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DOCSP-23935 Disaster Recovery update (#83)
* DOCSP-23935 Scrubs mention of 'capped collections' * DOCSP-23935 Title fix * DOCSP-23935 Updates introduction * DOCSP-23935 Introduction fixes * DOCSP-23935 Fixes per Ashley * DOCSP-23935 Titleline fix * DOCSP-23935 Fixes per Lingzhi * DOCSP-23935 Table fix
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source/reference.txt

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/reference/mongosync-states
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/reference/oplog-sizing
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/reference/configuration
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/reference/failure-recovery
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/reference/disaster-recovery
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/reference/limitations
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source/reference/failure-recovery.txt renamed to source/reference/disaster-recovery.txt

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.. _c2c-failure-recovery:
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==========================
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Recovery From Sync Failure
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==========================
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=======================================
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Use ``mongosync`` for Disaster Recovery
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=======================================
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.. default-domain:: mongodb
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:depth: 2
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:class: singlecol
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Setting up {+c2c-product-name+} to prepare for disaster recovery follows the
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same procedure as other :ref:`connections <c2c-connecting>` between clusters.
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Synchronization keeps the destination cluster up to date with the source
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cluster and ready as a backup. In the event that the source cluster fails or
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becomes otherwise unavailable, the destination cluster can replace it as the
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primary cluster.
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:program:`mongosync` temporarily alters some collection characteristics
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during synchronization. The original values are restored during the
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:ref:`commit process <c2c-api-commit>`. However, a permanent system
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failure could disrupt synchronization before the sync is committed. If
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the sync ends prematurely, you must manually reset the collection
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characteristics on the destination cluster.
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:ref:`commit process <c2c-api-commit>`. If synchronization ends prematurely,
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you must manually reset these collection characteristics on the destination
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cluster before you can use it as the primary cluster.
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To prepare the destination cluster to replace the source cluster, make the
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following changes:
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.. list-table::
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:header-rows: 1
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* - Change
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- Description
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* - :ref:`Unique Indexes <c2c-dr-unique>`
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- Unique indexes on the source cluster synchronize as non-unique indexes
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on the destination cluster.
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Indexes that should be unique must be manually set to unique.
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* - :ref:`TTL Indexes <c2c-dr-ttl>`
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- Synchronization sets ``expireAfterSeconds`` to the value of ``MAX_INT``
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on the destination cluster.
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Manually revert the following temporary changes:
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Use the :dbcommand:`collMod` command to set ``expireAfterSeconds``
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to the desired value.
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* - :ref:`Hidden Indexes <c2c-dr-hidden>`
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- Synchronization replicates hidden indexes as non-hidden.
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Use the :dbcommand:`collMod` command to hide any indexes that should
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be hidden.
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* - :ref:`Write Blocking <c2c-dr-write-blocking>`
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- ``mongosync`` can disable writes on the destination cluster.
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If synchronization was started with write blocking, disable the Write
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Block Mode.
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- :ref:`Unique indexes set as non-unique <c2c-dr-unique>`
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- :ref:`TTL indexes with expireAfterSeconds set to MAX_INT
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<c2c-dr-ttl>`
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- :ref:`Hidden indexes set as non-hidden <c2c-dr-hidden>`
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- :ref:`Capped collections with size/max set to the maximum possible
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value <c2c-dr-capped>`
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- :ref:`Write blocking <c2c-dr-write-blocking>`
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.. _c2c-dr-unique:
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transient uniqueness violations on the destination cluster. To avoid
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these errors, unique indexes are replicated as non-unique. If
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synchronization ends early, manually resolve any uniqueness violations
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and convert the non-unique indexes back to unique indexes.
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and convert any non-unique indexes that should be unique into unique indexes.
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Prepare the Index for Conversion
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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not hidden on the destination cluster. Use the ``collMod`` command to
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hide indexes that should be hidden.
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.. _c2c-dr-capped:
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Capped Collections
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------------------
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During synchronization, :ref:`capped collections
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<manual-capped-collection>` are set to the maximum allowable size. Use
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the ``collMod`` command to set the correct maximum size.
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.. _c2c-dr-write-blocking:
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Write blocking

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