[Schevo-devel] Re: concurrency and copy-on-write snapshots

[Jesus Cea]

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First of all: Keep in mind that I am NOT a Schevo User.


Matthew Scott wrote:
>> Also, I guess it's a good suggestion that we employ BDB for Schevo, to
>> use it's DB replication feats and stuff... if ever I may be missing
>> some  points, please enlighten me.
> 
> If the BDB backend for Durus that Jesus Cea is working on is compatible
> with how Schevo uses Durus, I can see that as being a definite option
> once we use the latest version of Durus (see
> http://schevo.org/trac/ticket/5)

Well, I'm not aware of any issue that could preclude my backend to be
used in Schevo. Basically, if your system is using Durus, you can "plug"
my backend as-is. The only real issue is garbage collection of cycles
(not done) and that using BerkeleyDB may increase your sysadmin requirement.

> As far as DB replication, I am not so sure that read/write replication
> would be possible simply by using BDB, since there are synchronization
> issues that are probably best left handled at the Schevo level.

I have a private branch of my backend that allows replication, but the
mirrors are "offline". They are only used as backups. Only one of them
can serve clients at a time.

In fact I would like to improve current DURUS to be able to use
master/slave configurations. The battle is tough :) and have other
priorities first. But progressing.

As a more important battle to fight just now, for example, I would like
Durus to be able to do several object fetch at once, if requests come
from different connections. Current Durus only serve a client at once,
and most of the time is lost waiting for the disk and sending the data
to that client. Meanwhile other connections are simply waiting their turn...

- --
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