Partition pruning (plan-time, init-time, exec-time)
Simple terms
'Pruning happens at plan time' is about a third of the story. Postgres can rule out a partition at three separate moments: while planning, when the value is a literal constant; at executor startup, when it is a parameter that only becomes known then; and row by row inside a join. Each looks different in EXPLAIN, which is how a partition can appear in the plan and never actually run. And all of it stops silently if you filter on a column that isn't the partition key.
You might be asked
A query against a table partitioned by month only touches one month, yet someone tells you 'partition pruning happens at plan time.' Push past that: name the THREE distinct moments PostgreSQL can prune a partition, show how each one looks different in EXPLAIN, and explain which one a parameterized/prepared query depends on and why a partition can still appear in the plan but never run. Then tell me the one thing that silently turns all of it off.
Pro concept
Full answer and evidence depth sit behind Pro
You have the question and a plain-English lead. Pro unlocks the short answer, what the docs say, what the code does, the labeled lab evidence or reproduction protocol, how to use it under pressure, and the references.
Unlock the full breakdown for Partition pruning (plan-time, init-time, exec-time)
- How you'd answer it, the full senior-level short answer
- What the docs say, the manual's actual wording, with the citations
- What the code does, the mechanism decoded from PostgreSQL's own source at a pinned tag
- Proof from a real run, labeled as raw output, a captured run summary, or a run-it-yourself protocol
- Using it under pressure, the situation, the call you'd make, what goes wrong, and what people get wrong
- Version notes, what changed across PostgreSQL releases
- 6 interviewer follow-ups for this concept
Card required. Cancel before day 7 and you are not charged.
How this was verified
The open teaser is the question and a plain-English lead. The short answer, the manual walkthrough, the source decode, the lab evidence, and how to use it under pressure unlock with Pro. Evidence is labeled as raw output, a captured run summary, or a run-it-yourself protocol.
Connected
Where this concept connects
How this concept links across the library, the interview questions that test it, its plain-English glossary definition, and the guided pathways it belongs to. Open the full map to explore further.
Part of these pathways
Related concepts