We were writing a new service to distribute financial pricing data around the trading floor as a companion to our new desktop pricing tool. The plugin architecture allowed us to write modular components that could tap into the event streams for various reasons, e.g. provide gateways to 3rd party data streams.
Linking New to Old
One of the first plugins we wrote allowed us to publish pricing data to a much older in-house data service which had been sat running in the server room for some years as part of the contributions system. This meant we could eventually phase that out and switch over to the new platform once we had parity with it.
The plugin was a doddle to write and we quickly had pricing data flowing from the new service out to a test instance of the old service which we intended to leave running in the background for soak testing. As it was an in-house tool there was no installer and my colleague had a copy of the binaries lying around on his machine . Also he was one of the original developers so knew exactly what he was doing to set it up.
A Curious Error Message
Everything seemed to be working fine at first but as the data volumes grew we suddenly noticed that the data feed would eventually hang after a few days. In the beginning we were developing the core of the new service so quickly it was constantly being upgraded but now the pace was slowing down the new service was alive for much longer. Given how mature the old service was we assumed the issue was with the new one. Also there was a curious message in the log for the old service about “an invalid transaction ID” before the feed stopped.
While debugging the new plugin code my colleague remembered that the Transaction ID meant the message sequence number that goes in every message to allow for ordering and re-transmission when running over UDP. The data type for that was a 16-bit unsigned integer so it dawned on us that we had probably messed up handling the wrapping of the Transaction ID.
Use the Source Luke
Given how long ago he last worked on the old service he couldn’t quite remember what the protocol was for resetting the Transaction ID so we decided to go and look at the old service source code to see how it handled it. Despite being at the company for a few years myself this all pre-dated me so I left my colleague to do the rummaging.
Not long after my colleague came back over to my desk and asked if I might know where the source code was. Like so many programmers in a small company I was a part-time sysadmin and generally looked after some of servers we used for development duties, such as the one where our Visual SourceSafe repository lived that contained all the projects we’d ever worked on since I joined.
The VCS Upgrade
When I first started at the company there were only a couple of programmers not working on the mainframe and they wrote their own version control system. It was very Heath Robinson and used exclusive file locks to side-step the problem of concurrent changes. Having been used to a few VCS tools by then such as PVCS, Star Versions, and Visual SourceSafe I suggested that we move to a 3rd party VCS product as we needed more optimistic concurrency controls as more people were going to join the team. Given the MSDN licenses we already had along with my own experience Visual SourceSafe (VSS) seemed like a natural choice back then .
Around the same time the existing development server was getting a bit long in the tooth so the company forked out for a brand new server and so I set-up the new VSS repository on that and all my code went in there along with all the subsequent projects we started. None of the people that joined after me ever touched any of the old codebase or VCS as it was so mature it hadn’t needed changing in some time and anyway the two original devs where still there to look after it.
The Office Move
A couple of years after I joined, the owners of the lovely building the company had been renting for the last few decades decided they wanted to gut and renovate it as the area in London where we were based was getting a big makeover. Hence we were forced to move to new premises about half a mile away. The new premises were nice and modern and I no longer had the vent from the portable air-conditioning machine from one of the small server rooms pumping out hot air right behind my desk .
When moving day came I made sure the new server with all our stuff on got safely transported to the new office’s server room so that we ready to go again on Monday morning. As we stood staring around the empty office floor my colleague pointed to the old development server which had lay dormant in the corner and asked me (rhetorically) whether we should even bother taking it with us. As far as I was concerned everything I’d ever needed had always been on the new server and so I didn’t know what was left that we’d still need.
My colleague agreed and so we left the server to be chucked in the skip when the bulldozers came.
Dormant, But Not Redundant
It turned out their original home-grown version control system had a few projects in it, including the old data service. Luckily one of the original developers who worked on the contributions side still had an up-to-date copy of that and my colleague found a local copy of the code for one of the other services but had no idea how up-to-date it was. Sadly nobody had even a partial copy of the source to the data service we were interested in but we were going to replace that anyway so in the end the loss was far less significant than we originally feared.
In retrospect I can’t believe we didn’t even just take the hard disk with us. The server was a classic tower so took up a far bit of room which was still somewhat at a premium in the new office whereas the disk could probably have sit in a desk drawer or even been fitted as an extra drive in the new midi sized development server.
 There are a lot of stories of file corruption issues with VSS but in the 7 years I’d used it with small teams, even over a VPN, we only had one file corruption issue that we quickly restored from a backup.
 We were on the opposite side from the windows too so didn’t even get a cool breeze from those either.