EC
1656
MySQLERRORCommonReplicationHIGH confidence

Error writing to NDB exceptions table

Production Risk

High — conflicting rows are lost if the exceptions table cannot be written.

What this means

NDB conflict resolution attempted to write a rejected row to the exceptions table but failed, typically because the exceptions table is missing or has an incorrect schema.

Why it happens
  1. 1The NDB exceptions table does not exist.
  2. 2The exceptions table schema does not match the expected format.
  3. 3Disk space or permissions issue prevented the write.
How to reproduce
trigger — this will error
trigger — this will error
-- NDB conflict detected; exception row could not be written to mytable$EX

expected output

ERROR 1656 (HY000): Error writing to exceptions table.

Fix

Create the exceptions table with the correct schema

Create the exceptions table with the correct schema
-- Create exceptions table following NDB naming convention: <tablename>$EX

Why this works

A correctly structured exceptions table allows conflict rows to be logged.

Version notes

Sources
Official documentation ↗

MySQL 8.0 — 1656 ER_EXCEPTIONS_WRITE_ERROR

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