Messages will be stored on Event Hub for a specific time interval. Once this time expires messages are removed automatically. As offset values defines the position of event in the partition, I'm confused if I'll get the same offset value next time (after data expires from partition). If so then what is difference between offset and event sequence of partition?
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1 Answers
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TLDR: You will NEVER receive the same offset - even after the data is expired from EventHubs.
Offset: is the address (or pointer or cursor) of your Event on an EventHub Partition. Getting into implementation details, Offset is a struct on our Service (whose underlying value is stuffed into 64 bits - for optimization - and hence a c# long in the client) - representing the address of the event in our service's underlying file-system. If you need to replay the EventHub partition events from a particular point - you will need the Offset. That is exactly what it is built for.
SequenceNumber: is a monotonously increasing number that is STAMPED on every EventData - on Eventhubs Service - to represent the order of events. It is sequential and is intended be used to represent - length of the stream - no. of events on the Partition - by querying GetPartitionRuntimeInfo and diff. between LastEnqueuedSeqNo. and BeginSeqNo.. The receiver could get current received offset (from EventData.Offset) - which if you compare with LastEnqueuedSeqNo. can give - howmuch the receiver is lagging behind by - this is the prime reason why this was built for.
HTH! Sree
