CASSANDRA-21216/CASSANDRA-21260: Clear savedBuffer and savedNextKey in BTree.FastBuilder.reset()

CHANGES.txt

@@ -1,4 +1,5 @@
 5.0.9
+ * BTree.FastBuilder.reset() fails to clear savedBuffer and savedNextKey, causing ClassCastException and SSTable header corruption during schema disagreement (CASSANDRA-21216, CASSANDRA-21260)
  * Fix failing select on system_views.settings for non-string keys (CASSANDRA-21348)
  * Ensure SAI sends range tombstones to the coordinator for queries on static columns (CASSANDRA-21332)
 Merged from 4.1:

src/java/org/apache/cassandra/utils/btree/BTree.java

@@ -3269,11 +3269,58 @@ final LeafBuilder leaf()
 
         /**
          * Clear any references we might still retain, to avoid holding onto memory.
-         * <p>
-         * While this method is not strictly  necessary, it exists to
-         * ensure the implementing classes are aware they must handle it.
          */
-        abstract void reset();
+        void reset()
+        {
+            leaf().count = 0;
+            clearLeafBuffer(leaf().buffer);
+            if (leaf().savedBuffer != null && leaf().savedBuffer[0] != null)
+                Arrays.fill(leaf().savedBuffer, null);
+            leaf().savedNextKey = null;
+            BranchBuilder branch = leaf().parent;
+            while (branch != null && branch.inUse)
+            {
+                branch.count = 0;
+                clearBranchBuffer(branch.buffer);
+                if (branch.savedBuffer != null && branch.savedBuffer[0] != null)
+                    Arrays.fill(branch.savedBuffer, null); // by definition full, if non-empty
+                branch.savedNextKey = null;
+                branch.inUse = false;
+                branch = branch.parent;
+            }
+        }
+
+        /**
+         * Clear the contents of a leaf buffer, aborting once we encounter a null entry
+         * to save time on small trees
+         */
+        private void clearLeafBuffer(Object[] array)
+        {
+            if (array[0] == null)
+                return;
+            // find first null entry; loop from beginning, to amortise cost over size of working set
+            int i = 1;
+            while (i < array.length && array[i] != null)
+                ++i;
+            Arrays.fill(array, 0, i, null);
+        }
+
+        /**
+         * Clear the contents of a branch buffer, aborting once we encounter a null entry
+         * to save time on small trees
+         */
+        private void clearBranchBuffer(Object[] array)
+        {
+            if (array[0] == null)
+                return;
+
+            // find first null entry; loop from beginning, to amortise cost over size of working set
+            int i = 1;
+            while (i < MAX_KEYS && array[i] != null)
+                ++i;
+            Arrays.fill(array, 0, i, null);
+            Arrays.fill(array, MAX_KEYS, MAX_KEYS + i + 1, null);
+        }
     }
 
     /**
@@ -3325,21 +3372,6 @@ public void close()
             }
         }
 
-        @Override
-        void reset()
-        {
-            Arrays.fill(leaf().buffer, null);
-            leaf().count = 0;
-            BranchBuilder branch = leaf().parent;
-            while (branch != null && branch.inUse)
-            {
-                Arrays.fill(branch.buffer, null);
-                branch.count = 0;
-                branch.inUse = false;
-                branch = branch.parent;
-            }
-        }
-
         public boolean validateEmpty()
         {
             LeafOrBranchBuilder cur = leaf();
@@ -3368,56 +3400,6 @@ private static boolean hasOnlyNulls(Object[] buffer)
 
     private static abstract class AbstractUpdater extends AbstractFastBuilder implements AutoCloseable
     {
-        void reset()
-        {
-            assert leaf().count == 0;
-            clearLeafBuffer(leaf().buffer);
-            if (leaf().savedBuffer != null)
-                Arrays.fill(leaf().savedBuffer, null);
-
-            BranchBuilder branch = leaf().parent;
-            while (branch != null && branch.inUse)
-            {
-                assert branch.count == 0;
-                clearBranchBuffer(branch.buffer);
-                if (branch.savedBuffer != null && branch.savedBuffer[0] != null)
-                    Arrays.fill(branch.savedBuffer, null); // by definition full, if non-empty
-                branch.inUse = false;
-                branch = branch.parent;
-            }
-        }
-
-        /**
-         * Clear the contents of a branch buffer, aborting once we encounter a null entry
-         * to save time on small trees
-         */
-        private void clearLeafBuffer(Object[] array)
-        {
-            if (array[0] == null)
-                return;
-            // find first null entry; loop from beginning, to amortise cost over size of working set
-            int i = 1;
-            while (i < array.length && array[i] != null)
-                ++i;
-            Arrays.fill(array, 0, i, null);
-        }
-
-        /**
-         * Clear the contents of a branch buffer, aborting once we encounter a null entry
-         * to save time on small trees
-         */
-        private void clearBranchBuffer(Object[] array)
-        {
-            if (array[0] == null)
-                return;
-
-            // find first null entry; loop from beginning, to amortise cost over size of working set
-            int i = 1;
-            while (i < MAX_KEYS && array[i] != null)
-                ++i;
-            Arrays.fill(array, 0, i, null);
-            Arrays.fill(array, MAX_KEYS, MAX_KEYS + i + 1, null);
-        }
     }
 
     /**