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Support parameterized TidPaths.

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Up to now we've not worried much about joins where the join key is a
relation's CTID column, reasoning that storing a table's CTIDs in some
other table would be pretty useless.  However, there are use-cases for
this sort of query involving self-joins, so that argument doesn't really
hold water.

This patch allows generating plans for joins on CTID that use a nestloop
with inner TidScan, similar to what we might do with an index on the join
column.  This is the most efficient way to join when the outer side of
the nestloop is expected to yield relatively few rows.

This change requires upgrading tidpath.c and the generated TidPaths
to work with RestrictInfos instead of bare qual clauses, but that's
long-postponed technical debt anyway.

Discussion: https://postgr.es/m/17443.1545435266@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2018-12-30 15:24:28 -05:00
parent 6f19a8c41f
commit b5415e3c21
8 changed files with 418 additions and 143 deletions
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55
src/test/regress/expected/tidscan.out
View File

@ -40,6 +40,22 @@ SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
(0,1) | 1
(1 row)
-- OR'd clauses
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
QUERY PLAN
--------------------------------------------------------------
Tid Scan on tidscan
TID Cond: ((ctid = '(0,2)'::tid) OR ('(0,1)'::tid = ctid))
(2 rows)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(2 rows)
-- ctid = ScalarArrayOp - implemented as tidscan
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
@ -92,6 +108,45 @@ WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
(0,3) | 3
(2 rows)
-- nestloop-with-inner-tidscan joins on tid
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
QUERY PLAN
------------------------------------
Nested Loop
-> Seq Scan on tidscan t1
Filter: (id = 1)
-> Tid Scan on tidscan t2
TID Cond: (ctid = t1.ctid)
(5 rows)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
ctid | id | ctid | id
-------+----+-------+----
(0,1) | 1 | (0,1) | 1
(1 row)
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
QUERY PLAN
------------------------------------
Nested Loop Left Join
-> Seq Scan on tidscan t1
Filter: (id = 1)
-> Tid Scan on tidscan t2
TID Cond: (t1.ctid = ctid)
(5 rows)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
ctid | id | ctid | id
-------+----+-------+----
(0,1) | 1 | (0,1) | 1
(1 row)
-- exercise backward scan and rewind
BEGIN;
DECLARE c CURSOR FOR

17
src/test/regress/sql/tidscan.sql
View File

@ -17,6 +17,11 @@ EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
-- OR'd clauses
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
-- ctid = ScalarArrayOp - implemented as tidscan
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
@ -34,6 +39,18 @@ WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
SELECT ctid, * FROM tidscan
WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
-- nestloop-with-inner-tidscan joins on tid
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
-- exercise backward scan and rewind
BEGIN;
DECLARE c CURSOR FOR