[rabbitmq-discuss] Database Corruption Possibilities

Fri Jun 3 14:10:28 BST 2011

Thanks Alex. That's also something I thought of - creating a transaction log somewhere else and replay that log if rabbit storage gets corrupted.

However wouldn't I have the same the problem if I use a specific queue to push data to another datastore, i.e. if the consumer listening to that queue is not fast enough, messages will accumulate in the queue. If queue data is corrupted shortly after, I will lose messages before my "transaction log writer" see them.

The only way that I can think of is to persist the message to my custom transaction log (MySQL, etc) _on the publisher side_ before message goes into rabbit. In order to guarantee that _all_ messages go in the transaction log, I would have to do this synchronously, i.e. if I can't persist the data in my transaction log, I won't bother pushing that message to rabbit. But this seems to be doing too much on the producer side and will obviously affect producer performance. Other way of achieving this would be to use two phase commits but I don't want to go there...

I will definitely check @jbrisbin's work. That sounds really interesting.

Cheers,
oseymen

From: Alex Lovell-Troy [mailto:alex.lovelltroy at gmail.com]
Sent: 03 June 2011 12:35
To: Ozan Seymen
Cc: rabbitmq-discuss at lists.rabbitmq.com
Subject: Re: [rabbitmq-discuss] Database Corruption Possibilities

There are a handful of approaches to this problem which all seem to follow a similar pattern.  Until there is a way to replace mnesia with a replicable back end, we've all written something on our own that wraps each amqp transaction with a transactional write to the datastore of our choice and.  I've seen this done with MySQL, MongoDB, and riak personally.

@jbrisbin has done some interesting work with implementing a specific queue that sends messages to riak that looks intriguing.  I believe there is also a piece that pushes messages from riak into rabbitmq.

At least, that was the state of the art the last time I looked

Anyone else?

-alex

On Fri, Jun 3, 2011 at 12:21 PM, Ozan Seymen <Ozan.Seymen at tdpg.com<mailto:Ozan.Seymen at tdpg.com>> wrote:
Hi all,

Can someone please explain the scenarios where we might have Rabbit message storage (is it mnesia?) corrupted in a way that it is not recoverable?

In the solution I am working on, I simply cannot afford to lose any messages. In order to secure this, I will:

*         Rely on publisher confirms. This should ensure that broker will always confirm whether it assumed responsibility and persisted the message.

*         Implement durable queues/exchanges.

*         Ack enabled in consumers to prevent losing messages if consumer dies halfway. I will solve the ordering problem on the consumer side.

Even though all of these above prevent message loss in normal conditions, none of them covers the case where data gets corrupted in the broker. There is a window (albeit small) that things might go wrong: broker assumes responsibility (message is in the disk) and before message is sent to the consumer, broker experiences problems which corrupts the storage. If I can't bring the broker up with all data previously persisted, I've lost messages - producer forgot about the message as broker accepts responsibility and consumers have no idea about the message as it hasn't been delivered to it.

Am I a total paranoid that is beyond help? Even so, I would really appreciate any info you guys can share.

Cheers,
oseymen

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