Hi All I have some questions about the memory usage. I would really appreciate if someone can help answer these.
I understand from the docs that during reading/querying, Lucene uses MMapDirectory (assuming it is supported on the platform). So the Java heap overhead in this case will purely come from the objects that are allocated/instantiated on the query path to process the query and build results etc. But the whole index itself will not be loaded into memory because we memory mapped the file. Is my understanding correct? In this case, we are better off not increasing the Java heap and keep as much as possible available for the file system cache for mmap to do its job efficiently. However, are there any portions of index structures that are completely loaded in memory regardless of whether it is MMapDirectory or not? If so, are they loaded in Java heap or do we use off-heap (direct buffers) in such cases? Secondly, on the write path I think even though the writer opens a MMapDirectory, the writes are gathered/buffered in memory upto a flush threshold controlled by IndexWriterConfig. Is this buffering done in Java heap or direct memory? Thanks a lot for help Siddharth
