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Posted to notifications@shardingsphere.apache.org by "ShayneLee8 (via GitHub)" <gi...@apache.org> on 2024/10/18 06:18:17 UTC
[I] Getting wrong results when using "explain sql" in Sharding-Proxy 5.5.0, database is MySQL 5.7 [shardingsphere]
ShayneLee8 opened a new issue, #33292:
URL: https://github.com/apache/shardingsphere/issues/33292
Sharding-Proxy 5.5.0
Mysql 5.7
this is sharding config
Using explain
Without explain
When I don't have "explain" I get the correct STORAGE UNIT,
When I add "explain" I get the wrong STORAGE UNIT, why is this happening,
I want to get the correct ds_2, how can I do it
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Re: [I] Getting wrong results when using "explain sql" in Sharding-Proxy 5.5.0, database is MySQL 5.7 [shardingsphere]
Posted by "terrymanu (via GitHub)" <gi...@apache.org>.
terrymanu commented on issue #33292:
URL: https://github.com/apache/shardingsphere/issues/33292#issuecomment-3640525784
## Issue Understanding
- Sharding-Proxy 5.5.0 + MySQL 5.7, sharding algorithm ds_${ monthtime >= '2024-10' ? 2:0 }. A plain SELECT ... WHERE monthtime='2024-10' routes to ds_2, but adding EXPLAIN returns ds_0. You want the proxy to show the correct shard.
## Root Cause
- In the proxy, EXPLAIN is parsed as a DAL statement and routed via unicast (no sharding condition evaluation), typically choosing the first or current connection’s data source. This is by design and not a sharding-aware preview.
## Analysis
- To inspect sharding routing and rewritten SQL at the proxy layer, use DistSQL PREVIEW <SQL> instead of EXPLAIN. Official doc: docs/document/content/user-manual/shardingsphere-proxy/distsql/syntax/rul/preview-sql.en.md.
- PREVIEW returns data_source_name and actual_sql, so you can see ds_2 and the rewritten SQL. For the physical execution plan, run EXPLAIN directly on the target shard.
- The master branch still treats EXPLAIN as DAL unicast; no change there yet.
## Conclusion
- This is expected behavior, not a fixed bug. Use DistSQL PREVIEW SELECT ... to view routing in the proxy, and run EXPLAIN on the target shard to see the execution plan.
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Re: [I] Getting wrong results when using "explain sql" in Sharding-Proxy 5.5.0, database is MySQL 5.7 [shardingsphere]
Posted by "terrymanu (via GitHub)" <gi...@apache.org>.
terrymanu closed issue #33292: Getting wrong results when using "explain sql" in Sharding-Proxy 5.5.0, database is MySQL 5.7
URL: https://github.com/apache/shardingsphere/issues/33292
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