Updatable views using the 'INSTEAD OF' trigger

All views are not updatable in a database - especially if the underlying query is a complex one. This article gives interesting examples of the challenges faced in updating views.

But latest versions of databases, support a INSTEAD OF trigger, that enables us to make all views updatable. INSTEAD OF triggers fire in place of the triggering action.

The links below show how the 'INSTEAD OF' trigger can be used in different databases:

Oracle: http://www.psoug.org/reference/instead_of_trigger.html

DB: http://www-128.ibm.com/developerworks/db2/library/

techarticle/0210rielau/0210rielau.html

SQLServer: http://msdn.microsoft.com/en-us/magazine/cc164047.aspx 

Cold start Vs Warm start of programs

We often notice that if we start a Windows Forms application the first time after a system reboot, then the start-up time is quite long. But if I close and open the win-form application again, then the application start-up time is reduced drastically. This is true for all programs - Java. .NET, VB... not just WinForms. 

For e.g. open a 5 MB word doc right after reboot and then reopen it again. There would be a difference of 5x-10x in startup times.  This difference between start-up times is called as Cold start and Warm start.

This happens because of 'disk-cache'. The 'disk-cache' is part of RAM that is dedicated to caching disk pages into memory. So the next time, a program is accessed, the disk cache is hit first and if the required program is found there, then it is loaded into the program space. Hence expensive disk access is eliminated and hence the start-up time is much faster. The pages remain in disk cache as long as possible and are removed based on a FIFO principle.

Operating systems have started using this technique to make programs appear faster. 

For example superfetch service on windows vista (xp has prefetch) does this by putting your most frequent used applications into the ram, so when you launch them, they are actually launched not for the first, but second time. 

Disabling startup programs

In Windows XP, if you are getting annoyed by the number of programs that start-up when the OS loads, then there is an easy way to disable the programs we don't need.

Just type "msconfig" in the 'Run' window.  A window titled 'System Configuration Utility' would come up. Navigate to the 'StartUp' tab and uncheck those programs that need not be started at boot time.