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DOCSP-45863-embedded-verifier-migrations #557

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DOCSP-45863-embedded-verifier-migrations #557

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DOCSP-45863-embedded-verifier-migrations
ajhuh-mdb Jan 21, 2025
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10 changes: 10 additions & 0 deletions source/includes/fact-verifier-limitations.rst
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Expand Up @@ -37,6 +37,16 @@ Unsupported Verification Checks

.. include:: /includes/fact-verifier-unsupported

.. note::
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can we also include this note:

“Mongosync preserves document field-order based on what it reads using read preference primary from the source cluster. The embedded verifier will verify documents based on the source cluster’s primary node. It will not be able to verify discrepancies among the different source cluster nodes. In rare cases, discrepancies among the different source cluster’s nodes will cause the embedded verifier to fail a migration.”

at the top of the page? This applies to all migrations

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lgtm % changing In rare cases, discrepancies among the different source cluster’s nodes will cause the embedded verifier to fail a migration to In rare cases, discrepancies in document field order among the source cluster’s nodes will cause the embedded verifier to fail a migration even if mongosync copied documents correctly

It may also make sense to mention that the only case where this can happen is if an election occurs.

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can we note that this issue can only occur in rare cases?

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@ajhuh-mdb ajhuh-mdb Jan 24, 2025 •
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Just to double check my understanding is it that any time an election occurs this can happen or just a small portion of elections? Mainly want to make sure that we're clearing on distinguishing that if we're mentioning "rare cases" @ajayvijayakumar123 @rohshar

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Discrepancies among different source cluster nodes only happen in very rare cases. Even if there is a discrepancy, an election may not even surface the issue and cause the verifier to fail. I think we can just say that this issue is rare in general.


Starting in version 1.10, the verifier checks for data inconsistencies from
a :ref:`DDL event <c2c-older-version-limitations>` that occurred on the
pre-6.0 source cluster during migration. This is because pre-6.0 migrations
do not support DDL events.

To learn more, see :ref:`Pre-6.0 Migration Limitations
<c2c-older-version-limitations>`.

Unsupported Beta Features
~~~~~~~~~~~~~~~~~~~~~~~~~

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12 changes: 9 additions & 3 deletions source/reference/verification/embedded.txt
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Expand Up @@ -22,9 +22,15 @@ Verify with Embedded Verifier
of checks on the destination cluster to verify the sync of
supported collections.

.. important::

.. include:: /includes/fact-verifier-unsupported
.. note::

``mongosync`` reads using :readmode:`primary` read preference, so it
preserves document field order from the source cluster's primary node. The
embedded verifier also checks documents based on the source cluster’s primary
node, but at a different time from when ``mongosync`` reads them. Because of
this, in rare cases, discrepancies in document field order between the source
cluster’s nodes can cause the embedded verifier to fail the migration, even
if ``mongosync`` copied the documents correctly.

.. versionadded:: 1.9

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