Description
We find it useful to tune merge policy not blindly but looking on segment size and fill ratio.
We're working on a patch that adds a tab to admin page with McCandless-style of segment visualization.
Draft UI is attached (currenly as part of admin.extra).
Please share your ideas if it's ok to put the code in core admin.
More details here
http://search-lucene.com/m/QTPa44cNJ1
https://plus.google.com/+MichaelMcCandless/posts/MJVueTznYnD
http://blog.mikemccandless.com/2011/02/visualizing-lucenes-segment-merges.html