Thanks for the rely.
I have trialed the ionice -c 2 -n 7 tar…. change to our backup script and it 
appears to have helped but not by much.
The affected queries are more of the update/delete/insert queries. Could 
pg_start_backup be causing locking of some sort.

From: Rene Romero Benavides [mailto:rene.romer...@gmail.com]
Sent: Wednesday, 21 February 2018 1:37 AM
To: Laurenz Albe <laurenz.a...@cybertec.at>
Cc: Dylan Luong <dylan.lu...@unisa.edu.au>; pgsql-general@lists.postgresql.org
Subject: Re: Performance issues during backup

What about sending the backup to a different server? through ssh / rsync or 
something, that would save lots of IO activity

2018-02-20 2:02 GMT-06:00 Laurenz Albe 
Dylan Luong wrote:
> We perform nighty base backup of our production PostgreSQL instance. We have 
> a script that basically puts the instance
> into back mode and then backs up (tar) the /Data directory and then takes it 
> out of backup mode.
> Ie,
> psql -c "SELECT pg_start_backup('${DATE}');"
> tar -cvf - ${DATA_DIR} --exclude ${DATA_DIR}/pg_log | split -d -b 
> psql -c "SELECT pg_stop_backup();"
> The size of our database is about 250GB and it usually takes about 1 hour to 
> backup.
> During this time, we have performance issue where queries can take up to 
> 15secs to return where normally it takes 2 to 3 seconds.
> During this time (1:30am) usage is low (less than 10 users) on the system.
> Has anyone experience the same problem and any suggestions where to look at 
> to resolve the problem?

The "tar" is probably taking up too much I/O bandwidth.

Assuming this is Linux, you could run it with

  ionice -c 2 -n 7 tar ...


  ionice -c 3 tar ...

Of course then you can expect the backup to take more time.

Laurenz Albe
Cybertec | https://www.cybertec-postgresql.com

El genio es 1% inspiración y 99% transpiración.
Thomas Alva Edison

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