60 lines
2.8 KiB
Plaintext
60 lines
2.8 KiB
Plaintext
[[breaking_50_allocation]]
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=== Allocation changes
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==== Primary shard allocation
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Previously, primary shards were only assigned if a quorum of shard copies were
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found (configurable using `index.recovery.initial_shards`, now deprecated). In
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case where a primary had only a single replica, quorum was defined to be a
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single shard. This meant that any shard copy of an index with replication
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factor 1 could become primary, even it was a stale copy of the data on disk.
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This is now fixed thanks to shard allocation IDs.
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Allocation IDs assign unique identifiers to shard copies. This allows the
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cluster to differentiate between multiple copies of the same data and track
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which shards have been active so that, after a cluster restart, only shard
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copies containing the most recent data can become primaries.
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==== Indices Shard Stores command
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By using allocation IDs instead of version numbers to identify shard copies
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for primary shard allocation, the former versioning scheme has become
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obsolete. This is reflected in the
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<<indices-shards-stores,Indices Shard Stores API>>.
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A new `allocation_id` field replaces the former `version` field in the result
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of the Indices Shard Stores command. This field is available for all shard
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copies that have been either created with the current version of Elasticsearch
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or have been active in a cluster running a current version of Elasticsearch.
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For legacy shard copies that have not been active in a current version of
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Elasticsearch, a `legacy_version` field is available instead (equivalent to
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the former `version` field).
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==== Reroute commands
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The reroute command `allocate` has been split into two distinct commands
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`allocate_replica` and `allocate_empty_primary`. This was done as we
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introduced a new `allocate_stale_primary` command. The new `allocate_replica`
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command corresponds to the old `allocate` command with `allow_primary` set to
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false. The new `allocate_empty_primary` command corresponds to the old
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`allocate` command with `allow_primary` set to true.
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==== Custom Reroute Commands
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Elasticsearch no longer supports plugins registering custom allocation
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commands. It was unused and hopefully unneeded.
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==== `index.shared_filesystem.recover_on_any_node` changes
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The behavior of `index.shared_filesystem.recover_on_any_node: true` has been
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changed. Previously, in the case where no shard copies could be found, an
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arbitrary node was chosen by potentially ignoring allocation deciders. Now, we
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take balancing into account but don't assign the shard if the allocation
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deciders are not satisfied.
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The behavior has also changed in the case where shard copies can be found.
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Previously, a node not holding the shard copy was chosen if none of the nodes
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holding shard copies were satisfying the allocation deciders. Now, the shard
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will be assigned to a node having a shard copy, even if none of the nodes
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holding a shard copy satisfy the allocation deciders.
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