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commit 59d0840bad3cdeb57caa9bae4822733df99eb717
Author: Benoit Tellier <btell...@linagora.com>
AuthorDate: Thu Oct 17 09:15:30 2019 +0700
JAMES-2078 ADR for ElasticSearch disable dynamic mapping
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+# 9. Disable ElasticSearch dynamic mapping
+
+Date: 2019-10-10
+
+## Status
+
+Accepted (lazy consensus)
+
+## Context
+
+We rely on dynamic mappings to expose our mail headers as a JSON map. Dynamic
mapping is enabled for adding not yet encountered headers in the mapping.
+
+This causes a serie of functional issues:
+ - Maximum field count can easily be exceeded
+ - Field type 'guess' can be wrong, leading to subsequent headers omissions [1]
+ - Document indexation needs to be paused at the index level during mapping
changes to avoid concurrent changes, impacting negatively performance.
+
+## Decision
+
+Rely on nested objects to represent mail headers within a mapping
+
+## Consequences
+
+The index needs to be re-created. Document reIndexation is needed.
+
+This solves the aforementionned bugs [1].
+
+Regarding performance:
+ - Default message list performance is unimpacted
+ - We noticed a 4% performance improvment upon indexing throughput
+ - We noticed a 7% increase regarding space per message
+
+## References
+
+ - [1]: https://github.com/linagora/james-project/pull/2726 JAMES-2078 Add an
integration test to prove that dynamic mapping can lead to ignored header fields
+ - [JIRA](https://issues.apache.org/jira/browse/JAMES-2078)
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