Hey Subhadip. I don't know how this question managed to end up in the general forum, but I'll just move it later once I figure out who can do it.
Parsing through the backgrounder log files is not really a solution I would recommend for this need. The same information can be found in a much more structured and consistent fashion in the PostgreSQL database that Tableau Server uses to store information in. You can read about how to make the data in it available for reporting using these two links (in this order):
The table you will want in that database is called "background_jobs", but I would recommend using a pre-built connection, like this datasource I built for gleaning this information:
Once you have the data you need in a Tableau Workbook, my preferred solution for building an alert off of it is to use VizAlerts , as Toby suggested. That solution will work for what you are trying to do, but there are some steps required to set it up. If this is something you are interested in, let me know when you've got your data in a workbook and have VizAlerts set up on your server, and I can assist in building your alert.
I would like to know how to enable email alerts for extract refresh failures using VIZALERTS. I have installed VIZALERTS but need to know what are the other steps involved in it.