Configuring permissions for Alibaba Canal involves standard replication grants, specifically REPLICATION SLAVE and REPLICATION CLIENT. However, the requirement for the SELECT privilege often leads to confusion regarding its necessary scope—whether it must be applied at the database level or if table-level access suffices.

Initial testing in local development environments might produce misleading results. In many standalone instances, revoking global SELECT permissions does not immediately disrupt the binlog synchronization process. This anomaly occurs because the parser might not need to fetch new metadata if the table structure is already cached or if the specific query type does not trigger a metadata check.

However, behavior changes in high-availability clusters, such as those managed by MHA. When the SELECT privilege is removed from the target database in these environments, the Canal instance throws a parsing exception. The log typically indicates a failure to fetch table metadata, often accompanied by an IOError stating SELECT command denied for a specific table.

This failure stems from the TableMetaCache logic. To correctly parse row events and convert binary logs into structured data, Canal must understand the table schema. It executes commands like DESCRIBE tableName or SHOW CREATE TABLE to retrieve column definitions. Without SELECT access, the database denies these metadata queries, causing the parser to crash. Consequently, granting SELECT privileges is mandatory for the specific databases or tables being synchronized to ensure the parser can resolve table structures. The discrepancy between local and cluster behavior may be influenced by configuration parameters like master_info_repository, which affects how replication state is managed.

The following SQL commands demonstrate the correct approach to managing these permissions:

-- Granting necessary privileges
GRANT SELECT, REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'canal_user'@'%';
FLUSH PRIVILEGES;

-- Verifying current grants
SHOW GRANTS FOR 'canal_user'@'%';

-- Revoking global SELECT if granular control is needed (ensure table-level grants exist first)
REVOKE SELECT ON *.* FROM 'canal_user'@'%';
FLUSH PRIVILEGES;