[Gluster-users] quick-read vs. io-cache - was Re: mod_glusterfs?

Ian Rogers ian.rogers at contactclean.com
Wed Mar 24 17:38:25 UTC 2010

On 23/03/2010 18:40, Raghavendra G wrote:
> On Tue, Mar 23, 2010 at 5:05 PM, Ian Rogers 
> <ian.rogers at contactclean.com <mailto:ian.rogers at contactclean.com>> wrote:
>     Yes I know, I reported that bug :-)
>     If you're using io-cache then quick-read seems irrelevant as
>     io-cache has 128K pages internally.
> io-cache and quick-read perform different functions. Normally while 
> reading a file, glusterfs (fuse) get following calls from VFS,
> lookup,
> open,
> read,
> .
> .
> .
> read,
> flush,
> close.
> But quick-read exploits an internal feature of glusterfs present in 
> lookup to get the entire file in lookup call itself. Hence open, read 
> and close calls are short-cut at quick-read itself and they don't 
> reach server thereby saving 3 transactions over network (probably more 
> due to read).

Is it possible for io-cache to detect if a file is smaller than the 
internal page size (or whatever the cut-off is) and then use the 
quick-read shortcut itself?

In a LAMP situation I'd be wanting to use io-cache but there's also a 
lot of small files. Having both io-cache and the quick-read cache would 
just mean the files are double cached - using up twice the memory needed 
as well as an extra set of memory copies to shuffle things around.

Because of this, and the no-total-size-limit bug in quick-read, I'd 
quite like quick-read to be deprecated and it's functionality added to 
io-cache rather than fixing the memory limit bug in quick-read.



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