On 3/31/2015 10:31 AM, Mike Roest wrote:
Hi there,
I'm having an issue with query performance between 2 different pgsql
environments.
Ther first is our current production postgres server with is running
9.3.5 on Centos 5 x64. The second system is Amazon's RDS postgres as a
service. On our local DB server we have a query that executes in a
reasonable amount of time (600 msec). On RDS the query will run for
more then 10 minutes on a similarly CPU specced systems. I've been
working through with Amazon support and I'm looking for more suggestions
on where to look (both for me and to direct Amazon). The RDS system
does use a network filesystem while our production server is a local
RAID10 array, I can see that effecting the actual performance of the
query but not the query planner costing (unless there's an input to
query planner costing that I can't find)
The Query plan costs generated by the 2 systems are vastly different,
while the plans themselves are basically identical other then the
materialization that RDS is doing (if I disable the materialization then
they are almost the same other then a seq scan/heap scan on one small
<2000 row table). All the tables in the query have been analyzed on
each server without any impact
Current Production
Explain:
http://explain.depesz.com/s/Tkyc
Explain Analyze
http://explain.depesz.com/s/UnQt
RDS: (with enable_material=off)
http://explain.depesz.com/s/vDiV
(with enable_material=on)
http://explain.depesz.com/s/HUjx
I have validated that all the query planning configuration variables on
this page
http://www.postgresql.org/docs/9.3/static/runtime-config-query.html are
the same between the 2 environments. If I modify the local production
system values for things like random_page_cost and seq_page_cost to
absurd values like 60000 I can get it to generate a similar planner
cost. Similarly if I lower the RDS values to absurdly low values like
.00000001 I can get it to generate a similarly costed plan (while still
performing horridly).
I've reached the end of things I can think about (I'm also working on
rewriting the query but it's a generated query out of a infrastructure
component so it's not a simple change).
Just looking for any ideas on additional things to look into.
The query is available here:
https://www.dropbox.com/s/m31ct6k0mod0576/simplifiedquery.sql?dl=0
--
Data's inconvienient when people have opinions.
Seems like there is no useable index on table timesheet. It always
seems to table scan all 99K rows, several times.
I'll bet on RDS that table scan is super slow.
The RDS plans seem to be just explain? I assume its too slow to run an
explain analyze on? Would be neat to see explain analyze from RDS.
(any way to add a little extra where magic to cut the rows down to a
useable, but still slow, sample?)
On this one:
http://explain.depesz.com/s/UnQt
Line 11 table scans 99K rows, then all those rows are carried up the
chain (lines 10, 9, 8, 7 and 6). Any way to reduce the row count
earlier? Line 5 finally seems to filter out 94K rows.
Would be neat to see if these are buffered reads or are actually hitting
disk too. (something like EXPLAIN (ANALYZE, BUFFERS) select...)
-Andy
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