DOCS-11245, DOCS-11470: read concern snapshot part 1

source/reference/read-concern-local.txt

@@ -9,8 +9,8 @@ Read Concern ``"local"``
 ========================
 
 .. meta::
-   :description: read concern, local read concern, read isolation
-   :keywords: read concern, local read concern, read isolation
+   :description: read concern, local read concern, read isolation, transactions, multi-document transactions
+   :keywords: read concern, local read concern, read isolation, transactions, multi-document transactions
 
 
 A query with read concern ``"local"`` returns the instance's most
@@ -33,6 +33,40 @@ Causally Consistent Sessions
 Read concern :readconcern:`local` is available for use with causally
 consistent sessions.
 
+Read Concern ``"local"`` and Transactions
+--------------------------------------------
+
+In a multi-document transaction, read concern levels
+:readconcern:`"local"` and :readconcern:`"snapshot"` are available for
+:ref:`read and write operations that support read concern in a
+transaction <read-concern-operations>`.
+
+.. note::
+
+   For the operations in a transaction, you set the read concern at the
+   transaction level, not at the individual operation level.
+
+.. seealso:: :readconcern:`"snapshot"`
+
+Write Operations and Read Concern ``"local"``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In a multi-document transaction, both the read operations and the write
+operations can accept the read concern level :readconcern:`"local"`.
+The following write operations can accept a read concern level as part
+of a transaction:
+
+- :dbcommand:`delete`
+
+- :dbcommand:`findAndModify`
+
+- :dbcommand:`insert`
+
+- :dbcommand:`update`
+
+For a list of all operations that accept read concerns, see
+:ref:`read-concern-operations`.
+
 Example
 -------
 

source/reference/read-concern-snapshot.txt

@@ -0,0 +1,75 @@
+.. default-domain:: mongodb
+
+.. class:: hidden
+
+   .. readconcern:: "snapshot"
+
+===========================
+Read Concern ``"snapshot"``
+===========================
+
+.. meta::
+   :description: read concern, snapshot read concern, read isolation, transactions, multi-document transactions
+   :keywords: read concern, snapshot read concern, read isolation, transactions, multi-document transactions
+
+.. versionadded:: 4.0
+
+Read concern ``"snapshot"`` is only available for multi-document
+transactions.
+
+- If the transaction is not part of a :ref:`causally consistent session
+  <sessions>`, operations with read concern ``"snapshot"`` reads data
+  from a snapshot of the most recent majority committed data at
+  transaction start.
+
+- If the transaction is part of a :ref:`causally consistent session
+  <sessions>`, operations with read concern ``"snapshot"`` reads data
+  from a snapshot of the first majority committed data that guarantees
+  causal consistency with the operation immediately prior to the
+  transaction start. The time of the snapshot may be after the
+  transaction start to guarantee causal consistency.
+
+Read Concern ``"snapshot"`` and Transactions
+--------------------------------------------
+
+In a multi-document transaction, read concern levels
+:readconcern:`"local"` and :readconcern:`"snapshot"` are available for
+:ref:`read and write operations that support read concern in a
+transaction <read-concern-operations>`.
+
+.. note::
+
+   For the operations in a transaction, you set the read concern at the
+   transaction level, not at the individual operation level.
+
+.. seealso:: :readconcern:`"local"`
+
+Write Operations and Read Concern ``"snapshot"``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In a multi-document transaction, both the read operations and the write
+operations can accept the read concern level :readconcern:`"snapshot"`.
+The following write operations can accept a read concern level as part
+of a transaction:
+
+- :dbcommand:`delete`
+
+- :dbcommand:`findAndModify`
+
+- :dbcommand:`insert`
+
+- :dbcommand:`update`
+
+For a list of all operations that accept read concerns, see
+:ref:`read-concern-operations`.
+
+Causally Consistent Sessions
+----------------------------
+
+:readconcern:`snapshot` is available for transactions that are part of
+a causally consistent session.
+
+If the transaction is part of a :ref:`causally consistent session
+<sessions>`, the snapshot of the majority committed data reflects the
+earliest time from the transaction start time(inclusive) that
+guarantees causally consistency with the prior operation in the session.