Since ASP.NET 2.0 I’ve always liked the accessible way that caching has been presented to the ASP.NET developer. There are a number of good options for improving your server performance through server caches that are all really easy to get your head around and simple to implement in their most basic form.
Digging deeper into the cache
Like with most aspects of development when one looks more closely find it can get much more complex in order to optimise caching to your particular site heuristics.
The caching on the ecommerce site I’m working on at the moment was mostly removed during a site revamp last year, with the intention to put it back in again. Some of the new features I’m writing at the moment would be hit hard after a monthly email shot, thus caching is very attractive for these pages. Thus I ended up reminding myself of my options.
The site has a grid containing up to a thousand products and prices to show to the site visitor. The view of these items had to have the following features;
- Ability to sort the grid
- May filter the items viewed
- Can page the results with variable items per page
- Items in grid take context of current user language and currency selection
Page caching is not really helpful, instead I’m best caching the IEnumerable class that represents the items in the grid.
Watch out for bad performance behaviour
The thing you have to remember about web pages is that multiple users may be accessing the same page at the same time. This means you have to be a bit defensive about how you cache the object. I know the object take a long time to build as it comes from a database query that is quite intensive and some post query processing that takes a bit of time too, thus it is very realistic to see that if three users hit the page in quick succession when the cache is empty, they will all see it as empty and all simultaneously try to populate the cache, overwriting each other as they reach completion and write to the cache. Obviously this is going to load the application and database unnecessarily.
Reading around the subject I found the good old singleton pattern is a good one to start of using. If you’ve been through the joy of multithreaded applications you will know about Lock or SyncLock in vb. This allows you to lock a section of code so that only one thread may be running that section at any time. The other threads are blocked indefinitely waiting for the lock to clear. Well if you use a lock on the cache refresh, obviously the other users hitting the page will have to wait for the cache to be refreshed until they can move on and read from it.
The other one to watch out for out there that I noticed while reading up was many code examples for using the cache that forget that the item may drop out of the cache at any moment. So if you check the object exists in the cache, you need to grab it at the same time as next time you go to fetch it, it may have dropped out and nothing will be returned.
Got the cache working then used LINQ to Objects to get the paging and filtering working, what a joy to do, I’m really getting into LINQ!
Windiff Directory comparison tool, by Mircosoft
It is always great to discover utilities that already exist on your machine.
Yesterday I wanted to compare two directories trees containing thousands of directories to see what had changed between two computers. I was trying to resolve a source control error for a big ASP.NET website.
In this case I was not looking for anything complicated merely what changes there are between the machines. In the past I’ve tried downloads from the internet that are utilities that do all sorts of interesting stuff in comparing files and directories. However I didn’t have any of these installed on the machine I was using. I then uncovered Windiff.exe.
In Microsoft Windows 2000 and later, Windiff.exe is included on the original CD-ROM in the Support\Tools folder details of how to use it can be found here: http://support.microsoft.com/kb/159214 . It is a windows forms driven application that shows in two columns what has changed between the two directories and allows the user to drill down into the files listed to look at the differences within those files too.
The application also allows editing of those file too. Very, very useful. So after going into the vista start>Start Search I typed windiff and was away. Compared the directories, found my missing files and job done.
It happens so rarely that a job ends up simpler that you thought, so its woth blogging about when it happens!
System.Web.UI.UpdatePanelTriggerCollection must have items of type 'System.Web.UI.UpdatePanelTrigger'. 'asp:AsyncPostBackTrigger' is of type 'System.Web.UI.AsyncPostBackTrigger'.
I scratched my head for a little thinking this was something more complicated that it was.
After upgrading a ASP.NET site from ASP.NET 2.0 to the 3.5 framework where the site used a derived AJAX update panel in a separate referenced class library.
<asp:AsyncPostBackTrigger ControlID="albViewMoreCategories" EventName="Click" />
- was the line causing the compilation error.
The website project updated to 3.5 fine and changed the reference to the system.web.extensions class to a 3.5 version. However the associated class library still clung onto the previous 1.0 version of the class.
Removing the system.web.extensions 1.0 and relacing with it with the 3.5 version got rid of the conflict between the two projects.
I hope this helps some one.
Windows Communications Framework (WCF), VB.NET windows forms, SQL server, Oracle, Pindar Catalogue Management System (CMS)
Pindar produce a Catalogue Management System (CMS), that is used by many large catalogue companies to manage, traditionally printed catalogues. Companies such as the large electronic components catalogues and clothes directories.
From a technical perspective, CMS is an Oracle database that holds all the items, prices, page content, layout, pictures, paragraphs, sections, pages, publications and other resources linked to those entities. It handles work flow of the activities that are required to generate catalogue content with authorisation and release concepts, handles multi-lingual translations and the workflow involved in getting that content translated. As you can tell this is an expensive and powerful publication system for the larger catalogue companies.
The Oracle database if fronted by a number of optional components, the most important to us are the CMS manager this is the forms front end to the system and the Quark extensions that allow the pages to be built in Quark and ultimately sent to the printers in postscript files. Essentially the Quark extensions allow the Quark to understand and build the pages from all the elements held in the database, very cool to see. Oh and it works on both Mac and PC, obviously with the publishing heritage.
Many years ago I wrote an application in Delphi in my own time that took content exported from CMS tables into excel and then built HTML pages using this information. It read the page layouts and essentially built the page in HMTL in a similar same way that the Quark extension does it in Quark (all be it the subsection of functions that we utilised). One of the major problems was handling the Quark and Stibo (previous catalogue management system) tags that littered the text returned from CMS.
Things turned direction and I never actually used this application and the folder got stuffed on my shelf for another time.
Getting the text of the catalogue onto our web pages as text rather than PDFs suddenly went to the top of the list when we bought our Google Mini, and the need to feed it with rich content came along. I dusted down the Delphi project stripped out the bits I needed and started on a adventure to build an application that would allow the publication of item groups from CMS to our internet site. This was also was the prefect project to add to my experience of WCF.
The application had to allow the CMS user to see which item group texts had been updated since they were last published to the web and preview those groups then publishing the new version to the internet.
Follow how I used MD5 check sums and last modified dates, and schema validations to ensure the content had changed and was valid by following the project.
Publishing Catalogue Management System to ASPNET