Other methos to srite log

I want to mentain a error log for my application.

Presently we are using text file for writing log.

We can not use database for writing log as error/log may be related to database.
I don't want to use event log. Because considering client server application it will write it on client & I want my log on central place.

My problem is Because of text file log I am not able to filter my log.

Is there any solution for this.

How much performarmace will get effected if I write this log in xml format.

How to write in xml format?

if anybody has different solution to this pls let me know.