This is a work-around to this Idea: http://community.tableau.com/ideas/2657
This allows the Tableau administrator to kill a Background Task on the Tableau Server by ending the associated process in the Windows Task Manager. This comes in particularly useful if an extract needs to be stopped without having to restart the Server
1) From the Tableau Admin panel, go to the Background Tasks report.
2) Hover over the mark for the desired Task running (#1 in the below image).
3) In the tool tip that appears, get the number from the Backgrounder ID (#2 in the below image). In the below example the value for the Backgrounder ID is "localhost:2", thus "2" is the value we will use.
4) Now open the Windows Task Manager.
5) Click on the Processes tab.
If you don't have the Command Line column visible then display it. Here's how:
5a) Click on View >> Select Columns...
5b) Select the Command Line box then click the OK button:
5c) You'll now have the Command Line column and you can drag it where you want:
6) Sort the image name (click on the column header to toggle the sorting of the column).
7) Expand the Command Line column and go to the end of it for the "backgrounder.exe" image names:
The number that is in the red box above is the localhost number. Look at the "...hs_err-#_pid..." piece of the command where the # is the backgrounder ID number. I have three backgrounders so their backgrounder IDs are 0, 1, & 2.
8) From step #2 the Backgrounder ID ended with "2" so from the above image I select the top task in the Task Manager (the blue row already highlighted) because the Command Line has a number two in the "...ht_err-2_pid..." piece of the command.
9) Right-click on the highlighted row and select End Process OR click on the End Process button:
9a) If prompted, confirm that you do want to end the process.
10) Windows will kill the process and it will disappear. In a couple seconds Tableau will look annoyingly at you and restart the process. This is perfectly normal and expected.
11) Typically in a few seconds the Tableau Background Task will be killed:
I've notice that sometimes this can take up to a minute to register in the viz; just keep clicking the Refresh every few 5-10 seconds and it will change from In Progress to Error. Tableau does a good job at cleaning up the process to avoid memory leaks.
Your Humble Tableau Server Padawan,
P.S. For versions higher than 8.x (e.g. 9.x) please see Stopping a 9.x Tableau Server Background Task (Windows)