
print(rows[:3])

execution output

Seq Scan on events  (cost=0.00..812431.00 rows=41203122 width=16)
  Rows Removed by Filter: 38996878
Planning Time: 0.214 ms
Execution Time: 11842.663 ms

You

Users see their own edits disappear after saving. Replica lag?

ChatGPT

Almost certainly. Route reads that follow a write by the same user to the primary for a short window, or track the write LSN in the session and wait for the replica to reach it. The general fix is read-your-writes consistency, not lower lag.