From 3a6b9402d5f45b27b46861b21088e4eaedbacd2f Mon Sep 17 00:00:00 2001
From: Grisha Kotler <grisha@ravendb.net>
Date: Wed, 5 Mar 2025 14:32:59 +0200
Subject: [PATCH] RavenDB-23704 - Move allocation pointer back when releasing
 memory at current allocation boundary

---
 src/Sparrow.Server/ByteString.cs          |  6 +++-
 test/FastTests/Sparrow/ByteStringTests.cs | 34 ++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/Sparrow.Server/ByteString.cs b/src/Sparrow.Server/ByteString.cs
index 0212954a7ac2..f7f274fb05fe 100644
--- a/src/Sparrow.Server/ByteString.cs
+++ b/src/Sparrow.Server/ByteString.cs
@@ -1336,7 +1336,11 @@ public void Release(ref ByteString value)
 
             int reusablePoolIndex = GetPoolIndexForReuse(value._pointer->Size);
 
-            if (value._pointer->Size <= ByteStringContext.MinBlockSizeInBytes)
+            if (value._pointer == _internalCurrent.Current - value._pointer->Size)
+            {
+                _internalCurrent.Current -= value._pointer->Size;
+            }
+            else if (value._pointer->Size <= ByteStringContext.MinBlockSizeInBytes)
             {
                 FastStack<IntPtr> pool = _internalReusableStringPool[reusablePoolIndex];
                 if (pool == null)
diff --git a/test/FastTests/Sparrow/ByteStringTests.cs b/test/FastTests/Sparrow/ByteStringTests.cs
index 2bde72effc69..0b3210d337de 100644
--- a/test/FastTests/Sparrow/ByteStringTests.cs
+++ b/test/FastTests/Sparrow/ByteStringTests.cs
@@ -1,4 +1,4 @@
-using System;
+using Sparrow.Global;
 using Sparrow.Server;
 using Sparrow.Threading;
 using Tests.Infrastructure;
@@ -195,6 +195,38 @@ public void CanResetAllocationBlockSize()
             }
         }
 
+        [RavenFact(RavenTestCategory.Memory)]
+        public void CanReuseMemory()
+        {
+            using (var context = new ByteStringContext<ByteStringDirectAllocator>(SharedMultipleUseFlag.None))
+            {
+                while (context.AllocationBlockSize != 2 * Constants.Size.Megabyte)
+                {
+                    context.Allocate(ByteStringContext.MinBlockSizeInBytes / 2, out _);
+                }
+
+                Assert.Equal(2 * Constants.Size.Megabyte, context.AllocationBlockSize);
+
+                const int toAllocate = ByteStringContext.MinBlockSizeInBytes * 5;
+                context.Allocate(toAllocate, out var first);
+                var ptrLocation = (long)first._pointer;
+                var allocatedBefore = context._totalAllocated;
+                context.Release(ref first);
+
+                for (var i = 0; i < 512; i++)
+                {
+                    var allocation = i % 2 == 0 ? toAllocate / 2 : toAllocate;
+                    context.Allocate(allocation, out var byteString);
+
+                    Assert.Equal(ptrLocation, (long)byteString._pointer);
+
+                    context.Release(ref byteString);
+                }
+
+                Assert.Equal(allocatedBefore, context._totalAllocated);
+            }
+        }
+
 #if VALIDATE
         [Fact]
         public void ValidationKeyAfterAllocateAndReleaseReuseShouldBeDifferent()