-- =========== Test #1 =========== --

BEGIN;
SET enable_seqscan TO false; SET enable_bitmapscan TO false; SET enable_hashjoin TO false; SET enable_mergejoin TO false;
EXPLAIN ANALYZE SELECT * FROM threads AS thr JOIN msgs AS msg ON msg.thrid = thr.id WHERE thr.forid = 1 ORDER BY thr.id DESC, msg.msgid DESC LIMIT 100;
ROLLBACK;

                                                                            QUERY PLAN                                                                   
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=64537577.92..64537677.92 rows=100 width=447) (actual time=61923.813..61924.379 rows=100 loops=1)
   ->  Sort  (cost=64537577.92..64633839.92 rows=96262 width=447) (actual time=61923.804..61924.038 rows=100 loops=1)
         Sort Key: thr.id, msg.msgid
         ->  Nested Loop  (cost=0.00..61339121.37 rows=96262 width=447) (actual time=0.248..40366.113 rows=431350 loops=1)
               ->  Index Scan using threads_uni_forid_id on threads thr  (cost=0.00..14229.22 rows=2850 width=176) (actual time=0.127..5246.470 rows=8339 loops=1)
                     Index Cond: (forid = 1)
               ->  Index Scan using msgs_pkey on msgs msg  (cost=0.00..12595.51 rows=2974 width=271) (actual time=1.544..4.000 rows=52 loops=8339)
                     Index Cond: (msg.thrid = "outer".id)
 Total runtime: 62079.452 ms
(9 rows)






-- =========== Test #2 =========== --

EXPLAIN ANALYZE SELECT * FROM threads AS thr JOIN msgs AS msg ON msg.thrid = thr.id WHERE thr.forid = 1 ORDER BY thr.id DESC LIMIT 100;

                                                                             QUERY PLAN                                                                    
----------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.00..63721.01 rows=100 width=447) (actual time=9.579..10.775 rows=100 loops=1)
   ->  Nested Loop  (cost=0.00..61339121.37 rows=96262 width=447) (actual time=9.574..10.438 rows=100 loops=1)
         ->  Index Scan Backward using threads_uni_forid_id on threads thr  (cost=0.00..14229.22 rows=2850 width=176) (actual time=0.082..0.145 rows=4 loops=1)
               Index Cond: (forid = 1)
         ->  Index Scan using msgs_pkey on msgs msg  (cost=0.00..12595.51 rows=2974 width=271) (actual time=2.399..2.475 rows=25 loops=4)
               Index Cond: (msg.thrid = "outer".id)
 Total runtime: 11.071 ms
(7 rows)