This issue is included in MongoDB System Alert: Sharded multi-document transactions may perform operations using inconsistent sharding metadata. The information below describes only the behavior and impact related to SERVER-77506. Please see the consolidated issue page for guidance on identifying if you are impacted by these issues and remediation

SUMMARY

Operations within a multi-document transaction may not correctly read or be applied to documents if they occur on ranges of data that undergo a chunk/range migration during the transaction. Reads may return incomplete results, and update or delete operations may not be applied to documents subject to the range/chunk migration.

ISSUE DESCRIPTION AND IMPACT

During the course of a multi-document transaction on a Sharded collection, ranges of data that migrated concurrently may not be visible to the transaction nor detected as conflicting writes. This ultimately manifests as operations spanning more than one shard, potentially missing reads and writes.

This behavior only affects multi-document transactions using a Read Concern of 'local' (default for reads) or 'majority'. Multi-document transactions using read concern of 'snapshot' are not affected.

This issue affects MongoDB versions:

• MongoDB 4.4.0 through 4.4.27
• MongoDB 5.0.0 through 5.0.23
• MongoDB 6.0.0 through 6.0.12
• MongoDB 7.0.0 through 7.0.2
• MongoDB 7.1.0 - 7.1.1

The minimum conditions for the issue to manifest (all must be met) are:

• Sharded Cluster with more than one shard;
• Balancer is enabled;
• A multi-statement transaction, that:
  • Runs at local (default for reads) or majority read concern, and
  • Performs operations on two or more collections, where the second (or later) collection that receives operations is sharded; and
• A chunk migration for the second (or later) collection is committed after the first statement of the transaction has started running.

The issue occurs because, under these conditions, it is incorrectly possible for the recipient of a chunk migration to perform operations on an earlier state of the data. When this happens, those operations match no documents and become no-ops even though the recipient has received the documents and owns their chunk range.

The table below describes which types of operations may be impacted and how:

WORKAROUND

If your workload utilizes multi-document transactions on a Sharded cluster meeting the criteria above, we recommend that you:

• Disable the sharded cluster balancer.
• Upgrade to MongoDB 4.4.28, 5.0.24, 6.0.13 or 7.0.3.
• Re-enable the balancer.
• See the Diagnosis & Remediation section below.

DIAGNOSIS & REMEDIATION

See MongoDB System Alert: Sharded multi-document transactions may perform operations using inconsistent sharding metadata for guidance on assessing if you are impacted and the recommended remediation steps.