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From Justin Ross <justin.r...@gmail.com>
Subject Re: Proposal: Replace legacystore with linearstore as the default store for qpid linux builds
Date Wed, 11 Feb 2015 18:57:28 GMT
I concur.  I think it's the right time.

On Wed, Feb 11, 2015 at 11:15 AM, Robbie Gemmell <robbie.gemmell@gmail.com>
wrote:

> This sounds reasonable enough to me. I dont think we really need a
> formal vote on it though, its not a project release or procedural
> issue, and whilst it is a behavioural change its not a major rework
> (sounds like flipping a couple OFF/ON flags?) and isnt going to
> require a much effort for anyone wanting the old behaviour. Putting it
> out for discussion for a while as you have done seems sufficient to
> me, and then proceeding if that discussion doesnt lead us in another
> direction.
>
> Robbie
>
> On 10 February 2015 at 15:52, Kim van der Riet <kim.vdriet@redhat.com>
> wrote:
> > Since qpid began, what is now called legacystore has been the default
> linux
> > store for qpid builds. This is a per-queue circular disk buffer store.
> This
> > store has some management difficulties, the most egregious of which is
> > managing the size of the disk buffer. It is easy for users to undersize
> the
> > buffer, and when it gets full, the store refuses to write further records
> > until more space has been freed up. It is also easy for users to oversize
> > all their queues so as to not run into this problem, and thus wastefully
> > consume disk resources and massively increase the time necessary for
> > recovery.
> >
> > Approximately a year ago work started on a new store called linearstore.
> > This store is forked from legacystore, but the disk buffers are no longer
> > fixed circular. Instead they are open-ended linear buffers, which take
> their
> > files from a common Empty File Pool. As new files are needed, they are
> taken
> > from the EFP and placed on the leading edge of the journal, while empty
> > files are returned to the EFP from the trailing end of the journal. If
> the
> > EFP itself is emptied of files, the store will automatically create new
> > ones. This removes the need for the user to guess at their worst-case
> > scenarios to size a circular buffer.
> >
> > The linearstore also adds the ability to store the journals for
> particular
> > queues on different disk partitions. This allows some queues to use high
> > performance media (such as solid state drives) where necessary, while
> other
> > queues can use regular disks.
> >
> > It is my belief that the linearstore has now progressed to the point
> where
> > it can now replace legacystore as the default store. Currently, both
> stores
> > are represented in the cmake build. However, linearstore defaults to OFF
> > while legacystore defaults to ON. The reason for this is that both stores
> > cannot be present at the same time or the broker will attempt to load
> them
> > both. Only one store at a time can be loaded in the broker, and having
> both
> > results in undefined behavior. I propose to leave legacystore in place
> for
> > the time being, but default the build to OFF, while linearstore will have
> > its default set to ON.
> >
> > If you have any comments or concerns, please make them known. Otherwise
> I'll
> > start a vote on this in a few days.
> >
> > Kim
> >
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>
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