On 11/28/18, 2:18 PM, "Justin Pryzby" <[email protected]> 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
This email message contains information that Motus, LLC considers confidential
and/or proprietary, or may later designate as confidential and proprietary. It
is intended only for use of the individual or entity named above and should not
be forwarded to any other persons or entities without the express consent of
Motus, LLC, nor should it be used for any purpose other than in the course of
any potential or actual business relationship with Motus, LLC. If the reader of
this message is not the intended recipient, or the employee or agent
responsible to deliver it to the intended recipient, you are hereby notified
that any dissemination, distribution, or copying of this communication is
strictly prohibited. If you have received this communication in error, please
notify sender immediately and destroy the original message.
Internal Revenue Service regulations require that certain types of written
advice include a disclaimer. To the extent the preceding message contains
advice relating to a Federal tax issue, unless expressly stated otherwise the
advice is not intended or written to be used, and it cannot be used by the
recipient or any other taxpayer, for the purpose of avoiding Federal tax
penalties, and was not written to support the promotion or marketing of any
transaction or matter discussed herein.
