When a message is enqueued into a partitioned queue, service bus checks for the presence of a partition key. If it finds one, it selects the fragment based on the partition key.
But what happens when that fragment is full, there is no more space left in that fragment. Does service bus gives error/message is discarded or any other fragment will be used to store that message?
According to your description, I found some related content about fragment, you could refer to them:
If any of the fragments experience high traffic or the underlying store is unhealthy, those operations fail and availability is reduced.
As Messaging quotas states about Queue/topic size as follows:
Type: Defined upon creation of the queue/topic
Value: 1, 2, 3, 4 or 5 GB. If partitioning is enabled, the maximum queue/topic size is 80 GB.
Behavior when exceeded: Incoming messages will be rejected and an exception will be received by the calling code.
Additionally, you could add your feedback at GitHub issue Azure/azure-service-bus with the documentation label.
