ESRally Metrics Definition

I am working with ESRally and would like to understand what the various metrics mean. I tried reading the documentation provided here:, but it does not convey details such as what segment merging is, what is the flush time and why are these values even chosen as a metric to indicate performance.

Any pointers?

Hi @sanketshinde,

to the meaning of the individual metrics: the documentation only explains on a high-level and admittedly assume a detailed understanding of the inner workings of Elasticsearch. Btw, there is also that explains the raw metrics that Rally uses to create the summary report.

IMHO the primary metrics to look at are the request-related metrics: throughput (e.g. for bulk indexing operations) and service time or latency (for latency-sensitive operations like queries). The other metrics serve as secondary metrics to better understand where Elasticsearch spent time during indexing: was it busy merging a lot of segments, where merges throttled for a long time (disk issues?) etc. I think these can just serve as a first indication and once you see high values you need to dig further anyway with other tools like iostat, vmstat, a Java profiler, ... .


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Thanks for the pointers.

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