4084
MySQLERRORCommonHIGH confidence
InnoDB online index rebuild failed
Production Risk
High — Failed index rebuild leaves the table without the intended index and may cause query plan regressions.
Why it happens
- 1Insufficient temporary disk space for the sort buffer during index rebuild.
- 2A lock timeout or deadlock interrupted the online DDL operation.
- 3The table contains corrupted rows that prevent index creation.
Fix 1
Increase innodb_sort_buffer_size
Increase innodb_sort_buffer_size
SET GLOBAL innodb_sort_buffer_size = 67108864;
Why this works
Provides more memory for sorting rows during the index build phase.
Fix 2
Retry with ALGORITHM=COPY if online fails
Retry with ALGORITHM=COPY if online fails
ALTER TABLE t ADD INDEX idx (col) ALGORITHM=COPY;
Why this works
Falls back to a table copy which avoids online rebuild constraints.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 4084 ER_INNODB_INDEX_ONLINE_REBUILD_FAILED
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