planner-cost-model
Skill1 starsChanged 6 months agoPostgreSQLView on GitHub
PostgreSQL's cost model — how the planner estimates query cost to pick among candidate plans. Covers `src/backend/optimizer/path/costsize.c` (the cost functions: `cost_seqscan`, `cost_index`, `cost_bitmap_heap_scan`, `cost_nestloop`, `cost_mergejoin`, `cost_hashjoin`, `cost_sort`, `cost_hashagg`, `cost_windowagg`, etc.) plus the cost GUCs (`seq_page_cost`, `random_page_cost`, `cpu_tuple_cost`, `cpu_index_tuple_cost`, `cpu_operator_cost`, `parallel_setup_cost`, `parallel_tuple_cost`, `jit_*_cost`). Loads when the user asks about cost estimation, why a plan differs from expected, how to tune cost GUCs, what units the numbers are in, or when to touch a specific `cost_*` function. Skip when the ask is about selectivity estimation (that's `clauselist_selectivity` and extended-stats territory) or about the actual EXPLAIN output rendering.
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The file
We split this skill into the rules it gives an agent
7 rules. About 0 are common, 5 are distinctive, and 2 are very specific to this project.
≈0
Common · estimate
Many files like this have a rule of this kind.
≈5
Distinctive · estimate
This author's own choices. Worth a look.
2
Very specific
Tied to their project's names, files or tools. Probably skip.
Licensed with conditions — read it at the source. We count its rules but don't quote them. Read them on GitHub.
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
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