High fds (#205)

* Having a Large Number as File Descriptor Limit

* xx

* headline too short

* Update apx-issues.rst

---------

Co-authored-by: Valentin Volkl <valentin.volkl@cern.ch>

Author: HereThereBeDragons

apx-issues.rst

@@ -1,6 +1,15 @@
 Known Issues
 ============
 
+Slow Performance with a Very Large File Descriptor Limit
+---------------------------------------------------
+
+Before CernVM-FS 2.11, having the file descriptor limit set to a very large number
+will result in a very slow ``cvmfs`` performance in certain situations.
+This is due to certain operations looping over all possible file descriptors,
+instead of just the used/opened ones.
+This issue is resolved in CernVM-FS 2.11.
+
 Publisher nodes with AUFS and XFS
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