cache MIB columnar objects instance ID <-> symbolic representation mapping

for performance reasons

2 files changed, 48 insertions, 2 deletions

diff --git a/pysnmp/cache.py b/pysnmp/cache.py
new file mode 100644
index 0000000..4023c46
--- /dev/null
+++ b/pysnmp/cache.py
@@ -0,0 +1,37 @@
+# Limited-size dictionary class to use for caches
+
+class Cache:
+    def __init__(self, maxSize=256):
+        self.__maxSize = maxSize
+        self.__size = 0
+        self.__chopSize = maxSize/10
+        self.__chopSize = self.__chopSize and self.__chopSize or 1
+        self.__cache = {}
+        self.__usage = {}
+
+    def __contains__(self, k): return k in self.__cache
+
+    def __getitem__(self, k):
+        self.__usage[k] = self.__usage[k] + 1
+        return self.__cache[k]
+
+    def __len__(self): return self.__size
+        
+    def __setitem__(self, k, v):
+        if self.__size >= self.__maxSize:
+            keys = self.__usage.keys()
+            keys.sort(lambda x,y,d=self.__usage: cmp(d[x],d[y]))
+            print keys[:self.__chopSize]
+            for _k in keys[:self.__chopSize]:
+                del self.__cache[_k]
+                del self.__usage[_k]
+            self.__size = self.__size - self.__chopSize
+        if k not in self.__cache:
+            self.__size = self.__size + 1
+            self.__usage[k] = 0L
+        self.__cache[k] = v
+
+    def __delitem__(self, k):
+        del self.__cache[k]
+        del self.__usage[k]
+        self.__size = self.__size - 1
diff --git a/pysnmp/smi/mibs/SNMPv2-SMI.py b/pysnmp/smi/mibs/SNMPv2-SMI.py
index a47ca93..9af9477 100644
--- a/pysnmp/smi/mibs/SNMPv2-SMI.py
+++ b/pysnmp/smi/mibs/SNMPv2-SMI.py
@@ -4,7 +4,7 @@ from pysnmp.smi import exval, error
 from pysnmp.proto import rfc1902
 from pyasn1.type import constraint
 from pyasn1.error import ValueConstraintError, PyAsn1Error
-from pysnmp import debug
+from pysnmp import cache, debug
 
 ( Integer, ObjectIdentifier, Null ) = mibBuilder.importSymbols("ASN1", "Integer", "ObjectIdentifier", "Null")
 
@@ -756,6 +756,8 @@ class MibTableRow(MibTree):
     """
     def __init__(self, name):
         MibTree.__init__(self, name)
+        self.__idToIdxCache = cache.Cache()
+        self.__idxToIdCache = cache.Cache()
         self.indexNames = ()
         self.augmentingRows = {}
 
@@ -962,6 +964,8 @@ class MibTableRow(MibTree):
 
     def getIndicesFromInstId(self, instId):
         """Return index values for instance identification"""
+        if instId in self.__idToIdxCache:
+            return self.__idToIdxCache[instId]
         indices = []
         for impliedFlag, modName, symName in self.indexNames:
             mibObj, = mibBuilder.importSymbols(modName, symName)
@@ -972,10 +976,14 @@ class MibTableRow(MibTree):
                 'Excessive instance identifier sub-OIDs left at %s: %s' %
                 (self, instId)
                 )
-        return tuple(indices)
+        indices = tuple(indices)
+        self.__idToIdxCache[instId] = indices
+        return indices
 
     def getInstIdFromIndices(self, *indices):
         """Return column instance identification from indices"""
+        if indices in self.__idxToIdCache:
+          return self.__idxToIdCache[indices]
         idx = 0; idxLen = len(indices); instId = ()
         for impliedFlag, modName, symName in self.indexNames:
             mibObj, = mibBuilder.importSymbols(modName, symName)
@@ -986,6 +994,7 @@ class MibTableRow(MibTree):
             else:
                 break
             idx = idx + 1
+        self.__idxToIdCache[indices] = instId
         return instId
 
     # Table access by index