From dde166665b39a008c0fd66bdd36e25649cdbee31 Mon Sep 17 00:00:00 2001
From: Kseniia Antonova <xuniq.is.here@gmail.com>
Date: Fri, 29 May 2026 11:28:29 +0300
Subject: [PATCH] Add a note about `memtx.memory` estimation

Fixes https://github.com/tarantool/doc/issues/5525
---
 doc/platform/storage/memtx.rst                          | 9 +++++++++
 doc/reference/configuration/configuration_reference.rst | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/doc/platform/storage/memtx.rst b/doc/platform/storage/memtx.rst
index 520076d24d..d89e34dca5 100644
--- a/doc/platform/storage/memtx.rst
+++ b/doc/platform/storage/memtx.rst
@@ -14,11 +14,20 @@ This topic describes how to define basic settings related to in-memory storage i
 For the specific settings related to allocator or sorting threads,
 check the corresponding ``memtx`` options in the :ref:`Configuration reference <configuration_reference_memtx>`.
 
+..  note_memtx_memory_estimation_start
+
 ..  NOTE::
 
+    By default, the memory size (``memtx.memory``) parameter is set to 256 MB.
+    Before deploying a cluster, calculate the necessary amount of memory with a reserve and specify it in the
+    ``memtx.memory`` option.
+    Starting a cluster with the default memory size value may lead to memory exhaustion and make further writes
+    to the replica instance impossible.
     To estimate the required amount of memory, you can use the
     `sizing calculator <https://www.tarantool.io/en/sizing_calculator/>`_.
 
+..  note_memtx_memory_estimation_end
+
 ..  _configuration_memtx-memory:
 
 Memory size
diff --git a/doc/reference/configuration/configuration_reference.rst b/doc/reference/configuration/configuration_reference.rst
index 462ab5da6d..9abad54a48 100644
--- a/doc/reference/configuration/configuration_reference.rst
+++ b/doc/reference/configuration/configuration_reference.rst
@@ -3323,6 +3323,10 @@ The ``memtx`` section is used to configure parameters related to the :ref:`memtx
     The server does not go beyond the ``memtx.memory`` limit to allocate tuples, but there is additional memory
     used to store indexes and connection information.
 
+    ..  include:: /platform/storage/memtx.rst
+        :start-after: note_memtx_memory_estimation_start
+        :end-before: note_memtx_memory_estimation_end
+
     **Example**
 
     In the example below, the memory size is set to 1 GB (1073741824 bytes).