ISSUE DESCRIPTION

This ticket consolidates information about a set of concurrency bugs that could result in the multikey metadata for an index being set incorrectly.
As a result, queries against multikey indexes can mistakenly treat the multikey index as a non-multikey index, and return query results containing individual elements rather than arrays containing those elements.

• SERVER-56877
• SERVER-41766
• SERVER-47694
• SERVER-47812

DIAGNOSIS AND IMPACT

The above tickets present similarly and their symptoms are not readily distinguishable from one another. They are identified by validate failures including messages like:

• "... multikey paths do not cover a document ..."
• "... is not multikey but document with RecordId ..."
• "... multikey paths do not cover a document with RecordId ..."

REMEDIATION AND WORKAROUNDS

• The recommended solution is to perform a logical initial sync on the affected node(s).
• The sync source is irrelevant; the index will be successfully rebuilt regardless of your selection.