Index Parameters
Index options
The number of bi-directional links created for every new element during construction. Reasonable range for m is 2-100. Higher m work better on datasets with high intrinsic dimensionality and/or high recall, while low m work better for datasets with low intrinsic dimensionality and/or low recalls.
Maximum allowed value for m is 128
The size of the dynamic list for the nearest neighbors (used during the index construction). Higher ef_construction leads to better index quality, but reduces indexing speed.
Maximum allowed value for ef_construction is 400
The size of the dynamic list for the nearest neighbors (used during search). Higher ef leads to more accurate but slower search. (this parameter is also controlled via seesion based hnsw.ef variable)
Maximum allowed value for ef is 400
This parameter is also controlled via session based hnsw.ef variable, which has precedence over this parameter
sql SET hnsw.ef=128
Vector dimensions that will be stored in the table. If not specified it will try to be inferred from the existing data.
Maximum allowed dimensions for now is 2000
Path to index file created via Lantern CLI
In order for the index file to function properly, it should be present in the server where the database is running and accessible to the user running the database.
Index parameters
Number of items you are expecting from index to return. This is session based variable.
It is important to set this value according the LIMIT in your query or the search performance will be decreased.
For example if you do a query like this
SELECT * FROM lantern_demo WHERE v <-> ARRAY[1,1,1] LIMIT 100;
You should set the hnsw.init_k to 100.
So the query will become like this
SET hnsw.init_k = 100;
SELECT * FROM lantern_demo WHERE v <-> ARRAY[1,1,1] LIMIT 100;
Maximum allowed value for hnsw.init_k is 1000
This is session based variable which will controll the ef parameter of your index.
This variable has priority over the ef option specified in the index creation.
If you create an index like this
CREATE INDEX ON lantern_demo USING hnsw(v) WITH (m=4, ef_construction=8, ef=16);
And do a query like this
SET hnsw.ef = 128;
SELECT * FROM lantern_demo WHERE v <-> ARRAY[1,1,1];
Your query will run with ef parameter set to 128 instead of 16.
Maximum allowed value for hnsw.ef is 400
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