sync-indexes: create expression statistics alongside identifier indexes - #95
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An identifier expression index lets Postgres find rows by a JSONB key, but the planner has no cardinality statistics for the expression, so it defaults to a poor n_distinct and mis-estimates selectivity. For a batch identifier lookup (WHERE identifier->>'k' = ANY / JOIN VALUES) it then prefers a full-partition hash join over a per-key index nested loop, so a large table stays slow despite the index (observed: a keyword lookup estimated 151 rows/lookup vs 1 actual, and picked a full scan of a 181k-row partition, ~2s/chunk). create_identifier_indexes now also creates table-level expression statistics (CREATE STATISTICS ... ON (<expr>), PostgreSQL 14+) on the same expression(s), and runs ANALYZE once so they take effect immediately. With real n_distinct the planner chooses the index nested loop on its own -- no planner hints, and safe when no index exists (the hash join stays the correct default). Adds a Postgres-14+ test asserting the statistics are created. Claude-Session: https://claude.ai/code/session_01B5EfLJqoafjW1FhvkxGSmg
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An identifier expression index lets Postgres find rows by a JSONB key, but the planner has no cardinality statistics for the expression, so it defaults to a poor n_distinct and mis-estimates selectivity. For a batch identifier lookup (WHERE identifier->>'k' = ANY / JOIN VALUES) it then prefers a full-partition hash join over a per-key index nested loop, so a large table stays slow despite the index (observed: a keyword lookup estimated 151 rows/lookup vs 1 actual, and picked a full scan of a 181k-row partition, ~2s/chunk).
create_identifier_indexes now also creates table-level expression statistics (CREATE STATISTICS ... ON (), PostgreSQL 14+) on the same expression(s), and runs ANALYZE once so they take effect immediately. With real n_distinct the planner chooses the index nested loop on its own -- no planner hints, and safe when no index exists (the hash join stays the correct default). Adds a Postgres-14+ test asserting the statistics are created.