Picking random row from query with an exists where clause seem slow - postgresql

Question

I am trying to pick a random row from a table with what seems like a simple condition which includes it should be present in another table as well having a specific type.
select * from table1 t1 where type='Other' and exists (select 1 from table2 t2 where t2.id = t1.id FETCH FIRST ROW ONLY) order by random() limit 1;
I am trying to cut the selection in the second table short by only picking the first row it finds, I am really just interested if any row in that table exists, so one will do. However the time it took to run didn't change anything really. I've also tried joining the tables instead, that took twice as long it seems. Right now it takes a little over a minute to run, I am trying to cut this down to a few seconds, max 10.
Any ideas? The type could change in the query, it needs to be a generic index, not a specific one for "Other", there are hundreds of types.
Table1 has over +10M rows with unique id's, table2 has +95M.
I have an index on the id's as well as type
CREATE INDEX type_idx ON table1 USING btree (type);
CREATE INDEX id_idx ON table2 USING btree (id);
CREATE UNIQUE INDEX table1_pkey ON table1 USING btree (id);
Here is the explain
Limit (cost=297536.80..297536.80 rows=1 width=51) (actual time=68436.446..68456.389
rows=1 loops=1)
Buffers: shared hit=1503764 read=299217
I/O Timings: read=199577.751
-> Sort (cost=297536.80..297586.31 rows=19807 width=51) (actual
time=68436.444..68456.386 rows=1 loops=1)
Sort Key: (random())
Sort Method: top-N heapsort Memory: 25kB
Buffers: shared hit=1503764 read=299217
I/O Timings: read=199577.751
-> Gather (cost=7051.90..297437.76 rows=19807 width=51) (actual
time=117.271..68418.453 rows=58327 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=1503764 read=299217
I/O Timings: read=199577.751
-> Nested Loop Semi Join (cost=6051.90..294407.54 rows=8253 width=43)
(actual time=84.291..68358.619 rows=19442 loops=3)
Buffers: shared hit=1503764 read=299217
I/O Timings: read=199577.751
-> Parallel Bitmap Heap Scan on table1 t1 (cost=6051.46..135601.49
rows=225539 width=43) (actual time=83.250..24802.725 rows=185267 loops=3)
Recheck Cond: ((type)::text = 'Other'::text)
Rows Removed by Index Recheck: 1119917
Heap Blocks: exact=20174 lossy=11038
Buffers: shared read=94319
I/O Timings: read=72301.594
-> Bitmap Index Scan on type_idx (cost=0.00..5916.13
rows=541293 width=0) (actual time=89.207..89.208 rows=555802 loops=1)
Index Cond: ((type)::text = 'Other'::text)
Buffers: shared read=470
I/O Timings: read=33.209
-> Index Only Scan using id_idx on events (cost=0.44..65.15
rows=257 width=8) (actual time=0.234..0.234 rows=0 loops=555802)
Index Cond: (t2.id = t1.id)
Heap Fetches: 461
Buffers: shared hit=1503764 read=204898
I/O Timings: read=127276.157
Planning:
Buffers: shared hit=8 read=8
I/O Timings: read=3.139
Planning Time: 5.713 ms
Execution Time: 68457.688 ms
Here is the explain plan after I changed the type index to also include the id
Limit (cost=305876.92..305876.92 rows=1 width=51) (actual
time=81055.897..81077.393 rows=1 loops=1)
Buffers: shared hit=1501397 read=303247
I/O Timings: read=237093.600
-> Sort (cost=305876.92..305926.44 rows=19807 width=51) (actual
time=81055.895..81077.390 rows=1 loops=1)
Sort Key: (random())
Sort Method: top-N heapsort Memory: 25kB
Buffers: shared hit=1501397 read=303247
I/O Timings: read=237093.600
-> Gather (cost=15392.02..305777.89 rows=19807 width=51)
(actual time=87.662..81032.107 rows=58327 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=1501397 read=303247
I/O Timings: read=237093.600
-> Nested Loop Semi Join (cost=14392.02..302747.67
rows=8253 width=43) (actual time=73.967..80990.425 rows=19442
loops=3)
Buffers: shared hit=1501397 read=303247
I/O Timings: read=237093.600
-> Parallel Bitmap Heap Scan on table1 t1
(cost=14391.58..143941.61 rows=225539 width=43) (actual
time=73.193..20476.307 rows=185267 loops=3)
Recheck Cond: ((type)::text =
'Other'::text)
Rows Removed by Index Recheck: 1124091
Heap Blocks: exact=20346 lossy=11134
Buffers: shared read=95982
I/O Timings: read=59211.444
-> Bitmap Index Scan on type_idx
(cost=0.00..14256.26 rows=541293 width=0) (actual
time=73.552..73.552 rows=555802 loops=1)
Index Cond: ((type)::text =
'Other'::text)
Buffers: shared read=2133
I/O Timings: read=6.812
-> Index Only Scan using id_idx on table2
(cost=0.44..65.15 rows=257 width=8) (actual time=0.326..0.326
rows=0 loops=555802)
Index Cond: (t2.id = t1.id)
Heap Fetches: 461
Buffers: shared hit=1501397 read=207265
I/O Timings: read=177882.156
Planning:
Buffers: shared hit=29 read=10
I/O Timings: read=4.789
Planning Time: 11.993 ms
Execution Time: 81078.404 ms

Answer 1

Could you try a combination of columns in your index:
CREATE INDEX type_id_idx ON table1 USING btree (type, id);
How does this change the query plan?