From 8d7b0ac425da17a5491513f30fe8bd65c126db8f Mon Sep 17 00:00:00 2001
From: Gregory Oschwald <goschwald@maxmind.com>
Date: Fri, 12 Jun 2020 09:50:48 -0700
Subject: [PATCH 1/2] Remove use of synchronized around duplicate()

Closes #65, #69, and #72.
---
 CHANGELOG.md                                   |  2 ++
 src/main/java/com/maxmind/db/BufferHolder.java | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6c4e2aa6..3d669965 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,8 @@ CHANGELOG
   control byte in the data section rather than an
   `ArrayIndexOutOfBoundsException`. Reported by Edwin Delgado H. GitHub
   #68.
+* In order to improve performance when lookups are done from multiple
+  threads, a use of `synchronized` has been removed. GitHub #65 & #69.
 
 1.3.1 (2020-03-03)
 ------------------
diff --git a/src/main/java/com/maxmind/db/BufferHolder.java b/src/main/java/com/maxmind/db/BufferHolder.java
index fb781aff..856bebcd 100644
--- a/src/main/java/com/maxmind/db/BufferHolder.java
+++ b/src/main/java/com/maxmind/db/BufferHolder.java
@@ -58,7 +58,22 @@ final class BufferHolder {
      * Returns a duplicate of the underlying ByteBuffer. The returned ByteBuffer
      * should not be shared between threads.
      */
-    synchronized ByteBuffer get() {
+    ByteBuffer get() {
+        // The Java API docs for buffer state:
+        //
+        //     Buffers are not safe for use by multiple concurrent threads. If a buffer is to be used by more than
+        //     one thread then access to the buffer should be controlled by appropriate synchronization.
+        //
+        // As such, you may think that this should be synchronized. This used to be the case, but we had several
+        // complaints about the synchronization causing contention, e.g.:
+        //
+        // * https://github.com/maxmind/MaxMind-DB-Reader-java/issues/65
+        // * https://github.com/maxmind/MaxMind-DB-Reader-java/pull/69
+        //
+        // Given that we are not modifying the original ByteBuffer in any way and all currently known and most
+        // reasonably imaginable implementations of duplicate() only do read operations on the original buffer object,
+        // the risk of not synchronizing this call seems relatively low and worth taking for the performance benefit
+        // when lookups are being done from many threads.
         return this.buffer.duplicate();
     }
 }

From 39d063126df8db2041194856014742ba570cc784 Mon Sep 17 00:00:00 2001
From: Gregory Oschwald <goschwald@maxmind.com>
Date: Fri, 12 Jun 2020 09:53:23 -0700
Subject: [PATCH 2/2] Upgrade Jackson Databind

---
 CHANGELOG.md | 1 +
 pom.xml      | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3d669965..188f7feb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ CHANGELOG
   #68.
 * In order to improve performance when lookups are done from multiple
   threads, a use of `synchronized` has been removed. GitHub #65 & #69.
+* `jackson-databind` has been upgraded to 2.11.0.
 
 1.3.1 (2020-03-03)
 ------------------
diff --git a/pom.xml b/pom.xml
index 2ca25551..d9764a2d 100644
--- a/pom.xml
+++ b/pom.xml
@@ -45,7 +45,7 @@
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>
             <artifactId>jackson-databind</artifactId>
-            <version>2.10.3</version>
+            <version>2.11.0</version>
         </dependency>
     </dependencies>
     <build>