{{Quickfixn}} Recovery Strategies

[Mike Gatny]

On Fri, Sep 25, 2015 at 11:50 AM, Ian Clements <
ian.clements at investmentsoftwareltd.com> wrote:

> If my service crashes (Server fails or unhandled exception) then my queue
> which is in memory gets lost.  When I restore my service I need to load
> these messages back into the queue.
>

One slick way to do this is to leverage FIX protocol resends.  If you make
the msg seq num part of the data you record when a message is successfully
processed, when a crash occurs you can 1) note the last processed seq num,
2) edit the qf/n .seqnums file accordingly, 3) restart your app.  The other
side will resend what you haven't processed.


> If the crash happened during the current FIX session I was tracking which
> SeqNum I had reached in my DB so I figured in the OnCreate method I could
> just retrieve the messages from the message store but it is returning
> nothing which I don’t understand as the store files are still populated.
>

The message store is for messages you sent, not messages you received.
They are stored in case you need to honor a resend request from the other
side.  And hence the method mentioned above.


> If I have done a LogOut (Which clears the store files as the collection
> resets) and I am still processing messages I persist the messages currently
> on the queue to a file which I can then restore – this approach seems to
> work.
>

Yep, you have to go to disk one way or another -- whether it is writing to
your own ad-hoc file, re-reading the qf messages log, writing to a durable
msg queue, writing to a db.  As long as you can avoid blocking too long
during FromApp/OnMessage, any of these can work.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quickfixn.com/pipermail/quickfixn-quickfixn.com/attachments/20150925/506ec5ca/attachment-0002.htm>