Data lossy column type modification makes TiFlash data inconsistent

[Lloyd-Pottiger]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Create a table t
2. Insert data more than 100 MB
3. Add a column nullable col with default a
4. Do a lossy column type modification and change default value to null
5. Run update t set col = null where col = a
6. Run the following query, then we can find the result is inconsistent.

set @@tidb_isolation_read_engines='tiflash'; select count(*) from t where col = a;
set @@tidb_isolation_read_engines='tikv'; select count(*) from t where col = a;

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

master

[Dylan0222]

Hi, I’m curious about the reference to “more than 1 GiB”—does this imply that the bug can only be reproduced under large-scale scenarios? However, it appears the commit does not include any changes to the storage layer.