flexsearch/doc/keystore.md

Big In-Memory Keystores

The default maximum keystore limit for the In-Memory index is 2^24 of distinct terms/partials being stored (cardinality). An additional register could be enabled and is dividing the index into self-balanced partitions. The extended keystore is supported by any type of index.

const index = new Index({
    // e.g. set keystore range to 8-Bit:
    // 2^8 * 2^24 = 2^32 keys total
    keystore: 8 
});

You can theoretically store up to 2^88 keys (64-Bit address range).

The internal ID arrays scales automatically when limit of 2^31 has reached by using Proxy.

Persistent storages has no keystore limit by default. You should not enable keystore when using persistent indexes, as long as you do not stress the buffer too hard before calling index.commit().

There is no additional memory cost when using a Keystore.