Hello all,
We are trying to debug some slow performance in our production environment
(Amazon RDS, Postgresql 9.6.11), and we’re looking at a particular EXPLAIN node
that seems… weird. This is a very large query involving a number of joins, but
it performs pretty well in our staging environment (which has roughly the same
data set as production, with a few tweaks). However, there is one node in the
EXPLAIN plan that is wildly different:
In the staging environment, we get this:
Index Scan using "programPK" on public.program prog (cost=0.29..0.35 rows=1
width=16) (actual time=0.002..0.003 rows=1 loops=21965)
Output: prog.id, prog.version, prog.active, prog.created_date,
prog.last_modified_date, prog.created_by, prog.last_modified_by,
prog.client_id, prog.scheme_id, prog.name, prog.legacy_group_id,
prog.custom_fields, prog.setup_complete, prog.setup_messages,
prog.legacy_program_type
Index Cond: (prog.id = per.program)
Buffers: shared hit=87860
In the production environment, we get this:
Index Scan using "programPK" on public.program prog (cost=0.29..0.36 rows=1
width=16) (actual time=0.017..4.251 rows=1 loops=21956)
Output: prog.id, prog.version, prog.active, prog.created_date,
prog.last_modified_date, prog.created_by, prog.last_modified_by,
prog.client_id, prog.scheme_id, prog.name, prog.legacy_group_id,
prog.custom_fields, prog.setup_complete, prog.setup_messages,
prog.legacy_program_type
Index Cond: (prog.id = per.program)
Buffers: shared hit=25437716
The tables in both environments are about the same size (18MB) and the indexes
are about the same size (360kb/410kb) – and the shared hits are pretty much the
same on the other nodes of the query between the two environments.
Lastly, if we take out the join to the “program” table, the query performs much
faster in production and the timing between staging and production is similar.
This has happened one time before, and we did a “REINDEX” on the program table
– and that made the problem mostly go away. Now it seems to be back, and I’m
not sure what to make of it.
Thanks in advance for any help you can offer!
Scott
SCOTT RANKIN
VP, Technology
Motus, LLC
Two Financial Center, 60 South Street, Boston, MA 02111
617.467.1900 (O) | [email protected]<mailto:[email protected]>
Follow us on LinkedIn<https://www.linkedin.com/company/motus-llc/> | Visit us
at motus.com<http://www.motus.com/>
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.
