# TEMPLATE: Critical Bug [Add succinct description]

## Issue description

\[Insert description/symptoms/etc.\]

## Problem Details

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\[/example: \* When this problem is triggered, a mismatch between schema information and column data may result in the following symptoms, depending on the type of column change and the type of subsequent write operations:

\*\* Data access error "insufficient bytes to decode" is reported.

\* Error "Out of range value for column" is reported for data update.

\* No errors are reported for data access, but the data is incorrect, such as garbled characters or unexpected values.

\* After 'ADMIN CHECK TABLE' is executed, data and index consistency errors are reported.

/end example\]

## Steps to reproduce

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\[/example: For affected versions, if it is possible for a user to perform lossy column modification, notify the user that this operation is prohibited for the same column of a table in parallel. For details, see Solution to the problem of inconsistent table structure and data caused by concurrent column type changes on the same column ([https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#](https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#)) .

\* The TiDB version is v5.1.0 and above (refer to the impact version for details).

\* For the same column of a table, simultaneously perform something like "alter table tblName modify/change colName..." statement, and the statements executed are all lossy changes (that is, types that require reorg data).

/end example\]

## Root Cause

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\[/example: When two connections perform a lossy column type change at the same time (for example: modify column col char - > int), because the second column type change operation overrides the new column ID with the ID of the old column (before both DDL statements are executed), resulting in an inconsistent column type and data in the table structure. More detailed introduction: the solution to the problem of inconsistent table structure and data caused by concurrent column type changes in the same column ([https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#cvIyfR](https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#cvIyfR))

/end example\]

## Solution

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\[/example: The solution to the problem of inconsistent table structure and data caused by concurrent column type changes in the same column ([https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#cvIyfR](https://pingcap.feishu.cn/docs/doccnvSCiKf4hsACtZ7TiC2LQiY#cvIyfR))

/end example\]

## Impacted versions

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\* v5.1.0 - v5.1.3

\* v5.2.0 - v5.2.3

\* v5.3.0

## Mitigation/workaround

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\[/example: Disable parallel execution of the "alter table... modify/change column" statement on the same column of a table.

/end example\]

## Fix version (will be fixed in the following version)

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\[example:

\* v5.1.4

\* v5.2.4

\* v5.3.1

/end example\]

## Related Links

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\[example:

Add public links to any relevant supporting KB or TiDB documentation

/end example\]