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TwinCommitDocs

MySQL

TwinCommit captures changes from MySQL by reading the binary log as a replica would. It uses row-based events with full row images and GTIDs, buffers changes per transaction and applies each committed transaction in commit order. Nothing is installed in the database.

Supported: MySQL 8.0, 8.4 LTS and 9.x · Amazon RDS for MySQL · Aurora MySQL · Azure Database for MySQL Flexible Server · Google Cloud SQL for MySQL.

Prerequisites

Section titled “Prerequisites”

Binary log settings

Section titled “Binary log settings”
# my.cnf
[mysqld]
server_id               = 101
log_bin                 = mysql-bin
binlog_format           = ROW
binlog_row_image        = FULL
gtid_mode               = ON
enforce_gtid_consistency = ON
binlog_expire_logs_seconds = 604800   # keep 7 days so a stopped pipeline can resume

On RDS and Aurora, set these through a parameter group and keep binlogs available with:

CALL mysql.rds_set_configuration('binlog retention hours', 168);

User

Section titled “User”
CREATE USER 'twincommit'@'%' IDENTIFIED BY '********';
GRANT REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'twincommit'@'%';
GRANT SELECT ON app.* TO 'twincommit'@'%';   -- for snapshots

Primary keys

Section titled “Primary keys”

Every replicated table needs a primary key or a non-null unique key.

Configuration

Section titled “Configuration”
source:
  type: mysql
  host: mysql-primary.internal
  port: 3306
  user: twincommit
  password: ${MYSQL_PASSWORD}
  server_id: 4201        # unique among all replicas of this server

Run twincommit check to confirm every setting. It prints the exact statement for anything that is missing.

How capture works

Section titled “How capture works”
  • TwinCommit registers as a replica with its own server_id and streams binlog events from the GTID recorded in its checkpoint.
  • Row events are grouped by transaction and released at XID (commit). Rolled-back transactions never appear in the binlog, so nothing partial reaches the target.
  • The snapshot runs in a consistent-read transaction and records the GTID set at its start, so streaming resumes exactly where the snapshot ends. See snapshots.

Limitations

Section titled “Limitations”
  • binlog_format = STATEMENT or MIXED is not supported.
  • binlog_row_image = MINIMAL or NOBLOB is not supported; TwinCommit needs full before and after images.
  • Tables using the MEMORY or BLACKHOLE engines are not captured.
  • DDL is detected, not propagated. See schema changes.