125 lines
4.5 KiB
Plaintext
125 lines
4.5 KiB
Plaintext
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[[shards-allocation]]
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=== Cluster Level Shard Allocation
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Shard allocation is the process of allocating shards to nodes. This can
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happen during initial recovery, replica allocation, rebalancing, or
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when nodes are added or removed.
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[float]
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=== Shard Allocation Settings
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The following _dynamic_ settings may be used to control shard allocation and recovery:
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`cluster.routing.allocation.enable`::
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+
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--
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Enable or disable allocation for specific kinds of shards:
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* `all` - (default) Allows shard allocation for all kinds of shards.
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* `primaries` - Allows shard allocation only for primary shards.
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* `new_primaries` - Allows shard allocation only for primary shards for new indices.
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* `none` - No shard allocations of any kind are allowed for any indices.
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This setting does not affect the recovery of local primary shards when
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restarting a node. A restarted node that has a copy of an unassigned primary
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shard will recover that primary immediately, assuming that the
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<<index.recovery.initial_shards,`index.recovery.initial_shards`>> setting is
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satisfied.
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--
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`cluster.routing.allocation.node_concurrent_recoveries`::
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How many concurrent shard recoveries are allowed to happen on a node.
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Defaults to `2`.
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`cluster.routing.allocation.node_initial_primaries_recoveries`::
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While the recovery of replicas happens over the network, the recovery of
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an unassigned primary after node restart uses data from the local disk.
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These should be fast so more initial primary recoveries can happen in
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parallel on the same node. Defaults to `4`.
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`cluster.routing.allocation.same_shard.host`::
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Allows to perform a check to prevent allocation of multiple instances of
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the same shard on a single host, based on host name and host address.
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Defaults to `false`, meaning that no check is performed by default. This
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setting only applies if multiple nodes are started on the same machine.
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`indices.recovery.concurrent_streams`::
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The number of network streams to open per node to recover a shard from
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a peer shard. Defaults to `3`.
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`indices.recovery.concurrent_small_file_streams`::
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The number of streams to open per node for small files (under 5mb) to
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recover a shard from a peer shard. Defaults to `2`.
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[float]
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=== Shard Rebalancing Settings
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The following _dynamic_ settings may be used to control the rebalancing of
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shards across the cluster:
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`cluster.routing.rebalance.enable`::
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--
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Enable or disable rebalancing for specific kinds of shards:
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* `all` - (default) Allows shard balancing for all kinds of shards.
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* `primaries` - Allows shard balancing only for primary shards.
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* `replicas` - Allows shard balancing only for replica shards.
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* `none` - No shard balancing of any kind are allowed for any indices.
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--
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`cluster.routing.allocation.allow_rebalance`::
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--
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Specify when shard rebalancing is allowed:
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* `always` - (default) Always allow rebalancing.
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* `indices_primaries_active` - Only when all primaries in the cluster are allocated.
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* `indices_all_active` - Only when all shards (primaries and replicas) in the cluster are allocated.
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--
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`cluster.routing.allocation.cluster_concurrent_rebalance`::
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Allow to control how many concurrent shard rebalances are
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allowed cluster wide. Defaults to `2`.
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[float]
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=== Shard Balancing Heuristics
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The following settings are used together to determine where to place each
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shard. The cluster is balanced when no allowed action can bring the weights
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of each node closer together by more then the `balance.threshold`.
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`cluster.routing.allocation.balance.shard`::
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Defines the weight factor for shards allocated on a node
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(float). Defaults to `0.45f`. Raising this raises the tendency to
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equalize the number of shards across all nodes in the cluster.
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`cluster.routing.allocation.balance.index`::
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Defines a factor to the number of shards per index allocated
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on a specific node (float). Defaults to `0.55f`. Raising this raises the
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tendency to equalize the number of shards per index across all nodes in
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the cluster.
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`cluster.routing.allocation.balance.threshold`::
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Minimal optimization value of operations that should be performed (non
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negative float). Defaults to `1.0f`. Raising this will cause the cluster
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to be less aggressive about optimizing the shard balance.
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NOTE: Regardless of the result of the balancing algorithm, rebalancing might
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not be allowed due to forced awareness or allocation filtering.
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