[IMPALA-10139] Slow RPC logs can be misleading - ASF JIRA

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Details

Type: Improvement
Status: Open
Priority: Major
Resolution: Unresolved
Affects Version/s: None
Fix Version/s: None
Component/s: Distributed Exec
Labels:
None

Epic Link:
Network Debugging / Supportability Improvements
Epic Color:
ghx-label-8

Description

The slow RPC logs added in ~~IMPALA-9128~~ are based on the total time taken to successfully complete a RPC. The issue is that there are many reasons why an RPC might take a long time to complete. An RPC is considered complete only when the receiver has processed that RPC.

The problem is that due to client-driven back-pressure mechanism, it is entirely possible that the receiver RPC does not process a receiver RPC because KrpcDataStreamRecvr::SenderQueue::GetBatch just hasn't been called yet (indirectly called by ExchangeNode::GetNext).

This can lead to flood of slow RPC logs, even though the RPCs might not actually be slow themselves. What is worse is that the because of the back-pressure mechanism, slowness from the client (e.g. Hue users) will propagate across all nodes involved in the query.