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Re: commit so slow program looks frozen

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Carlo Stonebanks <stonec(dot)register(at)sympatico(dot)ca>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: commit so slow program looks frozen
Date: 2006-10-25 18:19:10
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Carlo Stonebanks wrote:

> The delays are so long that I used to think the app was hopelessly frozen. 
> By accident, I left the app alone in its frozen state and came back a good 
> deal later and seen that it was running again.
> Sometimes I decide it *IS* frozen and have to restart. Because Ctrl-C will 
> not cause the script to break, it appears the app is stuck in non-TCL code 
> (either waiting for postgres or stuck in the interface code?)

You may try to figure out what's the process doing (the backend
obviously, not the frontend (Tcl) process) by attaching to it with
strace.  Is it doing system calls?  Maybe it's busy reading from or
writing to disk.  Maybe it's swamped by a context switch storm (but in
that case, probably the other processes would be affected as well).

Or you may want to attach to it with GDB and see what the backtrace
looks like.  If nothing obvious pops up, do it several times and compare

I wouldn't expect it to be stuck on locks, because if it's only on
commit, then it probably has all the locks it needs.  But try to see if
you can find something not granted in pg_locks that it may be stuck on.

Alvaro Herrera                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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