[Nix-dev] Please test Nix store auto-optimise

[Vladimír Čunát]

Hi again.

TL;DR: on a slow HDD the slow-down can be noticeable, especially for 
large packages with lots of files.

On 02/12/2015 11:47 AM, Wout Mertens wrote:
> Disadvantages:
> - Need to checksum all files written to the store
>    * this is fast while writing the files because they still are in cache

I'm using the option for some time now on my slowly-rotating HDD with 
Btrfs. From the start I noticed that if lots of packages are just 
fetched from the binary cache, then the HDD is much bigger bottleneck 
than before. Today I hit an especially large one when testing 
opencascade - it worked for many minutes just writing the package into 
the store before I killed it - it's probably because the package is both 
large and has lots of files (~800 MB in ~62k files), so it likely didn't 
fit all into the cache while I was working on other things. It was built 
on another machine connected by a fast ethernet, so the problem was just 
the deduplication part (network was idle most of the time).

On an SSD the choice is much clearer of course, as they're both much 
faster to seek and smaller (in a comparable price range).


Vladimir


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