Replicas

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The Replicas metric group contains metrics regarding the state of replicas in the cluster. The metrics available are:

  • ISR Expand Rate
  • ISR Shrink Rate
  • Under Min ISR Partitions
  • Under Replicated Partitions

ISR Expand Rate

The ISR Expand Rate metric displays the one minute rate and mean rate (per second) of increases in the number of In-Sync Replicas (ISR). ISR expansions occur when a broker comes online, such as when recovering from a failure or adding a new node. This increases the number of in-sync replicas available for each partition on that broker.

Expected value: 0

ISR Shrink Rate

The ISR Shrink Rate metric displays the one minute rate and mean rate (per second) of decreases in the number of In-Sync Replicas (ISR). ISR shrinks occur when an in-sync broker goes down, as it decreases the number of in-sync replicas available for each partition replica on that broker.

Expected value: 0

Under Min ISR Partitions

The Under Min ISR Partitions metric displays the number of partitions, where the number of In-Sync Replicas (ISR) is less than the minimum number of in-sync replicas specified. The two most common causes of under-min ISR partitions are that one or more brokers is unresponsive, or the cluster is experiencing performance issues and one or more brokers are falling behind.

Expected value: 0

Under Replicated Partitions

The Under Replicated Partitions metric displays the number of partitions that do not have enough replicas to meet the desired replication factor. A partition will also be considered under-replicated if the correct number of replicas exist, but one or more of the replicas have fallen significantly behind the partition leader. The two most common causes of under-replicated partitions are that one or more brokers is unresponsive, or the cluster is experiencing performance issues and one or more brokers have fallen behind.

Expected value: 0

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