On 1/3/23 02:53, Bram Van Dam wrote:
For a bit more context: we noticed that without docValues, the unique key field ends up wasting gigabytes of memory per core (in field cache, iirc). One entry per unique identifier. Regardless of whether or not the core is even being hit. With docValues enabled, this is ameliorated. This was pretty painful in large cloud instances with many large shards in memory constrained environments.
Yep, that is exactly the problem that docValues solves. Instead of the data structure that advanced features need being built in the heap, it is just read from disk using MMAP. It still will consume memory, but that's in the form of the OS disk cache, which under "normal" circumstances can be instantly reclaimed by the OS if it is needed. The docValues data structure is NOT allocated in the Solr heap, so the heap can be smaller, which helps GC performance.
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