On the 1.10-cache-improvements branch: In the membuffer cache, eliminate storage and most processing overhead for fixed-length keys that don't exceed the size of fingerprint.
On the 1.10-cache-improvements branch:
In the membuffer cache, eliminate storage and most processing overhead for
fixed-length keys that don't exceed the size of fingerprint.

We use the prefix indexes returned by the prefix_pool to uniquely identify
the prefix.  Then the combination of prefix index and key stored in the
fingerprint is unique, too, and can never conflict.  No full key construction,
storage and comparison is needed in that case.

* subversion/libsvn_subr/cache-membuffer.c
  (): Update global description.
  (entry_key_t): Add the PREFIX_IDX element and explain its relationship
                 with the KEY_LEN of the full key.
  (full_key_t): Update docstring to explain the optimized case.
  (entry_keys_match): One element more to compare.
  (find_entry): Update commentary on what KEY_LEN=0 implies.
  (combine_key): Only construct the full key if we can't use the optimization.
  (svn_cache__create_membuffer_cache): For short fixed-len keys, try to
                                       enable the optimized key handling.

git-svn-id: 9abecf2226429f900b686d5b950d6ce0235536c5@1677525 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion