Database corruption with error svn: locate_key: no such string: 'f9a'

NOTE: This seems to be very hard to reproduce, but there have been at least two occurrences 
recently and I want to put something in the Issue Tracker for others to find. 

My case: Subversion 0.24.2, Mac OS X 10.2.6, Apache web server 2.0.46 all built from the release 
tarball, all non-admin access via http. Back end is Berkeley DB 4.1.25 built from release tarball. 

OK, the repository is seriously toast. After restoring from a backup, we tried to check in additional 
changes and ran into tons of problems. Individual files keep causing repository deaths with errors 
like:

subversion/libsvn_fs/bdb/strings-table.c:101: (apr_err=160010)
svn: Filesystem has no such string
svn: locate_key: no such string `h6w'

Worse, it's inconsistent throughout the repository. Most files work. Some files don't, consistently. 
Occasionally, if we delete a file from the head of the tree, add back a small file (like only a few 
bytes), then replace it in the wc with the real (~1.5-2 MB file) and do a check-in it works. Other 
times it doesn't. The error code is consistent, but the 3 letters `h6w' are not -- other times they 
are `f8r' or other letter-number-letter combos. The repository dies the same way when I run 
'svnadmin dump' on it, even after running 'svnadmin restore'.

Also, prior to going to the backup copy of the repository, we ran 'svnadmin recover' on the 
repository as we were getting the error:

Berkeley DB error while opening `copies' table for filesystem /Library/Repository/
MacOSXTroubleshooting/db: Invalid argument

whenever we tried any operation on the repository. 

Follow the threads on the users@subversion.tigris.org list with the titles: "Berkeley DB corruption - 
'changes' table (again)" and "Dump: Filesystem has no such string " for more detail. 

http://subversion.tigris.org/servlets/ReadMsg?list=users&msgNo=1928
http://subversion.tigris.org/servlets/ReadMsg?list=users&msgNo=1653

Original issue reported by psuh