[DiskBBQ] Hierarchical k-means recursion using temp files #133473
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Merging big segments in DIskBBQ on a small node can take a very long time. Flamegraphs shows lots of page faults during hierarchical k-means recursion, in particular when creating
FloatVectorValuesSlice:This PR explores the idea in which instead of slicing big off heap FloatVectorValues using
FloatVectorValuesSlice, we read all the data once and write the clusters (currently 128) into its own file. Recursion will process then one file at a time. First results show a nice improvement on memory constraint JVMs while little degradation when there is plenty of heap. The downside is data amplification as we need an extra copy of the vectors on disk.