(DOCSP-31297): Backport DOCSP-11123 to v6.0. (#3622) (#3849)

* (DOCSP-11123): Updated the wording around durability.

* (DOCSP-11123): Incorporated Melissa's feedback.

* (DOCSP-11123): Incorporated Melissa's feedback.

* (DOCSP-11123): Incorporated Melissa's feedback.

Author: corryroot

source/core/causal-consistency-read-write-concerns.txt

@@ -6,9 +6,10 @@ Causal Consistency and Read and Write Concerns
 
 With MongoDB's :ref:`causally consistent client sessions <sessions>`,
 different combinations of read and write concerns provide different
-:ref:`causal consistency guarantees <causal-consistency-guarantees>`. When
-causal consistency is defined to imply durability, then the following table lists
-the specific guarantees provided by the various combinations:
+:ref:`causal consistency guarantees <causal-consistency-guarantees>`. 
+
+The following table lists the specific guarantees that various 
+combinations provide:
 
 .. list-table::
    :header-rows: 1
@@ -48,24 +49,27 @@ the specific guarantees provided by the various combinations:
      - |checkmark|
      - 
 
-If causal consistency implies durability, then, as seen from the table,
-only read operations with :readconcern:`"majority"` read concern and
-write operations with :writeconcern:`"majority"` write concern can
-guarantee all four causal consistency guarantees. That is,
+If you want causal consistency with data durability, then, as 
+seen from the table, only read operations with 
+:readconcern:`"majority"` read concern and write operations with 
+:writeconcern:`"majority"` write concern can guarantee all four causal 
+consistency guarantees. That is, 
 :ref:`causally consistent client sessions <sessions>` can only
 guarantee causal consistency for:
 
-- Read operations with :readconcern:`"majority"` read concern; i.e. the
-  read operations that return data that has been acknowledged by a
-  majority of the replica set members and is durable.
+- Read operations with :readconcern:`"majority"` read concern; in other 
+  words, the read operations that return data that has been 
+  acknowledged by a majority of the replica set members and is durable.
 
-- Write operations with :writeconcern:`"majority"` write concern; i.e.
-  the write operations that request acknowledgement that the operation
-  has been applied to a majority of the replica set's voting members.
+- Write operations with :writeconcern:`"majority"` write concern; 
+  in other words, the write operations that request acknowledgement 
+  that the operation has been applied to a majority of the replica 
+  set's voting members.
 
-If causal consistency does not imply durability (i.e. writes may be
-rolled back), then write operations with :writeconcern:`{ w: 1 }
-<\<number\>>` write concern can also provide causal consistency. 
+If you want causal consistency without data durability (meaning that 
+writes may be rolled back), then write operations with 
+:writeconcern:`{ w: 1 } <\<number\>>` write concern can also provide 
+causal consistency. 
 
 .. note::
 
@@ -190,8 +194,8 @@ the following causal consistency guarantees:
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state of the data after Read\ :sub:`1` (i.e. an
-          earlier state reflects the data read by Read\ :sub:`1`).
+          reflects a state of the data after Read\ :sub:`1` (meaning 
+          that an earlier state reflects the data read by Read\ :sub:`1`).
 
 .. note:: Scenario 2 (Read Concern "majority" and Write Concern "majority")
 
@@ -244,7 +248,7 @@ the following causal consistency guarantees:
       * - |checkmark| **Monotonic reads**
 
         - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that reflects
-          a state after Read\ :sub:`1` (i.e. an earlier state is
+          a state after Read\ :sub:`1` (meaning that an earlier state is
           reflected in the data read by Read\ :sub:`1`).
 
       * - |checkmark| **Monotonic writes**
@@ -255,8 +259,8 @@ the following causal consistency guarantees:
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state of the data after Read\ :sub:`1` (i.e. an
-          earlier state reflects the data read by Read\ :sub:`1`).
+          reflects a state of the data after Read\ :sub:`1` (meaning 
+          that an earlier state reflects the data read by Read\ :sub:`1`).
 
 .. _causal-rc-majority-wc-1:
 
@@ -265,11 +269,12 @@ Read Concern ``"majority"`` and Write concern ``{w: 1}``
 
 The use of read concern :readconcern:`"majority"` and write concern
 :writeconcern:`{ w: 1 } <\<number\>>` in a causally consistent session
-provides the following causal consistency guarantees *if causal consistency implies durability*:
+provides the following causal consistency guarantees *if you want 
+causal consistency with data durability*:
 
 |xmark| Read own writes  |checkmark| Monotonic reads  |xmark| Monotonic writes  |checkmark| Writes follow reads
 
-*If causal consistency does not imply durability*:
+*If you want causal consistency without data durability*:
 
 |checkmark| Read own writes  |checkmark| Monotonic reads  |checkmark| Monotonic writes  |checkmark| Writes follow reads
 
@@ -279,8 +284,8 @@ provides the following causal consistency guarantees *if causal consistency impl
    :sub:`old` and ``P``\ :sub:`new` can fulfill writes with
    :writeconcern:`{ w: 1 } <\<number\>>` write concern, a client session
    could issue the following sequence of operations
-   successfully but not be causally consistent **if causal consistency
-   implies durability**:
+   successfully but not be causally consistent **if you want causal 
+   consistency with data durability**:
 
    .. list-table::
       :header-rows: 1
@@ -315,21 +320,21 @@ provides the following causal consistency guarantees *if causal consistency impl
 
    - Write\ :sub:`1` will roll back when the network partition is healed.
 
-   |arrow| *If causal consistency implies durability*
+   |arrow| *If you want causal consistency with data durability*
 
    .. list-table::
       :class: no-outer-border
       :widths: 20 80
 
       * - |xmark| **Read own writes**
 
-        - Read\ :sub:`1` reads data from ``S``\ :sub:`2` that does not
+        - Read\ :sub:`1` reads data from ``S``\ :sub:`2` that doesn't
           reflect a state after Write\ :sub:`1`.
 
       * - |checkmark| **Monotonic reads**
 
         - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that reflects
-          a state after Read\ :sub:`1` (i.e. an earlier state is
+          a state after Read\ :sub:`1` (meaning that an earlier state is
           reflected in the data read by Read\ :sub:`1`).
 
       * - |xmark| **Monotonic writes**
@@ -340,11 +345,11 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state after Read\ :sub:`1` (i.e. an
+          reflects a state after Read\ :sub:`1` (meaning that an
           earlier state reflects the data read by Read\
           :sub:`1`).
 
-   |arrow| *If causal consistency does not imply durability*
+   |arrow| *If you want causal consistency without data durability*
 
    .. list-table::
       :class: no-outer-border
@@ -359,7 +364,7 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Monotonic reads**
 
         - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that reflects
-          a state after Read\ :sub:`1` (i.e. an earlier state is
+          a state after Read\ :sub:`1` (meaning that an earlier state is
           reflected in the data read by Read\ :sub:`1`).
 
       * - |checkmark| **Monotonic writes**
@@ -371,7 +376,7 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state after Read\ :sub:`1` (i.e. whose
+          reflects a state after Read\ :sub:`1` (meaning whose
           earlier state reflects the data read by Read\
           :sub:`1`).
 
@@ -409,21 +414,21 @@ provides the following causal consistency guarantees *if causal consistency impl
      :sub:`old` and ``S``\ :sub:`1`, and the two members sync from the
      other members of the replica set.
 
-   |arrow| *If causal consistency implies durability*
+   |arrow| *If you want causal consistency with data durability*
 
    .. list-table::
       :class: no-outer-border
       :widths: 20 80
 
       * - |xmark| **Read own writes**
 
-        - The data read by Read\ :sub:`1` does not reflect the results
+        - The data read by Read\ :sub:`1` doesn't reflect the results
           of Write\ :sub:`1`, which has rolled back.
 
       * - |checkmark| **Monotonic reads**
 
         - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that reflects
-          a state after Read\ :sub:`1` (i.e. whose
+          a state after Read\ :sub:`1` (meaning whose
           earlier state reflects the data read by Read\
           :sub:`1`).
 
@@ -436,10 +441,10 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state after Read\ :sub:`1` (i.e. whose
+          reflects a state after Read\ :sub:`1` (meaning whose
           earlier state reflects the data read by Read\ :sub:`1`).
 
-   |arrow| *If causal consistency does not imply durability*
+   |arrow| *If you want causal consistency without data durability*
 
    .. list-table::
       :class: no-outer-border
@@ -453,7 +458,7 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Monotonic reads**
 
         - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that reflects
-          a state after Read\ :sub:`1` (i.e. an earlier state
+          a state after Read\ :sub:`1` (meaning that an earlier state
           reflects the data read by Read\ :sub:`1`).
 
       * - |checkmark| **Monotonic writes**
@@ -465,8 +470,8 @@ provides the following causal consistency guarantees *if causal consistency impl
       * - |checkmark| **Writes follow reads**
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that
-          reflects a state after Read\ :sub:`1` (i.e. an earlier state
-          reflects the data read by Read\ :sub:`1`).
+          reflects a state after Read\ :sub:`1` (meaning that an 
+          earlier state reflects the data read by Read\ :sub:`1`).
 
 .. _causal-rc-local-wc-1:
 
@@ -524,9 +529,9 @@ some situations, but not necessarily in all situations.
 
       * - |xmark| Monotonic reads
 
-        - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that does not
-          reflect a state after Read\ :sub:`1` (i.e. an earlier state
-          does not reflect the data read by Read\ :sub:`1`).
+        - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that doesn't
+          reflect a state after Read\ :sub:`1` (meaning that an earlier 
+          state doesn't reflect the data read by Read\ :sub:`1`).
 
       * - |xmark| Monotonic writes
 
@@ -536,8 +541,9 @@ some situations, but not necessarily in all situations.
       * - |xmark| Write follow read
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that does
-          not reflect a state after Read\ :sub:`1` (i.e. an earlier
-          state does not reflect the data read by Read\ :sub:`1`).
+          not reflect a state after Read\ :sub:`1` (meaning that an 
+          earlier state doesn't reflect the data read by Read\ 
+          :sub:`1`).
 
 .. _causal-rc-local-wc-majority:
 
@@ -589,14 +595,14 @@ some situations, but not necessarily in all situations.
 
       * - |xmark| Read own writes.
 
-        - Read\ :sub:`1` reads data from ``S``\ :sub:`1` that does not
+        - Read\ :sub:`1` reads data from ``S``\ :sub:`1` that doesn't
           reflect a state after Write1\ :sub:`1`.
 
       * - |xmark| Monotonic reads.
 
-        - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that does not
-          reflect a state after Read\ :sub:`1` (i.e. an earlier state
-          does not reflect the data read by Read\ :sub:`1`).
+        - Read\ :sub:`2` reads data from ``S``\ :sub:`3` that doesn't
+          reflect a state after Read\ :sub:`1` (meaning that an earlier 
+          state doesn't reflect the data read by Read\ :sub:`1`).
 
       * - |checkmark| Monotonic writes
 
@@ -606,8 +612,9 @@ some situations, but not necessarily in all situations.
       * - |xmark| Write follow read.
 
         - Write\ :sub:`2` updates data on ``P``\ :sub:`new` that does
-          not reflect a state after Read\ :sub:`1` (i.e. an earlier
-          state does not reflect the data read by Read\ :sub:`1`).
+          not reflect a state after Read\ :sub:`1` (meaning that an 
+          earlier state doesn't reflect the data read by Read\ 
+          :sub:`1`).
 
 
 .. |arrow| unicode:: U+27A4