RE: How do you detect memory issues ?

2 cents  

I have always alerted off swapping using memstats values. I have store vmstat because sar was not always installed or available without request and that was not always possible given the nature of many unix admins. If I did notice paging I don’t think it ever resulted in any issues until swapping started to be a threat. Swap is a hard threshold and “soft” (one that only alerts if over X for a certain time).  

From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of kyle Hailey Sent: Thursday, December 6, 2018 1:36 PM To: Mladen Gogala <gogala.mladen_at_gmail.com> Cc: ORACLE-L <oracle-l_at_freelists.org> Subject: Re: How do you detect memory issues ?    

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 <mailto: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  

 

 

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



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