Re: Table Problems on legacy databases

[Simon raphael]

This appears to be a classic InnoDB dictionary mismatch from a 5.7 to 8.4 upgrade. MySQL 8 has a new data dictionary; copying .frm/.ibd folders over won’t work and gives a “table doesn’t exist” error, even when the files are present.

Recovery path (works reliably):

Spin up a separate MySQL 5.7 VM (same build if possible). Copy the entire datadir (including ibdata1, ib_logfile*, and not just the database folders).

Start with innodb_force_recovery=1 and raise to 4–6 only if needed (read-only).

Dump everything with mysqldump --single-transaction --routines --triggers --events --skip-lock-tables.

For tables still failing (1146), but you have .frm + .ibd:

Recreate structure from the .frm (use mysqlfrm or Percona’s tools),

ALTER TABLE … DISCARD TABLESPACE; copy the .ibd,

ALTER TABLE … IMPORT TABLESPACE;

Restore the dumps into a clean MySQL 8.4 instance.

Also check:

Lower-case table names must match between the old and new servers.

Don’t REPAIR on InnoDB.

If you only have a .frm file (without a .ibd file and the table is not in ibdata1), the data is likely lost.

This approach usually gets the “bad half” back long enough to dump cleanly before upgrading.