373c67dd7a
This is related to #27260. In Elasticsearch all of the messages that we serialize to write to the network are composed of heap bytes. When you read or write to a nio socket in java, the heap memory you passed down must be copied to/from direct memory. The JVM internally does some buffering of the direct memory, however it is essentially unbounded. This commit introduces a simple mechanism of buffering and copying the memory in transport-nio. Each network event loop is given a 64kb DirectByteBuffer. When we go to read we use this buffer and copy the data after the read. Additionally, when we go to write, we copy the data to the direct memory before calling write. 64KB is chosen as this is the default receive buffer size we use for transport-netty4 (NETTY_RECEIVE_PREDICTOR_SIZE). Since we only have one buffer per thread, we could afford larger. However, if we the buffer is large and not all of the data is flushed in a write call, we will do excess copies. This is something we can explore in the future. |
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