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DOCS-11447: Improve docs on linearizable read concern #3264

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Mar 16, 2018
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DOCS-11447: Improve docs on linearizable read concern #3264

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12 changes: 7 additions & 5 deletions source/includes/extracts-concurrency-consistency-recency.yaml
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Expand Up @@ -134,10 +134,12 @@ content: |
---
ref: no-journaling-rollback
content: |

With :rsconf:`writeConcernMajorityJournalDefault` set to ``false``,
MongoDB will not wait for
:writeconcern:`w: "majority" <"majority">` writes to be durable
before acknowledging the writes. As such, :writeconcern:`"majority"`
write operations could possibly
roll back in the event of a loss of a replica set member.
MongoDB does not wait for :writeconcern:`w: "majority" <"majority">`
writes to be written to the on-disk journal before acknowledging the
writes. As such, :writeconcern:`majority` write operations could
possibly roll back in the event of a transient loss (e.g. crash and
restart) of a majority of nodes in a given replica set.

...
17 changes: 10 additions & 7 deletions source/reference/read-concern.txt
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Expand Up @@ -94,13 +94,16 @@ The following read concern levels are available:

* - .. readconcern:: "linearizable"

- The query returns data that reflects all successful writes
issued with a write concern of :writeconcern:`"majority"` *and*
acknowledged prior to the start of the read operation. For
replica sets that run with
:rsconf:`writeConcernMajorityJournalDefault` set to true,
linearizable read concern returns data that will never be rolled
back.
- The query returns data that reflects all successful
majority-acknowledged writes that completed prior to the start
of the read operation. The query may wait for concurrently
executing writes to propagate to a majority of replica
set members before returning results.

If a majority of your replica set members crash and restart after
the read operation, documents returned by the read operation are
durable if :rsconf:`writeConcernMajorityJournalDefault` is set to
the default state of ``true``.

.. include:: /includes/extracts/no-journaling-rollback.rst

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