45 lines
1.9 KiB
Plaintext
45 lines
1.9 KiB
Plaintext
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[role="xpack"]
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[testenv="platinum"]
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[[ccr-requirements]]
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=== Requirements for leader indices
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beta[]
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Cross-cluster replication works by replaying the history of individual write
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operations that were performed on the shards of the leader index. This means that the
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history of these operations needs to be retained on the leader shards so that
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they can be pulled by the follower shard tasks. The underlying mechanism used to
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retain these operations is _soft deletes_. A soft delete occurs whenever an
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existing document is deleted or updated. By retaining these soft deletes up to
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configurable limits, the history of operations can be retained on the leader
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shards and made available to the follower shard tasks as it replays the history
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of operations.
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Soft deletes must be enabled for indices that you want to use as leader
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indices. Enabling soft deletes requires the addition of some index settings at
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index creation time. You must add these settings to your create index
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requests or to the index templates that you use to manage the creation of new
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indices.
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IMPORTANT: This means that {ccr} can not be used on existing indices. If you have
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existing data that you want to replicate from another cluster, you must
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{ref}/docs-reindex.html[reindex] your data into a new index with soft deletes
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enabled.
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[float]
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[[ccr-overview-soft-deletes]]
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==== Soft delete settings
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`index.soft_deletes.enabled`::
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Whether or not soft deletes are enabled on the index. Soft deletes can only be
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configured at index creation and only on indices created on or after 6.5.0. The
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default value is `false`.
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`index.soft_deletes.retention.operations`::
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The number of soft deletes to retain. Soft deletes are collected during merges
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on the underlying Lucene index yet retained up to the number of operations
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configured by this setting. The default value is `0`.
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For more information about index settings, see {ref}/index-modules.html[Index modules].
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