PostgreSQL

Solution

Logical decoding / a publication (Debezium or native), not polling updated_at. Monitor slot lag and disk. A slot nobody consumes is how the primary fills the disk.

Solution

EXPLAIN (ANALYZE, BUFFERS). Name seq scan vs index, then decide. Adding an index without a plan is cargo cult.

Solution

Bloat. Dead tuples, delayed VACUUM, long transactions. Autovacuum is an SLO. “We will warehouse it” does not fix the primary.

Solution

Not for BI. Replica or CDC copy. A federated scan of prod is an outage. Say this even if they did not ask.

Solution

Postgres unique allows multiple NULLs (until NULLS NOT DISTINCT). Warehouse dialects differ. CDC + MERGE on a nullable key silently drops or dupes. Name the constraint.

Solution

You lose the WAL you have not consumed; a new slot starts from now (or a snapshot). Disk may recover. Never drop a slot to “free disk” without a re-snapshot plan. Also check a forgotten unused slot.

Solution

pg_stat_statements / EXPLAIN ANALYZE to show the seq scan. Then a replica or a warehouse mart — not a bigger primary. Federation of OLTP is how you take checkout down.

Solution

Dead tuples need VACUUM; file shrink needs VACUUM FULL or a rewrite (and a lock). Bloat from updates without fillfactor/autovacuum tuning. Measure n_dead_tup before buying disk.

Solution

Default UNIQUE allows multiple NULLs because NULL ≠ NULL. If “one empty email” is the rule, use NULLS NOT DISTINCT (PG 15+) or a sentinel. This bites MERGE/CDC keys too.

Solution

Small DBs, no delete capture needed, or you cannot get a slot. CDC is for ongoing deltas and deletes. A dump is a snapshot grain — say that in the mart.

Solution

A failed concurrent build leaves an invalid index that still costs writes. DROP INDEX and retry. Do not leave INVALID indexes in prod.