32 lines
990 B
PL/PgSQL
32 lines
990 B
PL/PgSQL
-- Internal function to generate stats for a table if they don't exist
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CREATE OR REPLACE FUNCTION _CDB_GenerateStats(reloid REGCLASS)
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RETURNS VOID
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AS $$
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DECLARE
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has_stats BOOLEAN;
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BEGIN
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SELECT EXISTS (
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SELECT * FROM pg_catalog.pg_statistic WHERE starelid = reloid
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) INTO has_stats;
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IF NOT has_stats THEN
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EXECUTE Format('ANALYZE %s;', reloid);
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END IF;
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END
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$$ LANGUAGE 'plpgsql' VOLATILE STRICT SECURITY DEFINER;
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-- Return a row count estimate of the result of a query using statistics
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CREATE OR REPLACE FUNCTION CDB_EstimateRowCount(query text)
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RETURNS Numeric
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AS $$
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DECLARE
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plan JSON;
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BEGIN
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-- Make sure statistics exist for all the tables of the query
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PERFORM _CDB_GenerateStats(tabname) FROM unnest(CDB_QueryTablesText(query)) AS tabname;
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-- Use the query planner to obtain an estimate of the number of result rows
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EXECUTE 'EXPLAIN (FORMAT JSON) ' || query INTO STRICT plan;
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RETURN plan->0->'Plan'->'Plan Rows';
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END
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$$ LANGUAGE 'plpgsql' VOLATILE STRICT;
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