On 11/30/18 7:53 AM, John Smith wrote:
We have a long script of sql that we run, several thousand lines of sql.
If I execute the script from start to finish, somewhere in the middle of
it, one sql command will hang and take 2 to 3 hours. During this time,
"htop" shows 100% cpu usage with a postgresql process, so it appears to
be doing something.
First, a naming note. psql is the name of the Postgres command line
client. What you are actually referring to is the Postgres server.
Second, without the actual commands solving this is going to be
difficult to impossible.
That being said I would suspect some sort of locking issue. I would
start with pg_stat_activity:
https://www.postgresql.org/docs/10/monitoring-stats.html#PG-STAT-ACTIVITY-VIEW
See what it says when you are in the 'hung' phase.
If I stop that command, then immediately rerun the rest of the script
starting from the command that "hung", the "hung" command then completes
in 5 seconds and the rest of the script just continues on perfectly. I
can interrupt the command within 30 mins of hanging, or 2 hours of
hanging; regardless of when I interrrupt the hung command, it always
immediately completes successully in < 5 seconds when I rerun the script
immediately after that.
I have noticed this in multiple scripts, multiple commands; one was an
"insert into", a different script hung on a "update" and a third one
would hang on a "create table x as (select ... )". These are all short
running commands normally, and we have indexes on all the columns for
the appropriate "where" clauses.
I can't send the sql (forbidden), but the actual command does not appear
to be the issue. Rerunning the same little section of sql manually which
includes the hung command, always takes less than a minute, but the
entire sql which should only take 30 minutes in total will always hang
at the same spot; and then interrupting it (regardless of how long it
was running) and rerunning immediately completes.
The "hung" command does eventually finish at times after 2 to 3 hours,
most often we can't afford to wait for it to run since this batch of sql
has to run daily.
Some other notes:
- Environment is Ubuntu 16.04; postgresql version was originaly 9.5(?)
but we have upgraded to 11.1 using postgresql packages for ubuntu and
the problem has persisted across postgresql versions.
- There are no other queries running on the postgresql server during
this time, and server load is idling (other than whatever psql is doing).
- It is an amazon server, with ZFS as the files system, it has 50% disk
free on this storage partition that postgresql database is on.
- We have 60 gigs of ram total, 8 cores.
- We have run the entire script using "create unlogged table" everywhere
as well, no difference.
- We have made tunings to the postgresql configuration to make it use
more RAM.
- All sql commands are sent through a custom Java application; so we use
java + JDBC to connect to postgresql for this. The script has custom
commands which are interpreted by the Java app, so we can't test running
the exact script start to finish in psql native tools since the native
tools won't understand our custom sql. However the java app is very
simple. All individual sql commands are committed immediately after they
run so there is no long transaction in play here. The psql jdbc driver
is "postgresql-42.2.4".
- One may suspect the custom java app; but again, htop shows postgresql
using 100% CPU usage on one core, so postgresql is chewing on the
command, doing something.
I have attached our current postgresql.conf file.
We're kind of pulling out our hair here, any ideas?
Thanks!
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
