/*
* See if the inner relation is provably unique for this outer rel.
*
- * We have some special cases: for JOIN_SEMI and JOIN_ANTI, it doesn't
- * matter since the executor can make the equivalent optimization anyway;
- * we need not expend planner cycles on proofs. For JOIN_UNIQUE_INNER, we
- * must be considering a semijoin whose inner side is not provably unique
- * (else reduce_unique_semijoins would've simplified it), so there's no
- * point in calling innerrel_is_unique. However, if the LHS covers all of
- * the semijoin's min_lefthand, then it's appropriate to set inner_unique
+ * We have some special cases: for JOIN_SEMI, it doesn't matter since the
+ * executor can make the equivalent optimization anyway. It also doesn't
+ * help enable use of Memoize, since a semijoin with a provably unique
+ * inner side should have been reduced to an inner join in that case.
+ * Therefore, we need not expend planner cycles on proofs. (For
+ * JOIN_ANTI, although it doesn't help the executor for the same reason,
+ * it can benefit Memoize paths.) For JOIN_UNIQUE_INNER, we must be
+ * considering a semijoin whose inner side is not provably unique (else
+ * reduce_unique_semijoins would've simplified it), so there's no point in
+ * calling innerrel_is_unique. However, if the LHS covers all of the
+ * semijoin's min_lefthand, then it's appropriate to set inner_unique
* because the path produced by create_unique_path will be unique relative
* to the LHS. (If we have an LHS that's only part of the min_lefthand,
* that is *not* true.) For JOIN_UNIQUE_OUTER, pass JOIN_INNER to avoid
switch (jointype)
{
case JOIN_SEMI:
- case JOIN_ANTI:
-
- /*
- * XXX it may be worth proving this to allow a Memoize to be
- * considered for Nested Loop Semi/Anti Joins.
- */
extra.inner_unique = false; /* well, unproven */
break;
case JOIN_UNIQUE_INNER:
return NULL;
/*
- * Currently we don't do this for SEMI and ANTI joins unless they're
- * marked as inner_unique. This is because nested loop SEMI/ANTI joins
- * don't scan the inner node to completion, which will mean memoize cannot
- * mark the cache entry as complete.
- *
- * XXX Currently we don't attempt to mark SEMI/ANTI joins as inner_unique
- * = true. Should we? See add_paths_to_joinrel()
+ * Currently we don't do this for SEMI and ANTI joins, because nested loop
+ * SEMI/ANTI joins don't scan the inner node to completion, which means
+ * memoize cannot mark the cache entry as complete. Nor can we mark the
+ * cache entry as complete after fetching the first inner tuple, because
+ * if that tuple and the current outer tuple don't satisfy the join
+ * clauses, a second inner tuple that satisfies the parameters would find
+ * the cache entry already marked as complete. The only exception is when
+ * the inner relation is provably unique, as in that case, there won't be
+ * a second matching tuple and we can safely mark the cache entry as
+ * complete after fetching the first inner tuple. Note that in such
+ * cases, the SEMI join should have been reduced to an inner join by
+ * reduce_unique_semijoins.
*/
- if (!extra->inner_unique && (jointype == JOIN_SEMI ||
- jointype == JOIN_ANTI))
+ if ((jointype == JOIN_SEMI || jointype == JOIN_ANTI) &&
+ !extra->inner_unique)
return NULL;
/*
ln := regexp_replace(ln, 'Heap Fetches: \d+', 'Heap Fetches: N');
ln := regexp_replace(ln, 'loops=\d+', 'loops=N');
ln := regexp_replace(ln, 'Index Searches: \d+', 'Index Searches: N');
+ ln := regexp_replace(ln, 'Memory: \d+kB', 'Memory: NkB');
return next ln;
end loop;
end;
RESET parallel_tuple_cost;
RESET parallel_setup_cost;
RESET min_parallel_table_scan_size;
+-- Ensure memoize works for ANTI joins
+CREATE TABLE tab_anti (a int, b boolean);
+INSERT INTO tab_anti SELECT i%3, false FROM generate_series(1,100)i;
+ANALYZE tab_anti;
+-- Ensure we get a Memoize plan for ANTI join
+SELECT explain_memoize('
+SELECT COUNT(*) FROM tab_anti t1 LEFT JOIN
+LATERAL (SELECT DISTINCT ON (a) a, b, t1.a AS x FROM tab_anti t2) t2
+ON t1.a+1 = t2.a
+WHERE t2.a IS NULL;', false);
+ explain_memoize
+--------------------------------------------------------------------------------------------
+ Aggregate (actual rows=1.00 loops=N)
+ -> Nested Loop Anti Join (actual rows=33.00 loops=N)
+ -> Seq Scan on tab_anti t1 (actual rows=100.00 loops=N)
+ -> Memoize (actual rows=0.67 loops=N)
+ Cache Key: (t1.a + 1), t1.a
+ Cache Mode: binary
+ Hits: 97 Misses: 3 Evictions: Zero Overflows: 0 Memory Usage: NkB
+ -> Subquery Scan on t2 (actual rows=0.67 loops=N)
+ Filter: ((t1.a + 1) = t2.a)
+ Rows Removed by Filter: 2
+ -> Unique (actual rows=2.67 loops=N)
+ -> Sort (actual rows=67.33 loops=N)
+ Sort Key: t2_1.a
+ Sort Method: quicksort Memory: NkB
+ -> Seq Scan on tab_anti t2_1 (actual rows=100.00 loops=N)
+(15 rows)
+
+-- And check we get the expected results.
+SELECT COUNT(*) FROM tab_anti t1 LEFT JOIN
+LATERAL (SELECT DISTINCT ON (a) a, b, t1.a AS x FROM tab_anti t2) t2
+ON t1.a+1 = t2.a
+WHERE t2.a IS NULL;
+ count
+-------
+ 33
+(1 row)
+
+-- Ensure we do not add memoize node for SEMI join
+EXPLAIN (COSTS OFF)
+SELECT * FROM tab_anti t1 WHERE t1.a IN
+ (SELECT a FROM tab_anti t2 WHERE t2.b IN
+ (SELECT t1.b FROM tab_anti t3 WHERE t2.a > 1 OFFSET 0));
+ QUERY PLAN
+-------------------------------------------------
+ Nested Loop Semi Join
+ -> Seq Scan on tab_anti t1
+ -> Nested Loop Semi Join
+ Join Filter: (t1.a = t2.a)
+ -> Seq Scan on tab_anti t2
+ -> Subquery Scan on "ANY_subquery"
+ Filter: (t2.b = "ANY_subquery".b)
+ -> Result
+ One-Time Filter: (t2.a > 1)
+ -> Seq Scan on tab_anti t3
+(10 rows)
+
+DROP TABLE tab_anti;
ln := regexp_replace(ln, 'Heap Fetches: \d+', 'Heap Fetches: N');
ln := regexp_replace(ln, 'loops=\d+', 'loops=N');
ln := regexp_replace(ln, 'Index Searches: \d+', 'Index Searches: N');
+ ln := regexp_replace(ln, 'Memory: \d+kB', 'Memory: NkB');
return next ln;
end loop;
end;
RESET parallel_tuple_cost;
RESET parallel_setup_cost;
RESET min_parallel_table_scan_size;
+
+-- Ensure memoize works for ANTI joins
+CREATE TABLE tab_anti (a int, b boolean);
+INSERT INTO tab_anti SELECT i%3, false FROM generate_series(1,100)i;
+ANALYZE tab_anti;
+
+-- Ensure we get a Memoize plan for ANTI join
+SELECT explain_memoize('
+SELECT COUNT(*) FROM tab_anti t1 LEFT JOIN
+LATERAL (SELECT DISTINCT ON (a) a, b, t1.a AS x FROM tab_anti t2) t2
+ON t1.a+1 = t2.a
+WHERE t2.a IS NULL;', false);
+
+-- And check we get the expected results.
+SELECT COUNT(*) FROM tab_anti t1 LEFT JOIN
+LATERAL (SELECT DISTINCT ON (a) a, b, t1.a AS x FROM tab_anti t2) t2
+ON t1.a+1 = t2.a
+WHERE t2.a IS NULL;
+
+-- Ensure we do not add memoize node for SEMI join
+EXPLAIN (COSTS OFF)
+SELECT * FROM tab_anti t1 WHERE t1.a IN
+ (SELECT a FROM tab_anti t2 WHERE t2.b IN
+ (SELECT t1.b FROM tab_anti t3 WHERE t2.a > 1 OFFSET 0));
+
+DROP TABLE tab_anti;
projects / thirdparty / postgresql.git / commitdiff
