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Re: Re: Metrics to calculate 'best' values for cache_mem and cache_dir?
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On 28.03.2012 08:37, babajaga wrote:
I've read (for Linux at least) aufs is superior to diskd,<I have my doubts. First of all, it might depend upon the version of Squidyou want to use.I use 2.7, and, looking at the source code for aufs, ony reads are async. Having some discussion with Amos already regarding this issue, he stated,that async writes were not enabled because being "unstable".Might be different in other versions, though, but, to be shure, it needschecking the source code, because it is a conditional compile (ref.: store_asyncufs.h).And, in case only reads are async, then it needs further verification,whether diskd or aufs should be faster.Because according to my first glance at the code for diskd, diskd does asyncwrites by default.Most likely, diskd has more overhead. But, in case of low hit rate for the cache, I suspects, the performance gains because of async writes might putdiskd into favour.
diskd/ufs/aufs have roughly the same code from squid-2.6 to current stables. Based on Adrians research in 2.7 we _think_ the AUFS problem on BSD is that AUFS write operations involve blocking operations, which Linux kernel implementation evade in the background but BSD hits head on. There are architectural differences in squid-3.x which may come into play but are not expected to unless the bug info is wrong.
Actually, I am checking this issue myself for my own stressed squid, runningalready in production (LINUX, too).In case, the "writing" considers aufs to be generally faster than diskd, itlooks like, it is ignoring the risk of "unstable" write ops.
Thank you. Are you able to post the particulars of this research how it was measured, with what versions and what outcome please? this info could be of help to a lot of people.
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