Overview:  A brief discussion of how and when the thumbnail preview images in a Power Pivot Gallery in SharePoint get refreshed.

The Power Pivot Gallery is a specialized document library in SharePoint which utilizes Silverlight to render preview images of the report.  These previews are very helpful for users to quickly see if they have the correct report selected before executing it.

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Ways to Refresh Thumbnail Images

Originally I had thought there would be a timer job which refreshes the thumbnails at a regular interval.  However, that is not the case.  There are 3 ways I’ve found to get thumbnails refreshed:

1.  Upload a new workbook.  The act of uploading a new workbook causes an event handler which will populate the thumbnail image for that workbook.

2.  Modify a workbook. The act of saving an existing workbook causes an event handler which will update the thumbnail image for that workbook.  Even if all you do is Edit Properties and then Save, that’s enough.

3.  Manually execute GallerySnapshot.exe.  This is a Windows service that runs on the app server where Excel Services is installed.  This exe gets called automatically when a file in the Power Pivot Gallery has been added or changed (an itemAdded or itemUpdated event, respectively, as mentioned in #1 and #2 above).  To run it manually, refer to this information:  http://blogs.msdn.com/b/mtn/archive/2010/10/15/how-to-manually-refresh-powerpivot-gallery-thumbnails.aspx.  Note that this service was called GetSnapshot.exe in SharePoint 2010, and has been renamed to GallerySnapshot.exe in SharePoint 2013.  The SharePoint 2013 GallerySnapshot.exe can be found at:  C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\BIN.

The takeaway:  Since the thumbnails only get regenerated in the above circumstances (and not at a regular interval), the preview images shouldn’t be thought of as something that is intended to coincide exactly with data updates.

Finding More Information

Technet – Refresh a Thumbnail Images

MSDN – Refreshing Power Pivot Gallery Thumbnails

Power Pivot Geek – General Problems with Gallery Snapshots Not Being Taken