[BUG] Optimising hashmap.get call inside AwarenessAllocationDecider

[RS146BIJAY]

Describe the bug

Description

HashMap.get function call for a hash map where key is String is a relatively costly operation. AwarenessAllocationDecider makes multiple HashMap.get to

• Check if this Attribute value is set for this node.
• Fetch Awareness attribute value on which allocation of a shard is determined for a node,
• Calculate total shard count per attribute inside underCapacity function.

This makes HashMap.get function calls as most costly operation in AwarenessAllocationDecider which itself takes about 20% of total time for initialising 225k shards on 500 nodes.

Related component

Indexing:Replication

To Reproduce

Create 500k shards on a setup with 1000 data nodes and 3 master nodes.

Expected behavior

Optimises AwarenessAllocationDecider by reducing HashMap.get and HashMap.merge function calls.

Additional Details

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• OS: [e.g. iOS]
• Version [e.g. 22]

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