Hi,
2017-11-07 16:11 GMT+01:00 Andres Freund <andres@xxxxxxxxxxx>:
Hi,
On 2017-11-07 11:11:36 +0100, Ulf Lohbrügge wrote:
> I'm using PostgreSQL 9.5.9 on Debian and experience slow execution of some
> basic SET statements.
>
> I created about 1600 roles and use that setup for a multi tenancy
> application:
Hm. How often do you drop/create these roles? How many other
roles/groups is one role a member of?
I create between 10-40 roles per day.
The roles tenant1 to tenant1600 are not members of any other roles. Only the role 'admin' is member of many roles (tenant1 to tenant1600).
> My application solely uses the role 'admin' to connect to the database.
> When performing sql statements for a specific tenant (e.g. tenant1337), a
> connection with user 'admin' is established and the following commands are
> executed:
>
> SET ROLE 1337;
> SET search_path = tenant1337;
>
> Then the application uses that connection to perform various statements in
> the database.
Just to be sure: You realize bad application code could escape from
that, right?
Yes, I do. :)
My application executes all statements via an ORM tool (Hibernate). But evil code could still get the plain DB-Connection and execute "SET ROLE ..." statements. My application used to connect as tenant1 to tenant1600 but that lead to a vast amount of postgresql connections (even with pgbouncer).
> My application is a web service that approximately executes some hundred
> statements per second.
>
> I set "log_min_duration_statement = 200ms" and I get about 2k to 4k lines
> per day with statements like "SET ROLE"", "SET search_path ..." and "RESET
> ROLE":
>
> --snip--
> 2017-11-07 09:44:30 CET [27760]: [3-1] user=admin,db=mydb LOG: duration:
> 901.591 ms execute <unnamed>: SET ROLE "tenant762"
> 2017-11-07 09:44:30 CET [27659]: [4-1] user=admin,db=mydb LOG: duration:
> 1803.971 ms execute <unnamed>: SET ROLE "tenant392"
That is weird.
> Besides those peaks in statement duration, my application performs (i.e.
> has acceptable response times) most of the time.
>
> Is there anything I can do to improve performance here?
> Any help is greatly appreciated!
Can you manually reproduce the problem? What times do you get if you
manually run the statement?
Unfortunately not. Every time I manually execute "SET ROLE ..." the statement is pretty fast. I created a simple SQL file that contains the following statements:
--snip--
SET ROLE tenant382;
SET ROLE tenant1337;
SET ROLE tenant2;
-- repeat the lines above 100k times
--snap--
When I execute those statements via 'time psql < set-roles.sql', the call lasts 138,7 seconds. So 300k "SET ROLE" statements result in 0,46ms per call on average.
Cheers,
Ulf
