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