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Showing posts from January, 2012

SVN Revert (but only *some* changes)

Sometimes I endeavor in complicate refactorings and, instead of commiting to a branch when at least a part is working, I keep editing until I lose control of the source and wished that I could go back to that previous working situation.

The solution is, luckily, not too difficult:

save the edits to a patch
svn diff > great_mother_of_all_patches.patchrevert the project to the last commit:
svn revert -R .apply the patch edit by edit (I know this is tedious) using the eclipse "Team Synchronizing" perspective, then click on the Synchronize button and choose the Synchronize with patch optionDisclaimer: I don't use the Eclipse subversion plugin because, on Linux at least, it frequently crashes Eclipse.

OTRS-hacking: log all sql queries for use in external reports

OTRS is a great ticket-tracking/helpdesk software. It even has cool statistics built in, but sometimes the PHB goes crazy and asks for impossibily detailed statistics.

For those situations when the stats module cannot help us there a couple of (Open Source) tricks up our sleeve:
install the Eclipse Birt web reporting application (we will need java and tomcat for that)create a custom report using the report designer deploy the report on the server and send the link to the boss To make sure the SQL queries used in the report are the same used by OTRS we can temporarily have OTRS log all queries (remember to disable logging after you're done or your log files will grow out of control) by editing the Kernel/System/DB.pm file as documented here:

# 0=off; 1=updates; 2=+selects; 3=+Connects; # $Self->{Debug} = $Param{Debug} || 0; # leave the original around for later $Self->{Debug} = 2;

Grails, blobs and postgres 'bytea_output'

Grails has great support for storing binary data into any database, Postgres included. It is usually simple to use but today it gave me problems.

I have an application originally developed on pg 8.4 and grails 1.3.6 which stores images in a database table and used to work fine until I upgraded the database to 9.1. It turns out that with version 9 Postgres by default will return data to the client using a new hex format, instead of the escape format used in versions < 9. This, of course, confuses the client which returns garbage to the browser, hence the corrupted image.

The solution is, luckily, quite simple: just tell postgres to revert to the old behaviour. It seems that this behaviour can be tuned per database, so you could have one database using the new format and another the old one:

ALTER DATABASE dbname SET bytea_output='escape';
I should point out that I could also have updated the jdbc driver (now I'm using postgresql-8.3-603.jdbc3.jar), but that seems more ri…

Using SQLite to keep state in shell scripts

Bash shell scripting is one the things that I miss more on the times I work on Windows. Even as good as shell scripting is, sometimes I wish it was easy to keep track of state across script executions, for instance when a script executes a rsync at short intervals. In that case I don't care if one particula rsync fails, but I definitely care if it fails, say, ten times in a row or for more than a day.

To do this I need some kind of way to keep state and record each run exit status. The simplest approach that I could think of is to use SQLite. Copied straight from the SQLite site: SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.


As I said, in this example I'll show how to track the status of a series of rsync operations, all run from a central node and pushed to remote nodes. The…

Rsync (or any other cygwin daemon) as a Windows service

Today I was asked to quickly put together a script to replicate files/directories from a central server to a number of XP clients. This would be dead simple if it was not for Windows.
The customer originally thought of robocopy/xcopy but I dont' really trust them: error reporting is kinda difficult to read and copying over cifs is slow and unreliable. So I set out to build it on top of rsync, but to do that I had to find a way to get rsync installed as a service on all the clients.

Turns out it's quite easy. I started from a clean cygwin install to which I added rsync and cygrunsrv. The latter is the native cygwin tool that can be use to run any tradition *nix daemon as a native Windows service.
Even a basic install like this will be in the order of 50MB or so which is too large for quick deployments. I then started trimming all the stuff that was not essential to the rsync service.

At the end of the trimming process I was left with a mere 10MB, which after being compressed in…

JTS processing Grails servlet

Sometimes it is convenient to make certain topological operations available in a web-based gis. For a gis that makes heavy use of Javascript (like OpenLayers-based ones) it might be worth looking at jSTS, a Javascript port of JTS.

For all the rest and for those who don't want to load yet another library in the browser you can always write a Grails controller that encapsulates common JTS operations like buffer, intersection, union, etc.
Assuming you are familiar with Grails the steps are as follows: drop the jts jar in the lib directorycreate a controller and define the relevant methodsdefine a url mapping to prettify the calls Step 1 is trivial, so we'll go straight to 2. Create a controller and call it JtsController, then open the source file and paste this code:
import com.vividsolutions.jts.geom.* import com.vividsolutions.jts.io.* import com.vividsolutions.jts.operation.overlay.snap.* import grails.converters.JSON import grails.plugins.springsecurity.Secured @Secured([…

Managing a Mapserver farm with Salt

Mapserver is probably the most popular Open Source web mapping platform (even though Geoserver is getting much of the limelight nowadays).

One of the advantages that Mapserver has against Geoserver is that its configuration is pretty easy because it consists of a flat text file (Geoserver instead uses a xml-backed repository).
Because of this kind of repository managing a Geoserver farm becomes complicated when changes have to be replicated across all hosts and the services restarted to pick up the changes. To address this issue there have been recent efforts to build a multi-master replication mechanism plugged into Geoserver. While this is pretty cool (and it's done by an Italian company of which of course I'm proud of, being an Italian myself) I think it's even cooler to see how easy it is to manage Mapserver configuration files in a similar cluster environment.

The Mapserver setup is as follows:
a cluster of mapserver servers serving WMS through a number of maps (more t…