infearOnTheWay opened a new issue #2602: Add nio support for mysql protocal implementation URL: https://github.com/apache/incubator-doris/issues/2602 ### Description The motivation to add this feature originated from our own project. In order to make our service compatible with mysql protocal, we use related implementation in doris, which does help a lot! At the same time, we found that,each connection in doris would be assign a thread just for this connection, even if the connection is always idle. This make a centain amount of resource waste, while the max count of connections would be also limited since of thread stack size. We understand that the concurrency would expected to be not very high in doris currently, so such implmentation is simple and enough. On the other hand, we expect to support large amounts of connections in our condition. So we optimize the IO architechture in our project and would be appreciate to feedback this feature to doris, which would be a useful complementation in future. ### Solution We add another mysql server implementation based on XNIO framework. The details about XNIO could be get here [https://xnio.jboss.org/]. In shortly, XNIO can be treated as a very small but powerful io framework based on java nio. Underdow(a kind of container like tomcat or jetty) is also based on XNIO. In our implmentation, there exist two thread group:**io-thread** and **task-thread** .The io-thread focus on accepting all io-events.Since such handle is always fast, so the io-thread count can be a little small(equal to cpu core count is appreciate). On the other hand, we can add correspond callback to handle such events. For example, "accept listener" would be callback while connection reaches and "read listener" would be callback while any query on connection reaches. Such callback would be handled in task-thread asynchronously, since it is always cost a lot of time. All the connections would share these two thread groups, while there would be almost no blocking in the connecting and query phrase. ### Addtitional In our load test, max connection count could reach 100w+, while there still exist buffer on resources like cpu and memory. But we also found doris would pre-allocate a 2M byte buffer while every connection is established. Since this would occupy massive memory, we just changed the buffer size to 2K for test. We also do optimization on how to dynamicly allocate such part of buffer now. In fact, we do not refactor the core progress of connection and query logic in doris, and just do encapsulation above it. It should be noted that any threadlocal object(such as **ConnectContext**) should be deal with carefully since thread is not owned by each connection. Meanwhile, the **ConnectScheduler** is still used for connection management such as registration and idle check for new connect context. ps.This feature would enabled if the 'nio-enabled' config is set true.
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