Open Source Computing and GIS in the UK

Part of my fabulous new plans for portable gis (which will be revealed soon-ish) involve including a database replication option. This might or might not work on the USB drive, but it needs to be open source, portable, and connect to postgresql at the very least. I have been looking at a couple of options for this, without a vast amount of success, it has to be said.

The packages that I have tried are: Daffodil Replicator, dbreplicator (a fork of daffodil replicator), Symmetric-DS, and db -connector for Funambol. Of these, daffodil and dbreplicator seem like the best bet as they will attempt to do some conflict resolution (eg when the same record is added/altered in both databases). They are also java-based, so should be nicely configurable. Symmetric-DS works well, but doesn’t do conflict resolution, so that kind of rules it out for me. I don’t really know about db-connector for funambol as the documentation that I found was quite out of date and I didn’t get very far with it.

So, daffodil replicator and dbreplicator…

They are quite easy to set up, although the documentation in both cases assumes rather more end-user knowledge than perhaps they should do. Basically you find an appropriate jdbc jar file for your database, grab log4j.jar from somewhere, and tell daffodilreplicator/dbreplicator where to find it, by setting appropriate paths in batch files. Then you start the publication server and set up the details for your “master” database, and then do the same for the subscription server and the “client” database. Both are clever enough to translate between different database types, such as postgresql and mysql, which in some cases would be really handy.

My difficulty with both flavours of the package came when creating the “subscription”, ie telling the client database where to go find the master database. In neither case have I been able to sucessfully set this up, because of various errors. Weirdly, both flavours of the package give me an error in my log file about the first ever subscription that I tried to set up, despite having reinstalled, deleted everything I could find, and started from scratch several times.

The documentation in both cases hasn’t been good enough to resolve my issues, and neither have the forums. Actually, I’m still waiting on dbreplicator, which seems to be a little more active, so I should give them the benefit of the doubt for a couple of days.

I can see a great need for this kind of setup, assuming I can get around these initial teething troubles. So, my question is, has anyone successfully set up any of these packages on windows (sorry, but it needs to be windows at this stage), or does anyone know of any other packages I should try?

If I do manage to get things sorted I’ll post a detailed how-to…

Due to popular request (well, two people at least have asked) I have created a google group for Portable GIS, for support, enhancement requests, and other such things. At the moment you need to request an invitation to join, as I don’t fancy having to deal with even larger mountains of spam.

You can find it here: http://groups.google.com/group/portable-gis

Enjoy!

Someone (thanks Bruce) has alerted me to a mistake in Portable GIS, which luckily requires a very minor patch- so minor that I am not going to release a new version now and force everyone to download it again, although it will be fixed in the next version. Basically there is a line in the apache config that doesn’t update it’s drive letter because the slashes are the wrong way around.

To fix:

Go into .\usbgis\apps\xampplite\apache\conf\httpd.conf with a text editor and find the line (should be right at the end of the file):

SetEnv PROJ_LIB N:\usbgis\apps\FWTools2.1.0\proj_lib

Where you might have a slightly different drive letter. To fix, change the directions of the slashes in the file path from \ to / and change the drive letter to whatever your current drive letter is, and save the file. Then when you change the drive letter in future and run the xampp setup, it should automatically update.

Thanks for your patience, thanks again to Bruce for pointing it out, and thanks to everyone for downloading it!

I was contacted by someone who has downloaded portable GIS, very sensibly asking for information on the postgresql connection details. When I tried to respond to this person, their email address bounced back with a permanent failure, so I thought I’d better write something here so he doesn’t think I’m not replying!

Now, I was sure that I had included a readme file specific to the postgresql installation, but it looks like the pixies might have eaten it. Anyhow: the very secret local username and password for postgresql on the USB stick are: postgres and grespost. Please take the opportunity to create your own username and password if you are concerned about security. Don’t say I didn’t warn you…

The next version (in a couple of months) will have better documentation- I promise. The trouble is that as every developer knows, creating documentation is the longest part of any project. If I had waited until I had some decent documentation I wouldn’t have released it at all, and believe me I’m glad I did, the reponse has been fabulous. I won’t, however, be including  documentation about how to use the programmes, as the majority of them already have pretty good user manuals online- I will include links to them though. You can hold me to that if you like!