Hello everyone, We recently added Java Flight Recorder (JFR) to our internal benchmarking. While looking through top heap allocations from JFR output, we noticed the following to be in top 5 contributors to garbage creation.
org.apache.lucene.store.IndexInput#getFullSliceDescription() at org.apache.lucene.store.ByteBufferIndexInput#buildSlice() at org.apache.lucene.store.ByteBufferIndexInput#slice() at org.apache.lucene.store.ByteBufferIndexInput$SingleBufferImpl#slice() at org.apache.lucene.store.IndexInput#randomAccessSlice() It seems that we construct a new String resource description for each clone/slice of IndexInput instance. Resource description for a clone/slice instance is a String concatenation of resource description from original instance and current slice description. Also, clone/slice can happen multiple times per query per segment. Can we avoid upfront String allocation by late-evaluating IndexInput.toString() on the cloned instance? One approach could be to hold a reference of the base IndexInput instance in the cloned instance. Then while evaluating IndexInput.toString() on a cloned instance, we can construct a resource description by concatenating base instance's toString() with current resource description. My understanding is that IndexInput.toString() is primarily used for debugging purposes hence we can benefit from the late-evaluation. With this approach, we are seeing sustainable GC time reduction of ~6% and gain of ~1% to red-line QPS (throughput). My intention to start this thread is to collect feedback on this approach as well as to discuss any other ideas. Thanks, Viral Gandhi
