Sort key libicu NIF#6050
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Add a sort key libicu NIF function. A sort key is an opaque binary representation generated by libicu from a key, which then can then be compared directly against other sort keys to produce an equivalent collation order as calling the pair-wise comparison libicu function. The idea to use sort keys in the fabric view row "merge head" structure, where we merge together streaming rows from multiple workers. When we do that we keep either a sorted list (for map-only views) and then do an insertion sort step and take the minimum, or we keep the rows in key/value structure for reduce views and find the minimum key and its grouped values. In either case we can reduce the number of libicu compare(a,b) calls from O(K^2) to just O(K) sort key generating calls and since libicu calls are not cheap, it worth adding an extra NIF calls just for it. As a side note: we've actually implemented this once during the now abandonned CouchDB 4.0 /w FoundationDB backed attempt, there we stored sort key in the database, which libicu workers do not recommend doing. Here we're planning on using in memory only on the coordinator. https://unicode-org.github.io/icu/userguide/collation/concepts#sortkeys-vs-comparison
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Add a sort key libicu NIF function. A sort key is an opaque binary representation generated by libicu from a key, which then can then be compared directly against other sort keys to produce an equivalent collation order as calling the pair-wise comparison libicu function.
The idea to use sort keys in the fabric view row "merge head" structure, where we merge together streaming rows from multiple workers. When we do that we keep either a sorted list (for map-only views) and then do an insertion sort step and take the minimum, or we keep the rows in key/value structure for reduce views and find the minimum key and its grouped values. In either case we can reduce the number of libicu compare(a,b) calls from O(K^2) to just O(K) sort key generating calls and since libicu calls are not cheap, it worth adding an extra NIF calls just for it.
As a side note: we've actually implemented this once during the now abandoned CouchDB 4.0 /w FoundationDB backed attempt, there we stored sort key in the database, which libicu workers do not recommend doing. Here we're planning on using in memory only on the coordinator.
https://unicode-org.github.io/icu/userguide/collation/concepts#sortkeys-vs-comparison