svn commit: r1381785 - /subversion/trunk/subversion/libsvn_subr/cache-membuffer.c

[stefan2]

Author: stefan2
Date: Thu Sep  6 22:21:34 2012
New Revision: 1381785

URL: http://svn.apache.org/viewvc?rev=1381785&view=rev
Log:
Optimize replacing / updating handling in membuffer caches:
reduce the data churn by reusing the existing entry if possible.

* subversion/libsvn_subr/cache-membuffer.c
  (membuffer_cache_set_internal): try to recycle the old entry

Modified:
    subversion/trunk/subversion/libsvn_subr/cache-membuffer.c

Modified: subversion/trunk/subversion/libsvn_subr/cache-membuffer.c
URL: 
http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/cache-membuffer.c?rev=1381785&r1=1381784&r2=1381785&view=diff
==============================================================================
--- subversion/trunk/subversion/libsvn_subr/cache-membuffer.c (original)
+++ subversion/trunk/subversion/libsvn_subr/cache-membuffer.c Thu Sep  6 
22:21:34 2012
@@ -1168,13 +1168,8 @@ membuffer_cache_set_internal(svn_membuff
       && cache->max_entry_size >= size
       && ensure_data_insertable(cache, size))
     {
-      /* Remove old data for this key, if that exists.
-       * Get an unused entry for the key and and initialize it with
-       * the serialized item's (future) posion within data buffer.
-       */
-      entry_t *entry = find_entry(cache, group_index, to_find, TRUE);
-      entry->size = size;
-      entry->offset = cache->current_data;
+      /* first, look for a previous entry for the given key */
+      entry_t *entry = find_entry(cache, group_index, to_find, FALSE);
 
 #ifdef SVN_DEBUG_CACHE_MEMBUFFER
 
@@ -1185,14 +1180,32 @@ membuffer_cache_set_internal(svn_membuff
 
 #endif
 
+      /* if there is an old version of that entry and the new data fits into
+       * the old spot, just re-use that space. */
+      if (entry && entry->size >= size)
+        {
+          entry->size = size;
+        }
+      else
+        {
+          /* Remove old data for this key, if that exists.
+           * Get an unused entry for the key and and initialize it with
+           * the serialized item's (future) posion within data buffer.
+           */
+          entry = find_entry(cache, group_index, to_find, TRUE);
+          entry->size = size;
+          entry->offset = cache->current_data;
+
+          /* Link the entry properly.
+           */
+          insert_entry(cache, entry);
+        }
+
       /* Copy the serialized item data into the cache.
        */
       if (size)
         memcpy(cache->data + entry->offset, buffer, size);
 
-      /* Link the entry properly.
-       */
-      insert_entry(cache, entry);
       cache->total_writes++;
     }
   else