Optimizations for ClientCache, especially under PyPy.

- make the locked decorator easier to inline by not creating a new closure every time.
- use builtin dicts instead of the pure-python BTrees (only under pypy)

"Transaction",                  AFTER    BEFORE
"Add 3000 Objects",             10014      8777
"Update 3000 Objects",          12199      8805
"Read 3000 Warm Objects",        4294      3699
"Read 3000 Cold Objects",        4264      3676
"Read 3000 Hot Objects",        79764     58732
"Read 3000 Steamin' Objects", 2667283   2574508

src/ZEO/cache.py

@@ -36,6 +36,7 @@ import ZODB.fsIndex
 import zc.lockfile
 from ZODB.utils import p64, u64, z64
 import six
+from ._compat import PYPY
 
 logger = logging.getLogger("ZEO.cache")
 
@@ -130,21 +131,23 @@ allocated_record_overhead = 43
 # to the end of the file that the new object can't fit in one
 # contiguous chunk, currentofs is reset to ZEC_HEADER_SIZE first.
 
-class locked(object):
 
-    def __init__(self, func):
-        self.func = func
-
-    def __get__(self, inst, class_):
-        if inst is None:
-            return self
-        def call(*args, **kw):
+def locked(func):
+    def _locked_wrapper(inst, *args, **kwargs):
         inst._lock.acquire()
         try:
-                return self.func(inst, *args, **kw)
+            return func(inst, *args, **kwargs)
         finally:
             inst._lock.release()
-        return call
+    return _locked_wrapper
+
+# Under PyPy, the available dict specializations perform significantly
+# better (faster) than the pure-Python BTree implementation. They may
+# use less memory too. And we don't require any of the special BTree features...
+_current_index_type = ZODB.fsIndex.fsIndex if not PYPY else dict
+_noncurrent_index_type = BTrees.LOBTree.LOBTree if not PYPY else dict
+# ...except at this leaf level
+_noncurrent_bucket_type = BTrees.LLBTree.LLBucket
 
 class ClientCache(object):
     """A simple in-memory cache."""
@@ -173,13 +176,13 @@ class ClientCache(object):
         self._len = 0
 
         # {oid -> pos}
-        self.current = ZODB.fsIndex.fsIndex()
+        self.current = _current_index_type()
 
         # {oid -> {tid->pos}}
         # Note that caches in the wild seem to have very little non-current
         # data, so this would seem to have little impact on memory consumption.
         # I wonder if we even need to store non-current data in the cache.
-        self.noncurrent = BTrees.LOBTree.LOBTree()
+        self.noncurrent = _noncurrent_index_type()
 
         # tid for the most recent transaction we know about.  This is also
         # stored near the start of the file.
@@ -276,8 +279,8 @@ class ClientCache(object):
         # Remember the location of the largest free block.  That seems a
         # decent place to start currentofs.
 
-        self.current = ZODB.fsIndex.fsIndex()
-        self.noncurrent = BTrees.LOBTree.LOBTree()
+        self.current = _current_index_type()
+        self.noncurrent = _noncurrent_index_type()
         l = 0
         last = ofs = ZEC_HEADER_SIZE
         first_free_offset = 0
@@ -369,7 +372,7 @@ class ClientCache(object):
     def _set_noncurrent(self, oid, tid, ofs):
         noncurrent_for_oid = self.noncurrent.get(u64(oid))
         if noncurrent_for_oid is None:
-            noncurrent_for_oid = BTrees.LLBTree.LLBucket()
+            noncurrent_for_oid = _noncurrent_bucket_type()
             self.noncurrent[u64(oid)] = noncurrent_for_oid
         noncurrent_for_oid[u64(tid)] = ofs