View source for Change Feed Estimator

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'''Category:''' Optimization

'''Summary:''' Reports pending change feed lag to help decide when to scale out consumer instances.

== Overview ==
The change feed estimator is a tool provided by the Azure Cosmos DB SDK's change feed processor that reports how many changes are pending to be processed (the 'lag') by change feed consumers, helping you determine whether you need to scale out the number of change feed processor instances to keep up with the rate of incoming changes.

== More Info & Links ==
* [https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/how-to-use-change-feed-estimator Microsoft Learn: Change feed estimator]

== DP-420 Style Practice Questions ==
'''Q1.''' What does the change feed estimator help you determine?
* A. How many unprocessed changes ('lag') remain, to decide if you should scale out consumer instances
* B. The RU cost of a specific query
* C. The consistency level of the account
* D. The maximum logical partition size

'''Q2.''' What might a growing lag reported by the change feed estimator indicate?
* A. Consumers are falling behind and may need additional change feed processor instances
* B. The container's indexing policy is misconfigured
* C. The partition key needs to be changed
* D. TTL is about to expire on many items

== Answer Key ==
''Answers are listed at the very end so you can attempt the questions first.''

* '''Q1 (Change Feed Estimator):''' A. How many unprocessed changes ('lag') remain, to decide if you should scale out consumer instances — The change feed estimator reports the backlog of unprocessed changes, guiding scale-out decisions for consumers.
* '''Q2 (Change Feed Estimator):''' A. Consumers are falling behind and may need additional change feed processor instances — A growing lag suggests the current number of change feed processor instances is insufficient to keep pace with incoming changes.

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''DP-420: Designing and Implementing Cloud-Native Applications Using Microsoft Azure Cosmos DB — term detail page''

[[Category:DP-420 Terminology]]
[[Category:Optimization]]