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Description

This error occurs when MySQL detects an `UPDATE IGNORE` statement that is considered unsafe for replication. The non-deterministic order in which rows are processed and potentially ignored can lead to data inconsistencies between the source and its replicas, making data integrity unreliable.

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Error Message

UPDATE IGNORE is unsafe because the order in which rows are updated determines which (if any) rows are ignored. This order cannot be predicted and may differ on source and the replica.

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Known Causes

3 known causes

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Using UPDATE IGNORE in Replication

The fundamental cause is employing `UPDATE IGNORE` in a MySQL environment configured for replication, where its inherent non-deterministic behavior risks data divergence.

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Non-Deterministic Row Processing Order

`UPDATE IGNORE` does not guarantee a specific order for processing rows, meaning which rows are ignored can vary unpredictably between the source and replicas, leading to inconsistent data.

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Statement-Based Replication Context

This issue is particularly problematic in statement-based replication (SBR) or when mixed-mode logging defaults to SBR for such statements, as the exact non-deterministic statement is replayed.

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Solutions

3 solutions available

1. Avoid UPDATE IGNORE with Primary Keys medium

The most robust solution is to ensure your UPDATE statements are not using IGNORE and instead handle potential duplicate key errors explicitly.

1

Identify the `UPDATE IGNORE` statements causing the replication error. These are usually found in your application code or in stored procedures/triggers.

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2

Modify the `UPDATE IGNORE` statements. Instead of IGNORE, use a standard `UPDATE` statement and handle potential duplicate key errors in your application logic. This might involve checking for the existence of a record before attempting to update, or using `INSERT ... ON DUPLICATE KEY UPDATE` if the intent is to insert or update.

UPDATE your_table SET column1 = 'value1' WHERE id = 1;
-- Instead of:
-- UPDATE IGNORE your_table SET column1 = 'value1' WHERE id = 1;

3

If the intention is to insert a new row or update an existing one if it already exists, use `INSERT ... ON DUPLICATE KEY UPDATE`. This is a safe and deterministic operation for replication.

INSERT INTO your_table (id, column1) VALUES (1, 'value1') ON DUPLICATE KEY UPDATE column1 = 'value1';

4

Deploy the modified application code or database objects to both the source and replica servers.

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2. Ensure Deterministic Ordering with a Unique Key medium

If you must use `UPDATE IGNORE`, ensure the `WHERE` clause uniquely identifies rows and that the column(s) used in the `WHERE` clause are part of a unique index or primary key.

1

Examine the `UPDATE IGNORE` statement and identify the columns used in the `WHERE` clause.

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2

Verify that the columns in the `WHERE` clause, when combined, form a unique key for the table. This can be a primary key or a unique index.

SHOW INDEX FROM your_table WHERE Non_unique = 0;

3

If the `WHERE` clause does not guarantee uniqueness, add a unique index to the table on the relevant columns. **Caution:** Adding indexes can impact write performance.

ALTER TABLE your_table ADD UNIQUE INDEX idx_unique_key (column_a, column_b);

4

Ensure this unique index exists on both the source and replica servers before executing the `UPDATE IGNORE` statement.

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3. Replicate with Global Transaction Identifiers (GTIDs) advanced

Using GTIDs can help mitigate some replication issues, including those related to statement ordering, by ensuring that transactions are applied in the same order on both source and replica.

1

Enable GTIDs on both your source and replica MySQL servers. This is a server-level configuration change.

In `my.cnf` or `my.ini`:
[mysqld]
gtid_mode = ON
enable_gtid_by_current_pos = ON

Then restart your MySQL server.

2

Re-configure your replication channel to use GTIDs. This typically involves stopping replication, resetting the slave, and then configuring it to use GTIDs.

STOP SLAVE;
RESET SLAVE ALL;
CHANGE MASTER TO MASTER_AUTO_POSITION = 1;
START SLAVE;

3

Monitor replication status to ensure it is healthy and that the `Unsafe UPDATE IGNORE Replication` error no longer occurs. While GTIDs improve transactional consistency, `UPDATE IGNORE` can still cause data divergence if the underlying data state differs significantly between source and replica.

SHOW SLAVE STATUS\G

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Related Errors

5 related errors

MySQL Error 1719: Unsafe UPDATE IGNORE Replication