[Spread-users] Thrudb - Document Oriented Database Services

Jake Luciani jake at 3.rdrail.net
Tue Nov 6 20:15:35 EST 2007

Hey Alaric,

Thanks for the heads up! I'll have to add the chunking.

I'm using memcached knowing it forgets things BUT since writes happen right
away and since the system can handle errors gracefully I think its a decent

Empirically, I've bombarded the system with gigs of data with no hiccups.


On Nov 6, 2007 7:56 PM, Alaric Snell-Pym <alaric at snell-pym.org.uk> wrote:

> On 6 Nov 2007, at 10:11 pm, Jake Luciani wrote:
> >
> > Instead, a transaction container is created, the document is
> > compressed and stored under that transaction id in memcached and
> > the transaction id is sent. Memcached becomes kind of a network IPC.
> >
> Look out! Memcached, by default, rejects things over 1MB in size. A
> large size for a compressed document, you'd think, until people start
> storing image files ;-) But easily worked around - just store the
> document in chunks named "transaction id:chunk number". And, of
> course, memcached may choose to forget things - it is a cache, after
> all. How do you handle that, out of interest? My system is designed
> for records of only a few KB, so we just send them over spread, so we
> don't have that problem.
> > Each node receives the message and pulls the document from
> > memcached, once all nodes are ready to process they message the
> > transaction origionator and and says its ready to commit or its
> > failed.
> I'm doing something similar for my replicated database project (which
> is, alas, closed source... for now... but if the powers that be
> consent to changing that, I'll announce it here too); a pre-write is
> broadcast and the client then listens for replies from the data
> storage nodes. Each storage node attempts to provisionally perform
> the write, and returns success or failure (where failure is generally
> a unique key collision etc); the client waits until it has a quorate
> number of yesses, without a single no, and then broadcasts a commit
> message if it succeeds (if it fails, the provisional writes time out,
> but there could easily be a fail message)
> > also libevent is used to monitor the spread socket.
> I need to look into that - I wanted things to be able to time out, so
> I wrote a little subprocess that sends a message-per-second heartbeat
> to a special spread group, so that things that wish to time out can
> join that group and then be sure that SP_receive will not block for
> more than a second. I have my nodes perform certain administrative
> tasks once per second, so it's never an unnecessary wakeup call.
> The heartbeat is generated uniquely in a failsafe manner by the
> highest-lexicographically-ordered member of the heartbeat-senders
> group being the one that sends them, and the other heartbeat
> processes just watching heartbeat-senders for a membership change
> that makes THEM the highest-lexicographically-ordered member.
> >
> > -Jake
> >
> --
> Alaric Snell-Pym
> Work: http://www.snell-systems.co.uk/
> Play: http://www.snell-pym.org.uk/alaric/
> Blog: http://www.snell-pym.org.uk/?author=4
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