pingcap/tidb

Avoid double-copy buffer when responding MySQL packets

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#32,097 opened on Feb 3, 2022

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help wantedtype/enhancementtype/performance

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Description

Enhancement

When we want to return the packages to the client, our logic is:

  1. Prepare the packet and serialize it to a buffer allocated by the area.Allocator
  2. Write this data through packetIO.WritePacket, in the WritePacket, the data will be cached in a buffer writer
  3. Flush the buffer writer to the connection

Mostly, e.g, for write ok https://github.com/pingcap/tidb/blob/0c19f927419f6b043a345e4a2af5336272830229/server/conn.go#L1442, we can see that we don't need to double copy the buffer, we can serialize the data and write it directly to the connection.

Contributor guide

Research direction
Investigate the serialization path in server/conn.go to directly write to connection without intermediate buffer.
Tech stack
go
Domain
backend
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60