I switched locally from subversion 1.4 to 1.5, our server still runs 1.4. Since then every merge takes ages to perform. What took only a couple of seconds is now in the area of 5-10 minutes (or more). There is no difference between the command line client and tortoise (so we talk about the windows versions).
Has anybody else this strange phenomenon?
We've had problems when trying to add large numbers of files to repositories through the client which I assume created orphaned processes on the server when we killed the crashed client. We had to kill the server processes too and restart the subversion service (we run SVN as a windows service). Our SVN machine is dedicated so we actually just rebooted the box and everything went back to normal.
SVN 1.5 introduced the concept of automatic merge tracking, although I thought it required a 1.5 server and client. See here for details.
Upgrading to 1.5.3 (when it is out) will significantly speed up your merges.
We did some performance analysis on merging last weekend and found two severe performance issues. One of those was very Windows specific and made disk IO while merging much slower than needed and the other was on the type of network connections used. (Too less reuse of existing knowledge)
These fixes and a few others that enhance the merge performance even more will be available in Subversion 1.5.3 that is expected to be released by the end of this week.
[Edit: This performance enhancement is in the code path that assumes your server is 1.5+]