Metrics for replica sync - ES 7.0.1

Elastic Stack Elasticsearch
1

Are there any specific metrics which indicate if the replica shards are out of sync wrt primary shards.

I checked something which appears relatively closer from _cat/shards API

seq_no.global_checkpoint , sqg , globalCheckpoint - Global checkpoint.
seq_no.local_checkpoint , sql , localCheckpoint - Local checkpoint

But I was looking for some metric which is derived from checkpoint values which would be more on lines of List of shards which are currently out of sync with their corresponding primaries

Are there any such direct out-of-sync metrics available or in case no such direct metrics are available,

  1. Is it logical to derive from above checkpoint values shardwise ?
  2. What is the exact way of deriving the same from checkpoint values ?

Thanks in advance

  • dinesh
2

Running replicas are never out-of-sync with the primary, so it's not really clear what you're trying to do here.

3

@DavidTurner,

Since the replication is asynchronous (as I understand clients are ack'd for writes by ES after primary shards complete local translog persistence), would there no be possibility of replica not being able to catch-up with primary due to factors like long-pause GCs even when the cluster is in steady state - even without HA conditions like recovery ?

-dinesh

4

Replication is synchronous: indexing is not acked until all active shard copies have persisted the operations.

5

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