Core conceptsintermediate
Checkpoint
A point at which PostgreSQL flushes dirty buffers to disk and records a WAL position, bounding how much WAL must be replayed after a crash.
What this means
Every so often Postgres stops to flush all the changes sitting in memory out to the real table files, and writes a "you are here" mark into the WAL. That mark is where crash recovery starts replaying from, so checkpoints put a ceiling on how much log has to be re-applied after a crash.
Why it matters operationally
Checkpoint timing trades recovery time against write spikes; tuning it is central to smoothing I/O on write-heavy systems.
Related errors
Where it lives in the source
src/backend/postmaster/checkpointer.c