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33 changes: 19 additions & 14 deletions source/faq.txt
Original file line number Diff line number Diff line change
Expand Up @@ -26,20 +26,25 @@ following the steps in :ref:`c2c-reconfigure-mid-migration`.
Can I perform reads or writes to my destination cluster while ``mongosync`` is syncing?
---------------------------------------------------------------------------------------

You can perform reads at any time during synchronization.
However, ``mongosync`` combines and reorders writes from the source to destination during synchronization,
and also temporarily modifies various collection characteristics.
As a result, the destination is not guaranteed to match the source at any point in time when the sync is running.
For consistent reads, wait for the migration to :ref:`c2c-api-commit`. To learn more, see :ref:`mongosync-considerations`.

Performing writes to your destination cluster during synchronization results in undefined behavior.
``mongosync`` blocks writes on the destination cluster by default. To learn
more about write-blocking, see :ref:`c2c-write-blocking` and :ref:`c2c-api-start`.

Upon commit, it is only safe to write to the destination cluster when ``canWrite`` is ``true``.
To check the value of ``canWrite``, run the :ref:`c2c-api-progress` endpoint.

To learn more about permissable reads and writes during synchronization, see :ref:`c2c-reads-and-writes`.
``mongosync`` combines and reorders writes from the source to destination during
synchronization, and temporarily modifies various collection characteristics.
As a result, ``mongosync`` can't guarantee that the destination matches the
source, including a stale version of the source, at any point in time when the
sync is running. To safely accept traffic to the destination cluster, wait for
the migration to :ref:`c2c-api-commit`. To learn more, see
:ref:`mongosync-considerations`.

Performing writes to your destination cluster during synchronization results in
undefined behavior. ``mongosync`` blocks writes on the destination cluster by
default. To learn more about write-blocking, see :ref:`c2c-write-blocking` and
:ref:`c2c-api-start`.

Upon commit, it is only safe to write to the destination cluster when
``canWrite`` is ``true``. To check the value of ``canWrite``, run the
:ref:`c2c-api-progress` endpoint.

To learn more about permissable reads and writes during synchronization, see
:ref:`c2c-reads-and-writes`.

.. note::

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