246 SnapshotUnavailable: SnapshotUnavailable

What does it mean?

A read with the requested snapshot read concern (readConcern: snapshot) could not be performed because the server cannot provide a consistent snapshot for that point in time. It is usually related to a read timestamp that has not advanced far enough or has fallen behind.

Why does it happen?

readConcern 'snapshot' is used (mostly in multi-document transactions) but a consistent view for the requested atLeast/at timestamp is not yet available; e.g. a newly created collection/index, a catalog change, or replication lag. The server rejects the read in this case.

How to fix it

This is usually transient; retry the operation after a short delay (the driver's transient transaction error retry mechanism covers this). If you recently ran DDL (collection/index creation), start the transaction after it. Check replication lag and node health. If a snapshot read is not truly needed, choose a more suitable readConcern.