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https://issues.apache.org/jira/browse/HBASE-26460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17445282#comment-17445282
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Duo Zhang commented on HBASE-26460:
-----------------------------------
For ByteBuf, netty uses reference counting to manager its lifecycle, so I think
even if we call release when closing the channel, we should still have a
reference in the ipc handler if it is still in use?
> Close netty channel causes regionserver crash in handleTooBigRequest
> --------------------------------------------------------------------
>
> Key: HBASE-26460
> URL: https://issues.apache.org/jira/browse/HBASE-26460
> Project: HBase
> Issue Type: Bug
> Components: rpc
> Affects Versions: 3.0.0-alpha-1, 2.0.0
> Reporter: Xiaolin Ha
> Assignee: Xiaolin Ha
> Priority: Critical
>
> In HBASE-26170, I proposed the coredump problem after calling
> handleTooBigRequest, but that issue did not resolve the regionserver crash
> problem, which occurs before the WAL corruption in HBASE-24984.
> After looking through the codes, I think the problem is in CLOSE channel.
> The direct byte buffer used by RPC call request is allocated by Netty, though
> we add a reference count to record when to release the direct byte buffer,
> the byte buffer is managed by Netty actually. It is allocated from Netty
> PoolArena, and is released there.
> When the HBase ipc handler is processing a request, the Netty channel handler
> can process the channel events and message coming back in succession. When
> there is a too big request by NettyRpcFrameDecoder, the channel will be
> closed, and all the resources of the channel will be released, though there
> is HBase ipc handlers using the direct byte buffer to process previous
> requests.
> Netty provides two methods to request the pooled byte buffer, one is through
> the PoolThreadCache, each handler thread owns a private one. Another is
> through PoolArena#allocateNormal. Each ChannelHandler has a local
> PoolThreadCache.
> When a new Netty channel is created, a new ChannelHandler instance is
> created.
> And when a channel is closed, the relevant channel handler will be removed
> from the pipeline. I found this annotation in the Channel class of Netty,
> {code:java}
> It is important to call close() or close(ChannelPromise) to release all
> resources once you are done with the Channel. This ensures all resources are
> released in a proper way, i.e. filehandles. {code}
> And when channel handler is removed in ByteToMessageDecoder#handlerRemoved,
> it will release the byte buffer,
> {code:java}
> @Override
> public final void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
> if (decodeState == STATE_CALLING_CHILD_DECODE) {
> decodeState = STATE_HANDLER_REMOVED_PENDING;
> return;
> }
> ByteBuf buf = cumulation;
> if (buf != null) {
> // Directly set this to null so we are sure we not access it in any
> other method here anymore.
> cumulation = null;
> int readable = buf.readableBytes();
> if (readable > 0) {
> ByteBuf bytes = buf.readBytes(readable);
> buf.release();
> ctx.fireChannelRead(bytes);
> } else {
> buf.release();
> }
> ... {code}
> We should not close the channel when encountering too big request, I think it
> should just skip the bytes like that in LengthFieldBasedFrameDecoder.
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