Why Does MySQL Skip Redundant UPDATEs in ROW Binlog Mode?
This article tests whether MySQL re‑executes an UPDATE that sets a row to its existing values, comparing the behavior under binlog_format=ROW with binlog_row_image=FULL versus binlog_format=STATEMENT, and explains why redundant updates are ignored in ROW mode.
Background
This article tests whether MySQL re‑executes an UPDATE statement that does not change any data (i.e., the new values are identical to the existing ones).
Test Environment
MySQL 5.7.25
CentOS 7.4
binlog_format = ROW
1. Parameters
2. Test Steps
session1
session2
session1
3. Summary
When binlog_format=row and binlog_row_image=FULL , MySQL records all column values in the binlog, so reading the data pulls all fields. Consequently, an UPDATE that does not change any values is skipped: InnoDB receives a “modify to (1,55)” request, detects no change, and returns without updating.
binlog_format = STATEMENT
1. Parameters
2. Test Steps
session1
session2
session1
3. Summary
When binlog_format=statement and binlog_row_image=FULL , InnoDB fully executes the UPDATE, performing the “modify to (1,999)” operation, acquiring necessary locks and applying the change.
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