Re: How do you detect memory issues ?
Date: Thu, 6 Dec 2018 01:26:50 -0500
Message-ID: <ed06b3f0-8f76-1b46-e8d6-2e2a76e095d8_at_gmail.com>
Hi Kyle,
You are talking about vmstat. I prefer sar. Here is the output of sar -B
3 3:
mgogala_at_umajor:~$ sar -B 3 3
01:10:34 AM pgpgin/s pgpgout/s fault/s majflt/s pgfree/s pgscank/s
pgscand/s pgsteal/s %vmeff
The important stats are majflts/s, which means that pages had to be read
from disk and pgsteal/s, which denotes the number of the modified pages
backed up and reclaimed as "free". In this context "free" doesn't mean
empty, the page being free means that the page has a valid backup. Page
stealing definitel and paging out (pgpgout/s) definitely means that
there is a memory problem. On Red Hat systems, sar is available in the
sysstat package. Another good indication that something is wrong is
large proportion of kernel mode cpu time, as shown by top. Also, "top"
is a good indicator because it shows the swap usage. If the swap usage
keeps growing, there is a trouble with memory.
Regards
On 12/5/18 7:44 PM, kyle Hailey wrote:
Linux 4.15.0-42-generic (umajor) 12/06/2018 _x86_64_ (8 CPU)
01:10:37 AM 23049.33 3421.33 16.00 0.00 81.33 0.00
0.00 0.00 0.00
01:10:40 AM 19186.67 1.33 102.67 0.00 116.00
0.00 0.00 0.00 0.00
01:10:43 AM 14.67 5064.00 32142.67 0.00 25249.00
0.00 0.00 0.00 0.00
Average: 14083.56 2828.89 10753.78 0.00 8482.11
> One of those questions that seems like it should have been nailed down
> 20 years ago but it still seems lack a clear answer
>
> How do you detect memory issues ?
>
> I always used "*_po" or "paged outs_*". Now on Amazon Linux I don't
> see "po" but there is "bo" (blocks written out). In past, at least on
> OSF & Ultrix, page outs were a sign of needed memory that was written
> out to disk and when I needed that memory it would take a big
> performance hit to read it in. Thus "po" was a good canary on the coal
> mine. Any consistent values over over say 10 were a sign.
>
> Some people use "*_scan rate_*" but I never found that as easy to
> interpret as page outs. Again what values would you use
>
> Some suggest using freeable memory as a yardstick where freeable is
> "free" + "cached" or MemFree + Cached + Inactive. Even in this case
> what would you use for values to alert on?
>
> I've always ignored swap stats as if you are swapping it is too late.
>
> What do you use to detect memory issues ?
>
> Kyle
-- Mladen Gogala Database Consultant Tel: (347) 321-1217 -- http://www.freelists.org/webpage/oracle-lReceived on Thu Dec 06 2018 - 07:26:50 CET