pg.ddx.io pgsql-admin@postgresql.org mailing list archive
help / color / mirror / Atom feedMemory and Swap
7+ messages / 5 participants
[nested] [flat]
* Memory and Swap
@ 2016-05-10 20:23 Campbell, Lance <lance@illinois.edu>
0 siblings, 3 replies; 7+ messages in thread
From: Campbell, Lance @ 2016-05-10 20:23 UTC (permalink / raw)
To: pgsql-admin
PostgreSQL 9.5.2
Linux Red Hat
I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
Yet my swap is at 1 G.
1) Why is that?
2) Over that past week it has climbed from almost nothing to 1 G. It is a steady climb. No big jump.
Thanks,
Lance
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-10 21:21 Scott Whitney <scott@journyx.com>
parent: Campbell, Lance <lance@illinois.edu>
2 siblings, 0 replies; 7+ messages in thread
From: Scott Whitney @ 2016-05-10 21:21 UTC (permalink / raw)
To: Campbell, Lance <lance@illinois.edu>; pgsql-admin
Swap happens under heavy load. At some point you hit a barrier that caused things to swap. Using swap in and of itself is not bad, and it is to be expected. Actual SWAPPING (happening all the time) means you're out of RAM, AND that's bad.
If you would like to talk to me directly about this, let me know. While I am not as good on the internals as The Big Brains on this list, I am certainly in the top on the IT end of it.
(Hi, Greg...you know what you did...)
Sent via the Samsung GALAXY S®4, an AT&T 4G LTE smartphone
-------- Original message --------
From: "Campbell, Lance" <lance@illinois.edu>
Date: 05/10/2016 3:25 PM (GMT-06:00)
To: "'pgsql-admin@postgresql.org'" <pgsql-admin@postgresql.org>
Subject: [ADMIN] Memory and Swap
PostgreSQL 9.5.2
Linux Red Hat
I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
Yet my swap is at 1 G.
1) Why is that?
2) Over that past week it has climbed from almost nothing to 1 G. It is a steady climb. No big jump.
Thanks,
Lance
Journyx, Inc.
7600 Burnet Road #300
Austin, TX 78757
www.journyx.com
p 512.834.8888
f 512-834-8858
Do you receive our promotional emails? You can subscribe or unsubscribe to those emails at http://go.journyx.com/emailPreference/e/4932/714/
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-11 05:37 Marco Nietz <pg@mnietz.de>
parent: Campbell, Lance <lance@illinois.edu>
2 siblings, 1 reply; 7+ messages in thread
From: Marco Nietz @ 2016-05-11 05:37 UTC (permalink / raw)
To: pgsql-admin
Linux tends to swap out to early with the default settings of
swappiness, try to decrease it to 10 or 1
https://en.wikipedia.org/wiki/Swappiness
Marco
Am 10.05.2016 um 22:23 schrieb Campbell, Lance:
> PostgreSQL 9.5.2
>
> Linux Red Hat
>
> I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
>
> Yet my swap is at 1 G.
>
> 1)Why is that?
>
> 2)Over that past week it has climbed from almost nothing to 1 G. It is
> a steady climb. No big jump.
>
> Thanks,
>
> Lance
>
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-11 18:51 Campbell, Lance <lance@illinois.edu>
parent: Marco Nietz <pg@mnietz.de>
0 siblings, 0 replies; 7+ messages in thread
From: Campbell, Lance @ 2016-05-11 18:51 UTC (permalink / raw)
To: 'Marco Nietz' <pg@mnietz.de>; pgsql-admin
Marco and Scott,
Thanks for your answers. The Swappiness web link was great.
Lance
-----Original Message-----
From: pgsql-admin-owner@postgresql.org [mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Marco Nietz
Sent: Wednesday, May 11, 2016 12:37 AM
To: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Memory and Swap
Linux tends to swap out to early with the default settings of swappiness, try to decrease it to 10 or 1
https://en.wikipedia.org/wiki/Swappiness
Marco
Am 10.05.2016 um 22:23 schrieb Campbell, Lance:
> PostgreSQL 9.5.2
>
> Linux Red Hat
>
> I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
>
> Yet my swap is at 1 G.
>
> 1)Why is that?
>
> 2)Over that past week it has climbed from almost nothing to 1 G. It
> is a steady climb. No big jump.
>
> Thanks,
>
> Lance
>
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-11 20:14 Fernando Hevia <fhevia@gmail.com>
parent: Campbell, Lance <lance@illinois.edu>
2 siblings, 1 reply; 7+ messages in thread
From: Fernando Hevia @ 2016-05-11 20:14 UTC (permalink / raw)
To: Campbell, Lance <lance@illinois.edu>; +Cc: pgsql-admin
I wouldn't worry about the system using swap while there is plenty of free
RAM available. As others have stated, it is a rather common situation. The
kernel might decide on moving some seldom accessed memory pages to swap in
order to make RAM available for future demand. But when RAM starts running
low, do keep and eye on how many bytes are actually being swapped. You can
use vmstat to show the amount of bytes being swapped in/out of the system.
I.e: vmstat output of a system with no swapping taking place and marginal
swap usage:
~# vmstat 5
procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy id
wa
2 0 28052 363992 156736 1251116 0 0 6 15 1 7 2 1 97
0
0 0 28052 363964 156736 1251128 0 0 0 13 759 283 2 2 96
0
0 0 28052 371132 156736 1251132 0 0 0 5 348 287 1 1 98
0
Any value > 0 means the system is actually reading from or writing to swap,
at the same time you should notice a severe downgrade of the system's
performance.
On Tue, May 10, 2016 at 5:23 PM, Campbell, Lance <lance@illinois.edu> wrote:
> PostgreSQL 9.5.2
>
> Linux Red Hat
>
>
>
> I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
>
>
>
> Yet my swap is at 1 G.
>
>
>
> 1) Why is that?
>
> 2) Over that past week it has climbed from almost nothing to 1 G.
> It is a steady climb. No big jump.
>
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-18 14:37 Campbell, Lance <lance@illinois.edu>
parent: Fernando Hevia <fhevia@gmail.com>
0 siblings, 1 reply; 7+ messages in thread
From: Campbell, Lance @ 2016-05-18 14:37 UTC (permalink / raw)
To: 'Fernando Hevia' <fhevia@gmail.com>; +Cc: pgsql-admin
Thanks for the reply.
What are the values that can appear in the column SI and SO? Are those disk blocks? Also how high would those numbers possibly get in those two columns before I should be concerned. I am noticing two digit number like 84. Every once in a while it will spike to something like 814.
Lance
From: Fernando Hevia [mailto:fhevia@gmail.com]
Sent: Wednesday, May 11, 2016 3:14 PM
To: Campbell, Lance <lance@illinois.edu>
Cc: pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Memory and Swap
I wouldn't worry about the system using swap while there is plenty of free RAM available. As others have stated, it is a rather common situation. The kernel might decide on moving some seldom accessed memory pages to swap in order to make RAM available for future demand. But when RAM starts running low, do keep and eye on how many bytes are actually being swapped. You can use vmstat to show the amount of bytes being swapped in/out of the system.
I.e: vmstat output of a system with no swapping taking place and marginal swap usage:
~# vmstat 5
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r b swpd free buff cache si so bi bo in cs us sy id wa
2 0 28052 363992 156736 1251116 0 0 6 15 1 7 2 1 97 0
0 0 28052 363964 156736 1251128 0 0 0 13 759 283 2 2 96 0
0 0 28052 371132 156736 1251132 0 0 0 5 348 287 1 1 98 0
Any value > 0 means the system is actually reading from or writing to swap, at the same time you should notice a severe downgrade of the system's performance.
On Tue, May 10, 2016 at 5:23 PM, Campbell, Lance <lance@illinois.edu<mailto:lance@illinois.edu>> wrote:
PostgreSQL 9.5.2
Linux Red Hat
I have 10 G of memory. Nagios is saying I have 2 G used and 8 G free.
Yet my swap is at 1 G.
1) Why is that?
2) Over that past week it has climbed from almost nothing to 1 G. It is a steady climb. No big jump.
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: Memory and Swap
@ 2016-05-18 15:09 Albe Laurenz <laurenz.albe@wien.gv.at>
parent: Campbell, Lance <lance@illinois.edu>
0 siblings, 0 replies; 7+ messages in thread
From: Albe Laurenz @ 2016-05-18 15:09 UTC (permalink / raw)
To: 'Campbell, Lance *EXTERN*' <lance@illinois.edu>; Fernando Hevia <fhevia@gmail.com>; +Cc: pgsql-admin
Lance Campbell wrote:
> What are the values that can appear in the column SI and SO? Are those disk blocks? Also how high
> would those numbers possibly get in those two columns before I should be concerned. I am noticing two
> digit number like 84. Every once in a while it will spike to something like 814.
The unit should be KB/s, check your vmstat man page.
Occasional "so" shouldn't be a problem, but if "si" is greater than 0 regularly,
you are probably memory constrained.
Yours,
Laurenz Albe
--
Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-admin
^ permalink raw reply [nested|flat] 7+ messages in thread
end of thread, other threads:[~2016-05-18 15:09 UTC | newest]
Thread overview: 7+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2016-05-10 20:23 Memory and Swap Campbell, Lance <lance@illinois.edu>
2016-05-10 21:21 ` Scott Whitney <scott@journyx.com>
2016-05-11 05:37 ` Marco Nietz <pg@mnietz.de>
2016-05-11 18:51 ` Campbell, Lance <lance@illinois.edu>
2016-05-11 20:14 ` Fernando Hevia <fhevia@gmail.com>
2016-05-18 14:37 ` Campbell, Lance <lance@illinois.edu>
2016-05-18 15:09 ` Albe Laurenz <laurenz.albe@wien.gv.at>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox