CSS Fixed, Static Position Toggle
By Steph Skardal
September 9, 2011
In a recent Rails project, I had to implement a simple but nifty CSS trick. A request came in to give a DOM element fixed positioning, meaning as the user navigates throughout the page, the DOM element stays in one place while the rest of the page updates. This is pretty common behavior for menu bars that show up along one of the borders of a window while a user navigates throughout the site. However, this situation was a bit trickier because the menu bar that needed fixed positioning was already a few hundred pixels down the page below header and navigation content:
I came up with a nifty way of using jQuery to toggle the menu bar CSS between fixed and static positioning. The code uses jQuery’s scroll event handler to adjust the CSS position setting of the menu bar as users scroll through the page. If the window scroll position is below it’s original top offset, the menu has fixed positioning at the top of the window. If the window scroll position is above it’s original top offset, the menu has static positioning. Here’s what the code looks like:
var head_offset = jQuery('#fixed_header').offset();
jQuery(window).scroll(function() {
if(jQuery(window).scrollTop() < …css javascript jquery
Postgres Open: One week to go!
By Josh Williams
September 7, 2011
Wow, time flies, Postgres Open is almost upon us!
I’ll be there giving a talk Thursday morning on monitoring tools and techniques, and possibly helping with the Bucardo 5 replication session Friday afternoon. Sadly I’ll need need to catch a flight shortly after that, so there won’t be much time to explore Chicago around everything going on. But at least it’ll be nice to get out to a conference again!
conference postgres
SQL errors in Interchange
By Jeff Boes
September 7, 2011
Interchange has a little feature whereby errors in a [query] tag are reported back to the session just like form validation errors. That is, given the intentional syntax error here:
[query ... sql="select 1 from foo where 1="]
Interchange will paste the error from your database in
$Session->{errors}{'table foo'}
That’s great, but it comes with a price: now you have a potential for a page with SQL in it, which site security services like McAfee will flag as “SQL injection failures”. Sometimes you just don’t want your SQL failures plastered all over for the world to see.
Simple solution:
DatabaseDefault LOG_SESSION_ERROR 0
in your Interchange configuration file, possibly constrained so it only affects production (because you’d love to see your SQL errors when you are testing, right?).
interchange sql
Ruby on Rails Performance Overview
By Steph Skardal
September 6, 2011
Over the last few months, I’ve been involved in a Ruby on Rails (version 2.3) project that had a strong need to implement performance improvements using various methods. Here, I’ll summarize some the methods and tools used for performance optimization on this application.
Fragment Caching
Before I started on the project, there was already a significant amount of fragment caching in use throughout the site. In it’s most basic form, fragment caching wraps a cache method around existing view code:
<%= cache "product-meta-#{product.id}" %>
#insert view code
<% end %>
And Rails Sweepers are used to clear the cached fragments, which looks something like the code shown below. In our application, the Sweeper attaches cache clearing methods to object callbacks, such as after_save, after_create, before_update.
class ProductSweeper < ActionController::Caching::Sweeper
observe Product
def after_save(record)
expire_fragment "product-meta-#{product.id}"
end
end
Fragment caching is a good way to reuse small modular view components throughout the site. In this application, fragment caches tended to contain object meta data that was shown on various index …
performance ruby rails
Bucardo PostgreSQL replication to other tables with customname
By Greg Sabino Mullane
September 5, 2011
Image by Flickr user Soggydan
(Don’t miss the Bucardo5 talk at Postgres Open in Chicago)
Work on the next major version of Bucardo is wrapping up (version 5 is now in beta), and two new features have been added to this major version. The first, called customname, allows you to replicate to a table with a different name. This has been a feature people have been asking for a long time, and even allows you to replicate between differently named Postgres schemas. The second option, called customcols, allows you replicate to different columns on the target: not only a subset, but different column names (and types), as well as other neat tricks.
The “customname” options allows changing of the table name for one or more targets. Bucardo replicates tables from the source databases to the target databases, and all tables must have the same name and schema everywhere. With the customname feature, you can change the target table names, either globally, per database, or per sync.
We’ll go through a full example here, using a stock 64-bit RedHat 6.1 EC2 box (ami-5e837b37). I find EC2 a great testing platform—not only can you try different operating systems and architectures, but …
bucardo cloud database postgres
Building Xpdf on Ubuntu
By Jon Jensen
August 31, 2011
It may happen that you need to use Xpdf, even though it no longer ships with Ubuntu and is considered … outdated? buggy? insecure? In any case, it still renders some PDFs that Poppler-based viewers such as Evince don’t, or allows some troublesome PDFs to print as fonts and line art instead of a rasterized mess.
Here’s how I built and installed xpdf 3.02 on Ubuntu 11.04 (Natty Narwhal) x86_64:
sudo apt-get install libfreetype6-dev libmotif-dev
wget ftp://ftp.foolabs.com/pub/xpdf/xpdf-3.02.tar.gz # now 3.03 is current
tar xzpf xpdf-3.02.tar.gz
cd xpdf-3.02
./configure --with-freetype2-library=/usr/lib/x86_64-linux-gnu \
--with-freetype2-includes=/usr/include/freetype2 \
--with-Xm-library=/usr/lib \
--with-Xm-includes=/usr/include/Xm
make
# see lots of warnings!
sudo make install
That’s it. Not as nice as the old native Debian/Ubuntu packages, but gets the job done.
graphics open-source tips ubuntu pdf
Giraffes and Liquid Galaxy
By Josh Tolley
August 25, 2011
We build lots and lots of Google Earth tours, typically for use with a Liquid Galaxy. These tours tell Google Earth to start at one point and fly to another, displaying various images along the way. They’re written in an XML-based language called Keyhole Markup Language, or KML. Various KML elements describe points on the globe, 3D objects, tracks through space, or other items, and a series of Google-specific KML extensions can define an automated tour in which Google Earth flies through these objects.
Now for a bit of dogma: writing large volumes of XML by hand is a drag. Writing KML is no exception. So when I started building KML tours, I was keen to build or find tools to make it easier. For my first KML project, making a tour through each End Point employee’s home city, I built a Perl script to convert a file of employee data to KML. This worked well enough, but I soon learned typing out all the KML was just half the pain. The other half was adjusting camera paths, camera angles, timing, and all sorts of other little things. Unfortunately all these adjustments had to be done by trial and error, and all by hand. Getting Google Earth’s camera to circle a particular point, for …
google-earth visionport kamelopard kml
PostgreSQL log analysis / PGSI
By Greg Sabino Mullane
August 19, 2011
Image by “exfordy” on Flickr
End Point recently started working with a new client (a startup in stealth mode, cannot name names, etc.) who is using PostgreSQL because of the great success some of the people starting the company have had with Postgres in previous companies. One of the things we recommend to our clients is a regular look at the database to see where the bottlenecks are. A good way to do this is by analyzing the logs. The two main tools for doing so are PGSI (Postgres System Impact) and pgfouine. We prefer PGSI for a few reasons: the output is better, it considers more factors, and it does not require you to munge your log_line_prefix setting quite as badly.
Both programs work basically the same: given a large number of log lines from Postgres, normalize the queries, see how long they took, and produce some pretty output.If you only want to look at the longest queries, it’s usually enough to set your log_min_duration_statement to something sane (such as 200), and then run a daily tail_n_mail job against it. This is what we are doing with this client, and it sends a daily report that looks like this:
Date: Mon Aug 29 11:22:33 2011 UTC
Host: acme-postgres-1
Minimum …analytics database monitoring performance postgres