RE: Epics Archiver Appliance and Network Storage slowdown

["Manoussakis, Adamandios via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Murali,

 

I had some data back from testing, the http post request is asking for about 3000 PVs from the AA which stores about 4500 PVs Total in the LTS.

 

I did the benchmark test to just transfer a single pb file and was getting around 100MB/s, so I do not think it has to do much with the network since the file size for the 3000 PVs is about 40MB only.  I then reduced the request down to about 1200 PVs and it definitely sped up quite a bit around 15 seconds from the 2.5mins it was taking.  Someone mentioned the lookup time for each PV was log(n) or nlog(n) for the AA but then that doesn’t seem like it would impact going from 1200 to 3000 in the POST.

 

I am curious how many PVs you usually request in a single http  when requesting from the AA, is there an upper limit I should stick to?  You mentioned possibly breaking up the requests into smaller chunks. 

 

Thanks

Adam

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Manoussakis, Adamandios via Tech-talk
Sent: Sunday, February 20, 2022 10:44 PM
To: Shankar, Murali <mshankar at slac.stanford.edu>; tech-talk at aps.anl.gov
Subject: RE: Epics Archiver Appliance and Network Storage slowdown

 

Thanks Murali,

 

I will try to run some more tests including the one that was mentioned to make sure the transfer rates look correct.  I cant imagine the local vs NAS on this small of a setup shouldnt be vastly different.  

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Shankar, Murali via Tech-talk
Sent: Thursday, February 17, 2022 12:01 PM
To: tech-talk at aps.anl.gov
Subject: Re: Epics Archiver Appliance and Network Storage slowdown

 

>> I think for this experiment its only 6000 PVs

I think that should not take this long. Will look into this a bit here as well.

 

Regards,

Murali

 

 

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From: Shankar, Murali
Sent: Saturday, February 12, 2022 8:03 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Epics Archiver Appliance and Network Storage slowdown

 

>> We are using the getDataAtTime endpoint

>> 40MB file from the archive

 

By this I'd guess that you are getting data for several 100,000's of PVs? The getDataAtTime API call has to look at all these 100,000 files ( with perhaps cache-misses for most of them ) and then do binary search to determine the data point. Your NAS needs to support quite a high rate of IOPS to for this to come back quickly. And this is a usecase where even the smallest latency tends to accumulate quickly. Perhaps you can consider breaking down your request into smaller chunks when using the NAS? 

 

Regards,

Murali