Batch inserts can potentially yield after each single insert. This can negatively impact performance and is inconsistent with the yield policy of batch updates and deletes, which check less frequently.
Bulk insert tasks have a noticeable performance penalty compared to previous versions of MongoDB.
An older version of the driver that does not use the write commands is unaffected by this issue and can be used as a workaround with MongoDB 2.6.0.
Changing the yielding policy to the same as updates/deletes (allow yields less frequently) improves insert performance significantly (by ~28% in internal tests).
Version 2.6.0 is affected by this bug.
The patch is included in the 2.6.1 production release.