charset: fix incorrect result when querying in-txn updates when new collation is enabled #18703
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The decoding status can be tracked by the type system. This can help prevent bugs such as the one fixed here: pingcap#18703
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What problem does this PR solve?
Issue Number: close #18702
Problem Summary:
In TiDB, an uncommitted update within an ongoing transaction is saved in a memory buffer. When read by the ongoing transaction, the value in the memory buffer is supposed to be returned. However, for a column with new collation(when the config
new_collations_enabled_on_first_bootstrapis set to true) and the ongoing transaction is reading the uncommitted update with a unique index, the value is wrongly decoded. As a result, the uncommitted update is not included in the result and thus causes the bug.What is changed and how it works?
What's Changed and how it works:
The
DecodeIndexHandleis used to decode the handle from the index value in the memory buffer, fix it by adding support for the new collation:tidb/executor/mem_reader.go
Line 350 in 1077b04
Check List
Tests
See the charset: incorrect result when querying in-txn updates when new collation is enabled #18702
Side effects
Release note