[squid-users] squid doesn't cache objects in memory when using SMP and shared memory cache

Alex Rousskov rousskov at measurement-factory.com
Mon Jan 15 18:57:26 UTC 2018

On 01/15/2018 08:22 AM, Amos Jeffries wrote:

> AIUI, SMP-mode rock operates as a fully separate process (a "Disker" 
> kid) which delivers its results as objects already in shared memory
> to the worker process.

Yes, disk hits are delivered to workers via shared memory, but...

> There should be little or no gain from that promotion process anymore -

I disagree: A disk hit is still a lot slower than a memory hit because a
disk hit involves reading from a disk, which is a major performance

The shared memory pages used to deliver disk hits to workers are then
reused for delivering other disk hits. Those pages are not a part of a
cache. Ideally, those pages could be added to (swapped with) the memory
cache pages (to avoid memory copying; when other conditions are met),
but Squid does not have the code to do that yet. We do not even have the
code to serve hits from shared memory -- we copy the bytes from shared
to local memory first.


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