From: Jim Nasby <Jim.Nasby@BlueTreble.com>
To: Jason Jho <jasonjho@gmail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Hanging query on a fresh restart
Date: Fri, 13 Nov 2015 15:40:42 -0600
Message-ID: <564658DA.2000804@BlueTreble.com> (raw)
In-Reply-To: <CACLReKuBuHU85p38fYoF_h_jMKeeFewOXvS7zSGV+fHWz4ENrQ@mail.gmail.com>
References: <CACLReKuBuHU85p38fYoF_h_jMKeeFewOXvS7zSGV+fHWz4ENrQ@mail.gmail.com>
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On 11/10/15 3:42 PM, Jason Jho wrote:
> On one particular day, this query hung for many hours and even while we
> killed pids for running queries and any locks granted, the query would
> never return. Also no hints of blocking processes. After some digging
> through some I/O metrics, we didn't see any memory issues or unusual
> spikes that would lead us to believe that we're running low on resources.
Did IO stats indicate IO was happening? Did you see a pegged CPU running
the query?
> There is 1 caveat, however: there was a different schema that contained
> a day-old copy of data that isn't normally present when the hang started
> to occur. However, since these are completely different schema
> namespaces with no crossovers in the queries themselves, I don't see how
> this is relevant.
If search_path wasn't what you thought it was you could have easily been
running against the wrong set of tables.
> We thought this might be possibly due to some internal vacuuming, but
> this is unlikely since there are no real concurrent reads or updates
> happening. Auto-vacuum is also on with default settings.
There are other reasons why autovacuum could kick in, notably to prevent
transaction ID wraparound.
> What is the most confusing part in all of this is why a DROP SCHEMA
> CASCADE and a fresh pg_restore would somehow fix the problem. Even a
> fresh reboot didn't fix it.
Without more info we're stuck guessing. You might try submitting a
ticket with amazon, especially if you can reproduce this.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
--
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To: pgsql-performance@postgresql.org
Cc: Jim.Nasby@BlueTreble.com, jasonjho@gmail.com
Subject: Re: Hanging query on a fresh restart
In-Reply-To: <564658DA.2000804@BlueTreble.com>
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