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From "Lerner, Steve" <>
Subject RE: proxy.config.cache.ram_cache.size query from eBay
Date Fri, 21 Nov 2014 16:31:10 GMT
Thanks for the tips- right now with avg object size set to 32K and RAM set to 64G its running
very nicely… with 1% of the traffic we are interested in (we have to keep in test until
after retail season) we get 5% cache hit rate.
We’ll try ramping up traffic in January after the retail season and then things will get
interesting. I’ll report in with our stats as we ramp up. We have 2x clusters at 11 machines
each with URLS striped across all 22 with URL hashing.


Steve Lerner | Sr. Member of Technical Staff, Network Engineering | M 212 495 9212 |<>
| Skype: steve.lerner
[Description: logo]

From: Phil Sorber []
Sent: Thursday, November 20, 2014 9:11 PM
Subject: Re: proxy.config.cache.ram_cache.size query from eBay

On Sat Nov 15 2014 at 2:23:13 PM Lerner, Steve <<>>

Thanks for the response. What we are going for here is gazillions of tiny images- 76KB average

We’ll try tweaking average object size… what we’d love to do is just have ATS read from
disk only and have minimal to zero RAM at all… with no swapping of course ☺
If you want, you can set that RAM cache size setting to 0 to disable it. I think you will
see a noticeable slowdown though, unless your RAM cache has a 0% CHR.

You will still have memory usage from the directory and other objects, however.

Old school CDN style- our object library is so massive that this would work for us- and as
we all know its better to serve from disk closer to user than to go over network back to origin.


Steve Lerner | Sr. Member of Technical Staff, Network Engineering | M 212 495 9212 |<>
| Skype: steve.lerner
[Description: logo]

From: Leif Hedstrom []
Sent: Saturday, November 15, 2014 12:10 PM

Subject: Re: proxy.config.cache.ram_cache.size query from eBay

On Nov 13, 2014, at 4:40 PM, Lerner, Steve <<>>
Hi gang- Phil Sorber referred me to this list.

We are setting up clusters of Apache Traffic Server to beef up the front end of our image
services which are… large in terms of volume… to say the least.
We hope to be the big users of ATS and be a strong reference customer- so any help with is
Our first test cluster consistes of 23 machines, ubuntu12.04, Intel(R) 2x Xeon(R) CPU E5-2670
v2 @ 2.50GHz, 128G ram, 95T disk

That is a lot of disk :) With default settings, you would consume roughly 110GB of RAM just
for the indices. The calculation is

   (95*10^12 / 8000) * 10

Take comfort that with squid, you would use 10x as much (128 bytes per index entry). But you
have three options:

1) increase the records.config setting for average object size. That is the 8000 number above.
Doing so means you can store fewer objects in the cache.

2) buy more RAM

3) reduce disk capacity on each box

I thought we had a wiki entry on this subject?


-- Leif

Here is our query:

We are setting records.config as: CONFIG proxy.config.cache.ram_cache.size INT 64G

But we find that trafficserver ignores this limit and grows at the default rate of 1MB RAM
/ 1GB disk.

Example of a current process:

traffic_line -r proxy.config.cache.ram_cache.size returns 68,719,476,736
Which is about 64GB- correct!

But looking at the process:

86050 nobody    20   0  108g 102g 4912 S   54 81.3   1523:33 /ebay/local/trafficserver/bin/traffic_server
-M --httpport 80:fd=7

So basically we’ve set the process to only consume 64GB but its consuming 108GB…

Does anyone have any ideas on why this happens or a way to fix it?
We want to have constrained RAM but tons of disk- we’d much rather have the cache serve
from disk then start swapping RAM

Thanks in advance,


Steve Lerner | Sr. Member of Technical Staff, Network Engineering | M 212 495 9212 |<>
| Skype: steve.lerner

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