276 IndexBuildAborted: IndexBuildAborted

What does it mean?

An in-progress index build was aborted/stopped before completion. The target index was not created successfully.

Why does it happen?

The index build may have been aborted due to insufficient disk/memory on the node, an explicit abort via dropIndexes, a primary step-down/replica state change, a uniqueness violation (conflicting documents while building a unique index), or a node restart.

How to fix it

Find the abort reason in the mongod logs (disk space, memory, uniqueness conflict, etc.) and resolve it. If you are building a unique index, clean up conflicting documents first. Provide sufficient disk/memory and make sure the replica state is stable. After fixing the issue, rebuild the index with createIndex; on large collections choose a low-load period.