From 28788cc6381bc6c517fa189adb0c42acc6ab2421 Mon Sep 17 00:00:00 2001
From: Dmitry Konstantinov <netudima@gmail.com>
Date: Sat, 23 May 2026 16:55:53 +0100
Subject: [PATCH] Avoid megamorphic call overhead at
 org.apache.cassandra.io.util.RandomAccessReader#current

patch by Dmitry Konstantinov; reviewed by TBD for CASSANDRA-21399
---
 .../v1/vector/RandomAccessReaderAdapter.java   |  4 ++--
 .../cassandra/io/util/RandomAccessReader.java  | 18 ++++++++++++++----
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/java/org/apache/cassandra/index/sai/disk/v1/vector/RandomAccessReaderAdapter.java b/src/java/org/apache/cassandra/index/sai/disk/v1/vector/RandomAccessReaderAdapter.java
index 7448dc0648a3..54371eafc131 100644
--- a/src/java/org/apache/cassandra/index/sai/disk/v1/vector/RandomAccessReaderAdapter.java
+++ b/src/java/org/apache/cassandra/index/sai/disk/v1/vector/RandomAccessReaderAdapter.java
@@ -46,7 +46,7 @@ static ReaderSupplier createSupplier(FileHandle fileHandle)
     @Override
     public void readFully(float[] dest) throws IOException
     {
-        BufferHolder bh = bufferHolder;
+        BufferHolder bh = getBufferHolder();
         long position = getPosition();
 
         FloatBuffer floatBuffer;
@@ -94,7 +94,7 @@ public void read(int[] dest, int offset, int count) throws IOException
         if (count == 0)
             return;
 
-        BufferHolder bh = bufferHolder;
+        BufferHolder bh = getBufferHolder();
         long position = getPosition();
 
         IntBuffer intBuffer;
diff --git a/src/java/org/apache/cassandra/io/util/RandomAccessReader.java b/src/java/org/apache/cassandra/io/util/RandomAccessReader.java
index eb5a18240278..06d35a5b359c 100644
--- a/src/java/org/apache/cassandra/io/util/RandomAccessReader.java
+++ b/src/java/org/apache/cassandra/io/util/RandomAccessReader.java
@@ -38,7 +38,9 @@ public class RandomAccessReader extends RebufferingInputStream implements FileDa
     private long markedPointer;
 
     final Rebufferer rebufferer;
-    protected BufferHolder bufferHolder = Rebufferer.EMPTY;
+    private BufferHolder bufferHolder = Rebufferer.EMPTY;
+
+    private long bufferHolderOffset = 0;
 
     /**
      * Only created through Builder
@@ -67,7 +69,9 @@ private void reBufferAt(long position)
         bufferHolder.release();
         bufferHolder = rebufferer.rebuffer(position);
         buffer = bufferHolder.buffer();
-        buffer.position(Ints.checkedCast(position - bufferHolder.offset()));
+        long newOffset = bufferHolder.offset();
+        bufferHolderOffset = newOffset;
+        buffer.position(Ints.checkedCast(position - newOffset));
 
         assert buffer.order() == ByteOrder.BIG_ENDIAN : "Buffer must have BIG ENDIAN byte ordering";
     }
@@ -80,9 +84,14 @@ public long getFilePointer()
         return current();
     }
 
+    protected BufferHolder getBufferHolder()
+    {
+        return bufferHolder;
+    }
+
     protected long current()
     {
-        return bufferHolder.offset() + buffer.position();
+        return bufferHolderOffset + buffer.position();
     }
 
     public String getPath()
@@ -164,6 +173,7 @@ public void close()
         rebufferer.closeReader();
         buffer = null;
         bufferHolder = null;
+        bufferHolderOffset = 0;
 
         //For performance reasons we don't keep a reference to the file
         //channel so we don't close it
@@ -197,7 +207,7 @@ public void seek(long newPosition)
         if (buffer == null)
             throw new IllegalStateException("Attempted to seek in a closed RAR");
 
-        long bufferOffset = bufferHolder.offset();
+        long bufferOffset = bufferHolderOffset;
         if (newPosition >= bufferOffset && newPosition < bufferOffset + buffer.limit())
         {
             buffer.position((int) (newPosition - bufferOffset));