On 11/28/18, 2:18 PM, "Justin Pryzby" <pry...@telsasoft.com> wrote:
On Wed, Nov 28, 2018 at 07:08:53PM +0000, Scott Rankin wrote:
> We recently moved our production database systems from a 9.4 running on a
self-managed EC2 instance to 9.6.10 on Amazon’s AWS (same RAM, CPU). After the
move, we’re finding that certain queries that we run against a GIN full-text
index have some occasionally very slow executions and I’m struggling to figure
out what to do about it. I would be very grateful for any ideas!
>
> The setup we have is a 32-core, 244 GB RAM primary with a same-sized read
replica. The queries are running off the replica, but performance is roughly
the same between the master and the replica.
>
> Here’s a query that’s performing badly:
Can you compare or show the explain(analyze,buffers) for a fast query
instance
vs slow query instance ? Is it slower due to index access or heap? Due to
cache misses ?
If I reduce the number of search terms in , I get this:
SELECT ls.location AS locationId FROM location_search ls WHERE ls.client =
83 AND search_field_tsvector @@ to_tsquery('9000:*'::text) AND ls.favorite =
TRUE LIMIT 100
Limit (cost=13203.99..13627.40 rows=100 width=8) (actual time=66.568..66.759
rows=100 loops=1)
Buffers: shared hit=1975
-> Bitmap Heap Scan on location_search ls (cost=13203.99..13923.79 rows=170
width=8) (actual time=66.568..66.729 rows=100 loops=1)
Recheck Cond: ((search_field_tsvector @@ to_tsquery('9000:*'::text))
AND (client = 83))
Filter: favorite
Heap Blocks: exact=86
Buffers: shared hit=1975
-> BitmapAnd (cost=13203.99..13203.99 rows=170 width=0) (actual
time=66.471..66.472 rows=0 loops=1)
Buffers: shared hit=1889
-> Bitmap Index Scan on location_search_tsvector_idx
(cost=0.00..2235.02 rows=11570 width=0) (actual time=20.603..20.604 rows=29155
loops=1)
Index Cond: (search_field_tsvector @@
to_tsquery('9000:*'::text))
Buffers: shared hit=546
-> Bitmap Index Scan on location_search_client_idx
(cost=0.00..10968.63 rows=442676 width=0) (actual time=40.682..40.682
rows=482415 loops=1)
Index Cond: (client = 83)
Buffers: shared hit=1343
Planning time: 0.181 ms
Execution time: 66.806 ms
I see almost no IO reads, and pg_stat_statements shows no cache misses.
Also, you have big ram - have you tried disabling KSM or THP ?
https://www.postgresql.org/message-id/20170718180152.GE17566%40telsasoft.com
Since this is Amazon RDS, we don't have any control over or access to the
underlying OS. I know that huge_page support is on for these instances. I
would hope that Amazon's already done that...
Justin
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