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default	Settings	k-NN	6

k-NN settings

The k-NN plugin adds several new index and cluster settings.

Index settings

The default values work well for most use cases, but you can change these settings when you create the index.

Setting	Default	Description
`index.knn.algo_param.ef_search`	512	The size of the dynamic list used during k-NN searches. Higher values lead to more accurate but slower searches.
`index.knn.algo_param.ef_construction`	512	The size of the dynamic list used during k-NN graph creation. Higher values lead to a more accurate graph, but slower indexing speed.
`index.knn.algo_param.m`	16	The number of bidirectional links that the plugin creates for each new element. Increasing and decreasing this value can have a large impact on memory consumption. Keep this value between 2-100.
`index.knn.space_type`	"l2"	The vector space used to calculate the distance between vectors. Currently, the k-NN plugin supports the `l2` space (Euclidean distance) and `cosinesimil` space (cosine similarity). For more information on these spaces, see the nmslib documentation.

Cluster settings

Setting	Default	Description
`knn.algo_param.index_thread_qty`	1	The number of threads used for graph creation. Keeping this value low reduces the CPU impact of the k-NN plugin, but also reduces indexing performance.
`knn.cache.item.expiry.enabled`	false	Whether to remove graphs that have not been accessed for a certain duration from memory.
`knn.cache.item.expiry.minutes`	3h	If enabled, the idle time before removing a graph from memory.
`knn.circuit_breaker.unset.percentage`	75.0	The native memory usage threshold for the circuit breaker. Memory usage must be below this percentage of `knn.memory.circuit_breaker.limit` for `knn.circuit_breaker.triggered` to remain false.
`knn.circuit_breaker.triggered`	false	True when memory usage exceeds the `knn.circuit_breaker.unset.percentage` value.
`knn.memory.circuit_breaker.limit`	50%	The native memory limit for graphs. At the default value, if a machine has 100 GB of memory and the JVM uses 32 GB, the k-NN plugin uses 50% of the remaining 68 GB (34 GB). If memory usage exceeds this value, k-NN removes the least recently used graphs.
`knn.memory.circuit_breaker.enabled`	true	Whether to enable the k-NN memory circuit breaker.
`knn.plugin.enabled`	true	Enables or disables the k-NN plugin.