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Migrating to 8.9

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Migrating to 8.9

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This section discusses the changes that you need to be aware of when migrating your application to Elasticsearch 8.9.

Breaking changes

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The following changes in Elasticsearch 8.9 might affect your applications and prevent them from operating normally. Before upgrading to 8.9, review these changes and take the described steps to mitigate the impact.

REST API changes

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Switch TDigestState to use HybridDigest by default

Details
The default implementation for TDigest in percentile calculations switches to a new internal implementation offering superior performance (2x-10x speedup), at a very small accuracy penalty for very large sample populations.

Impact
This change leads to generating slightly different results in percentile calculations. If the highest possible accuracy is desired, or it’s crucial to produce exactly the same results as in previous versions, one can either set execution_hint to high_accuracy in the tdigest spec of a given percentile calculation, or set search.aggs.tdigest_execution_hint to high_accuracy in cluster settings to apply to all percentile queries.

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