Bug #117717 Import Tablespace Fails Due to Inconsistent max_prefix in dict_col_t After Dropping Index

• Submitted: 16 Mar 2025 5:05
• Modified: 16 Mar 2025 11:35
• Reporter: Yichang Song (OCA)
• Status: Patch pending
• Category: MySQL Server: InnoDB storage engine
• Severity: S2 (Serious)
• Version: 8.0.41, 8.4.4, 9.2.0
• OS: Any
• CPU Architecture: Any

[16 Mar 2025 5:05] Yichang Song

Description:
When exporting/importing a tablespace using DISCARD/IMPORT TABLESPACE, the operation fails with ER_TABLE_SCHEMA_MISMATCH if:

1. The source table had an index with a prefix length that was the maximum prefix length for a column.
2. The index with the maximum prefix length was dropped before exporting.

The root cause is that dict_col_t::max_prefix (the maximum prefix length of a column across all indexes) is not updated when an index with the maximum prefix is dropped. This value is persisted in the .cfg file during FLUSH TABLES ... FOR EXPORT, causing a schema mismatch during import.

How to repeat:

create database src;
create database dst;

create table src.t1 (
  `name` varchar(128),
  KEY `name1` (`name`(8))
);
alter table src.t1 add index name2 (name(15));
alter table src.t1 drop index name2;
create table dst.t1 like src.t1;
alter table dst.t1 discard tablespace;
flush tables src.t1 for export;

--let $MYSQLD_DATADIR=`select @@datadir`
--copy_file $MYSQLD_DATADIR/src/t1.ibd $MYSQLD_DATADIR/dst/t1.ibd
--copy_file $MYSQLD_DATADIR/src/t1.cfg $MYSQLD_DATADIR/dst/t1.cfg

unlock tables;
# --error ER_TABLE_SCHEMA_MISMATCH
alter table dst.t1 import tablespace;

drop database src;
drop database dst;

Suggested fix:
Remove the validation of max_prefix during importing?

[16 Mar 2025 11:35] MySQL Verification Team

Hello Yichang Song,

Thank you for the report and feedback.

regards,
Umesh

[28 May 1:13] MySQL Admin

Posted by developer: Bug status updated to 'Patch pending'