Re: How do you detect memory issues ?

nmon is indeed a great tool.

it is much better when used in conjunction with the analyzer

http://www.ibm.com/developerworks/aix/library/au-nmon_analyser/index.html

On Thu, Dec 6, 2018 at 19:16 Mladen Gogala <gogala.mladen_at_gmail.com> wrote:

> Another very decent monitoring tool is Nigel's monitor, also known as
> "nmon". Those who have worked on AIX are probably well acquainted with that
> tool. It also works on both Red Hat and Ubuntu. Here is a sample:
>
> This utility probably works on Amazon Linux, too.
>
> Regards
>
>
> On 12/6/18 2:36 PM, kyle Hailey wrote:
>
>
> Thanks Mladen
> "sar -B" works on Amazon Linux
> and it still amazes me how non-obvious monitoring memory pressure is to
> this day
>
>
>
> On Wed, Dec 5, 2018 at 10:28 PM Mladen Gogala <gogala.mladen_at_gmail.com>
> wrote:
>
>> 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
>> Linux 4.15.0-42-generic (umajor) 12/06/2018 _x86_64_ (8 CPU)
>>
>> 01:10:34 AM pgpgin/s pgpgout/s fault/s majflt/s pgfree/s pgscank/s
>> pgscand/s pgsteal/s %vmeff
>> 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
>>
>>
>>
>> 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:
>>
>> 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
>>
>> --
> Mladen Gogala
> Database Consultant
> Tel: (347) 321-1217
>
> --
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist Principal Consultant at Pythian
Pythian Blog http://www.pythian.com/blog/author/still/ Github: https://github.com/jkstill

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