pg_hint_plan makes it possible to tweak PostgreSQL execution plans using so-called "hints" in SQL comments, like /*+ SeqScan(a) */.

PostgreSQL uses a cost-based optimizer, that uses data statistics, not static rules. The planner (optimizer) estimates costs of each possible execution plans for a SQL statement, then executes the plan with the lowest cost. The planner does its best to select the best execution plan, but it is far from perfect, since it may not count some data properties, like correlation between columns.

For more details, please see the various documentations available in the docs/ directory:

1. Description
2. The hint table
3. Installation
4. Unistallation
5. Details in hinting
6. Errors
7. Functional limitations
8. Requirements
9. Hints list

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