Which fields can the balance algorithm of ElasticSearch be applied to? (Multiple choice)

Question

Options

• AImport data
• BExport data
• CVolume reduction
• DExpansion

• A
  75% (47)
• B
  25% (16)

Explanation

Elasticsearch's balance algorithm governs how shards are distributed across cluster nodes, and it activates during data import (A), volume reduction (C), and cluster expansion (D) - all three are events that alter the shard distribution state and require rebalancing to maintain an even load. During import, incoming shards are allocated according to balance weights; during volume reduction (e.g., shard merging or index shrinking), the algorithm redistributes the remaining shards; during expansion (adding new nodes), it migrates shards to newly available nodes to equalize the load.

B (Export data) is incorrect because exporting is a read-only operation - it pulls data out of the cluster without changing shard placement, so the balancer has nothing to act on.

Memory tip: Think of the balance algorithm as a "cluster reshaper" - it only fires when the cluster's physical shape changes (more data in, less data stored, or more nodes available). Export just reads the existing shape without changing it, so it's the odd one out.

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