From 9e04cb9c41bcfb43bb1e8d1bc977ef7ec527aff9 Mon Sep 17 00:00:00 2001
From: Armin Braun <me@obrown.io>
Date: Mon, 8 Jul 2024 10:59:50 +0200
Subject: [PATCH] Override single byte writes to OutputStreamIndexOutput to
 remove locking (#13543)

Single byte writes to BufferedOutputStream show up pretty hot in
indexing benchmarks. We can save the locking overhead introduced by
JEP374 by overriding and providing a no-lock fastpath.
---
 .../lucene/store/OutputStreamIndexOutput.java      | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lucene/core/src/java/org/apache/lucene/store/OutputStreamIndexOutput.java b/lucene/core/src/java/org/apache/lucene/store/OutputStreamIndexOutput.java
index 5c3b4dbd88a..14b56a67e8a 100644
--- a/lucene/core/src/java/org/apache/lucene/store/OutputStreamIndexOutput.java
+++ b/lucene/core/src/java/org/apache/lucene/store/OutputStreamIndexOutput.java
@@ -135,5 +135,19 @@ public class OutputStreamIndexOutput extends IndexOutput {
       BitUtil.VH_LE_LONG.set(buf, count, i);
       count += Long.BYTES;
     }
+
+    @Override
+    public void write(int b) throws IOException {
+      // override single byte write to avoid synchronization overhead now that JEP374 removed biased
+      // locking
+      byte[] buffer = buf;
+      int count = this.count;
+      if (count >= buffer.length) {
+        super.write(b);
+      } else {
+        buffer[count] = (byte) b;
+        this.count = count + 1;
+      }
+    }
   }
 }