server: retry executing sql without tiflash after tiflash is down #22459
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/cc @winoros |
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server/conn.go
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| if err != nil { | ||
| break | ||
| if terror.ErrorEqual(err, tikv.ErrTiFlashServerTimeout) && retryable { |
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It's better to introduce a switch(generally it is implemented as a SQL variable) to control if we retry here.
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PTAL @winoros |
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This was referenced Mar 23, 2021
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What problem does this PR solve?
Problem Summary:
When we get a backoff error of TiFlash, the SQL will always fail while the TiKV nodes are actually alive. We hope to fallback to TiKV after TiFlash is down.
What is changed and how it works?
Proposal: https://docs.google.com/document/d/1dgq1MZQigTcZeck0iRLSCAu_ly3iGDr19Et6IHfQhCs/edit?usp=sharing (This PR implements simple solution section)
What's Changed & How it Works:
When running
clientConn.handleQuery/clientConn.handleStmtExecute, if we getErrTiFlashServerTimeouterror and the execution of SQL does't have side effect (If TiDB server already sends data to client or the execution is in cursor mode, the execution has side effect), we delete TiFlash fromIsolationReadEngines, retry executing the SQL and add TiFlash back toIsolationReadEngines. Besides, we use a switchtidb_enable_tiflash_fallback_tikvto control whether to retry and the switch is off by default.Related changes
pingcap/docs/pingcap/docs-cn: system variable: add tidb_allow_fallback_to_tikv docs#4781 / system variable: add tidb_allow_fallback_to_tikv docs-cn#5484Check List
Tests
Release note