Summary

This chapter addressed some common performance and reliability issues that come up when using Elasticsearch. To reiterate some of the major points in this chapter:

• Always double-check your Elasticsearch cluster's configuration for errors

• Set the fielddata cache size, especially if you see OutOfMemoryError exceptions

• Use the slow log to find what queries run slow on your cluster

• Avoid aggregations on high-cardinality fields (such as millisecond timestamps)

• Be cognizant of your data indexing strategy so that no one index grows too large

• Use index warmers or enable eager_global_ordinals to ensure queries that use the fielddata cache are fast the first time we run them

• If possible, use SSDs on nodes that index data, and avoid storing Elasticsearch indices on network storage

Most importantly, when diagnosing Elasticsearch issues, be meticulous about testing at each stage. For example, don't try to optimize a query by making changes to elasticsearch.yml, modifying the query criteria, and enabling...