Deep Dive
Why an Index Only Scan Still Read the Heap
The plan said Index Only Scan, the buffers said the heap was read anyway, and the win never arrived. Index only is conditional on the visibility map, and…
Deep Dive
Vacuum, Dead Tuples and the Wraparound Shutdown Nobody Plans For
MVCC gives every transaction an id and keeps old row versions until vacuum says they are dead to everyone. If vacuum falls behind for long enough, the id…
Error Autopsy
relation does not exist for a Table That Is Definitely There
The query fails with relation does not exist while the table sits in the schema browser a click away. The table never moved.
Bug Hunt
The Slow Query That Ran in Four Milliseconds Under EXPLAIN
In production the query took nine hundred milliseconds. Under EXPLAIN it ran in four. The difference was the plan: production ran a cached generic plan…
Error Autopsy
Postgres 40001: Why Retrying the Transaction Is Correct
ERROR 40001 looks like a crash and feels like a bug. It is neither. It is the serializable isolation level doing its job, and the only correct client…
Performance
The Index That Made Inserts Four Times Slower
Every index is a second write. On an insert heavy table, nine well meaning indexes turned a fast append into a small transaction against ten data…
Code Review
Reviewing a Migration on a 400 Million Row Table
A migration that is instant on a thousand row table can lock a production table for minutes at scale. Review for locking, backfill strategy and rollback…
Performance
PgBouncer Transaction Mode Broke Every Prepared Statement
After switching the pooler to transaction mode, the app started failing with 'prepared statement does not exist' at random.
PostgreSQL
Autovacuum Is Running and Your Table Is Still Bloating
Dead tuples that never get reclaimed, a table twice the size of its data, and queries getting slower every week. Here is what blocks vacuum and how to see it.
PostgreSQL
Postgres deadlock detected: Fix the Lock Order
Two transactions each hold what the other wants. Here is how to read the deadlock report, find both statements, and restructure so it cannot happen again.
PostgreSQL
Why Your Index Is Not Used: Reading EXPLAIN ANALYZE
You added the index and the query is still slow. Here is how to read a Postgres query plan properly and find the row estimate error causing it.
Bug Hunt
How a Timezone Bug Silently Corrupted Three Months of Analytics
The dashboard looked right. The numbers were wrong by a few percent every day, and the reason was one implicit conversion in a reporting query.