Week 09 (23)

More notes on explain output:

each major entry corresponds to a plan node
- e.g. Seq Scan, Index Scan, Hash Join, Merge Join, ...
some nodes include additional qualifying information
- e.g. Filter, Index Cond, Hash Cond, Buckets, ...
cost values in explain are estimates (notional units)
explain analyze also includes actual time costs (ms)
costs of parent nodes include costs of all children
estimates of #results based on sample of data