Merge pull request #18706 from ghalliday/issue31953

HPCC-31953 Avoid memory allocation when reading an index node Reviewed-By: Richard Chapman <[email protected]> Merged-by: Gavin Halliday <[email protected]>
hpcc-systems · May 31, 2024 · 758edb9 · 758edb9
2 parents c8c0b4e + 485be94
commit 758edb9
Showing 1 changed file with 10 additions and 1 deletion.
diff --git a/system/jhtree/jhtree.cpp b/system/jhtree/jhtree.cpp
@@ -1244,8 +1244,17 @@ const CJHTreeNode *CDiskKeyIndex::loadNode(cycle_t * fetchCycles, offset_t pos,
     nodesLoaded++;
     if (!useIO) useIO = io;
     unsigned nodeSize = keyHdr->getNodeSize();
+
+    //Use alloca() to allocate a buffer on the stack if the node size is small enough.
+    //Often the data could be read directly from the input files's buffer and not even be copied.
+    //Should we have a io->peek(pos, size) which returns a pointer if supported?
+    constexpr const size_t maxStackSize = 8192; // Default node size
     MemoryAttr ma;
-    char *nodeData = (char *) ma.allocate(nodeSize);
+    char *nodeData;
+    if (nodeSize <= maxStackSize)
+        nodeData = (char *) alloca(nodeSize);
+    else
+        nodeData = (char *) ma.allocate(nodeSize);
     assertex(nodeData);
 
     CCycleTimer fetchTimer(fetchCycles != nullptr);