Required Features

Sep 4, 2009 at 11:56 AM

When I attempt to activate the BLOB Cache Farm Flush feature I get the following message:

One or more features must be turned on before this feature can be activated.

On what other features does the BLOB Cache Farm Flush depend?

Sep 4, 2009 at 2:04 PM


The BLOB Cache Farm Flush Feature is designed to operate with publishing sites (that is, site collections on which the "Office SharePoint Server Publishing Infrastructure" is active).  Without the publishing infrastructure active, the BLOB cache isn't (normally) engaged and the Feature wouldn't be of any use.

My guess is that that the publishing infrastructure isn't an active Feature on the site collection you're targeting.  Is this the case?

Sep 4, 2009 at 3:09 PM
Edited Sep 4, 2009 at 3:12 PM


The Office SharePoint Server Publishing Infrastructure feature is active on the target site collection.   The  only inactive out-of-the-box feature is the three-state workflow.

Another thought: Are there any Service Pack level dependencies?  SP2 has not yet been installed on my farm.

Sep 4, 2009 at 3:28 PM


Gotcha! Sounds like things are covered at the site collection level then.  That's normally where an activation dependency problem occurs, but you've clearly got that well in-hand.

At this point, my suspicion is that the sweep job (a Feature called "BLOB Cache Farm Flush") has been deactivated (or was never activated) on the Web Application housing your site collection.  If this Feature isn't active, then the "BLOB Cache Farm Flush Site Collection Administration Support" Feature you're trying to activate from within the site collection won't work (as you're seeing).

Here's how the overall solution works.  The site collection Feature you're trying to activate is responsible for providing the admin page that allows you indicate that you want to perform a BLOB cache flush.  When you initiate a flush, this site admin Feature simply sets a flag that indicates a flush should be performed.  That's where the site admin Feature's responsibilities end.

The sweep job (which is scoped at the Web Application level) is a timer job that regularly checks to see if any of the site collections in its associated Web Application are requesting a flush.  If it picks up a flush request, it then carries out the process of incrementing the flush count and resetting any site collection flags that have been set.  This seem a bit convoluted, but it's done because of SharePoint's own internal security boundaries.

So, how do you get things working?  Go into Central Administration and activate the "BLOB Cache Farm Flush" Feature on the Web Application housing your site collection.  When you do this, the sweep job will be provisioned.  At the same time, the activation will actually take care of enabling the "BLOB Cache Farm Flush Site Collection Administration Support" Feature on all site collections within the Web Application that implement the publishing infrastructure.  You won't have to go back and do this manually unless you explicitly deactivate either the Web Application Feature or its corresponding site collection Feature.

I hope this helps!  If not, post your results and we'll continue to work through any issues you're encountering  :-)

Sep 4, 2009 at 3:42 PM

That was it!  I did read the instructions, but I am guilty of scanning the last few steps and promptly forgetting what I just read!  :)  Thanks for your patience.


Sep 4, 2009 at 3:48 PM


No problem whatsoever; I'm glad to hear that you're up-and-running now.  I would have liked to avoid the use of two Features to keep things simpler (and avoid the very scenario you encountered), but unfortunately it wasn't possible given security boundaries.  :-)

I hope the solution serves you well!