POC: Improve JDBC driver performance using ByteBufferManager for TDS packet handling

src/main/java/com/microsoft/sqlserver/jdbc/BufferPool.java

@@ -0,0 +1,26 @@
+package com.microsoft.sqlserver.jdbc;
+
+import java.util.Arrays;
+import java.util.concurrent.ConcurrentLinkedQueue;
+
+public class BufferPool {
+    private final int bufferSize;
+    private final ConcurrentLinkedQueue<byte[]> pool = new ConcurrentLinkedQueue<>();
+
+    BufferPool(int bufferSize) {
+        this.bufferSize = bufferSize;
+    }
+
+    public byte[] rent() {
+        byte[] buffer = pool.poll();
+        return buffer == null ? new byte[bufferSize] : buffer;
+    }
+
+    public void release(byte[] buffer) {
+        if (buffer.length == bufferSize) {
+            pool.offer(buffer);
+            Arrays.fill(buffer, (byte) 0); // Clear the array for re-use
+        }
+        // If the buffer size does not match, we do not store it in the pool
+    }
+}

src/main/java/com/microsoft/sqlserver/jdbc/ByteBufferManager.java

@@ -0,0 +1,42 @@
+package com.microsoft.sqlserver.jdbc;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+public class ByteBufferManager {
+
+    private static int[] poolSizes = { 1024, 2048, 4096, 8192, 16384, 32768, 65536 };
+    private final static ConcurrentHashMap<Integer, BufferPool> pools = new ConcurrentHashMap<>();
+
+    public ByteBufferManager() {
+        for (int size : poolSizes) {
+            pools.put(size, new BufferPool(size));
+        }
+    }
+
+    public byte[] rentBytes(int size) {
+        int poolSize = getPoolSize(size);
+
+        if (poolSize == -1) {
+            return new byte[size];
+        }
+        BufferPool pool = pools.computeIfAbsent(poolSize, BufferPool::new);
+        return pool.rent();
+    }
+
+    private static int getPoolSize(int size) {
+        if (size <= 0) return 1024;
+
+        int nextPower = Integer.highestOneBit(size - 1) << 1;
+        return nextPower <= 65536 ? nextPower : -1;
+    }
+
+    // Return a previously rented byte array
+    public void release(byte[] array) {
+        int size = array.length;
+        BufferPool pool = pools.get(size);
+        if (pool != null) {
+            pool.release(array);
+        }
+        // else discard — no pooling for this size
+    }
+}

src/main/java/com/microsoft/sqlserver/jdbc/IOBuffer.java

@@ -6668,18 +6668,25 @@ final class TDSPacket {
     final byte[] payload;
     int payloadLength;
     volatile TDSPacket next;
+    private final ByteBufferManager byteBufferManager;
 
     final public String toString() {
         return "TDSPacket(SPID:" + Util.readUnsignedShortBigEndian(header, TDS.PACKET_HEADER_SPID) + " Seq:"
                 + header[TDS.PACKET_HEADER_SEQUENCE_NUM] + ")";
     }
 
-    TDSPacket(int size) {
-        payload = new byte[size];
+    TDSPacket(int size, ByteBufferManager byteBufferManager) {
+        this.byteBufferManager = byteBufferManager;
+        // payload = new byte[size];
+        payload = byteBufferManager.rentBytes(size);
         payloadLength = 0;
         next = null;
     }
 
+    void releasePayload() {
+        byteBufferManager.release(payload);
+    }
+
     final boolean isEOM() {
         return TDS.STATUS_BIT_EOM == (header[TDS.PACKET_HEADER_MESSAGE_STATUS] & TDS.STATUS_BIT_EOM);
     }
@@ -6738,7 +6745,8 @@ final SQLServerConnection getConnection() {
         return con;
     }
 
-    private transient TDSPacket currentPacket = new TDSPacket(0);
+    private transient ByteBufferManager byteBufferManager = new ByteBufferManager();
+    private transient TDSPacket currentPacket = new TDSPacket(0, byteBufferManager);
     private transient TDSPacket lastPacket = currentPacket;
     private int payloadOffset = 0;
     private int packetNum = 0;
@@ -6854,6 +6862,7 @@ private boolean nextPacket() throws SQLServerException {
             if (logger.isLoggable(Level.FINEST))
                 logger.finest(toString() + " Moving to next packet -- unlinking consumed packet");
 
+            consumedPacket.releasePayload();
             consumedPacket.next = null;
         }
         currentPacket = nextPacket;
@@ -6879,7 +6888,7 @@ final boolean readPacket() throws SQLServerException {
             assert tdsChannel.numMsgsRcvd < tdsChannel.numMsgsSent : "numMsgsRcvd:" + tdsChannel.numMsgsRcvd
                     + " should be less than numMsgsSent:" + tdsChannel.numMsgsSent;
 
-            TDSPacket newPacket = new TDSPacket(con.getTDSPacketSize());
+            TDSPacket newPacket = new TDSPacket(con.getTDSPacketSize(), byteBufferManager);
             if ((null != command) &&
             // if cancelQueryTimeout is set, we should wait for the total amount of
             // queryTimeout + cancelQueryTimeout to