# Galera Cluster System Tables Starting with Galera 4 (used in [MariaDB 10.4](https://app.gitbook.com/s/aEnK0ZXmUbJzqQrTjFyb/community-server/old-releases/10.4/what-is-mariadb-104) and later), several system tables related to replication are available in the `mysql` database. These tables can be queried by administrators to get a real-time view of the cluster's layout, membership, and current operations. You can view these tables with the following query: ```sql SHOW TABLES FROM mysql LIKE 'wsrep%'; ``` ``` +---------------------------+ | Tables_in_mysql (wsrep%) | +---------------------------+ | wsrep_allowlist | | wsrep_cluster | | wsrep_cluster_members | | wsrep_streaming_log | +---------------------------+ ``` {% hint style="warning" %} `mysql` vs. `mariadb` You'll see queries referencing the `mysql` database (e.g., `FROM mysql.wsrep_cluster`). This is intentional. MariaDB, a MySQL fork, retains the `mysql` name for its internal system schema to ensure historical and backward compatibility where it manages user permissions and system tables. This is different from the command-line client, which should always be invoked as `mariadb`. {% endhint %} These tables are managed by the cluster itself and should not be modified by users, with the exception of `wsrep_allowlist`. ## `wsrep_allowlist` This table stores a list of allowed IP addresses that can join the cluster and perform a state transfer (IST/SST). It is a security feature to prevent unauthorized nodes from joining. ```bash MariaDB [mysql]> DESCRIBE wsrep_allowlist; ``` ``` +-------+----------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+----------+------+-----+---------+-------+ | ip | char(64) | NO | PRI | NULL | | +-------+----------+------+-----+---------+-------+ ``` To add a new node to the allowlist, you can `INSERT` its IP address: ```sql INSERT INTO mysql.wsrep_allowlist(ip) VALUES('18.193.102.155'); ``` If a node attempts to join and its IP address is not in the allowlist, the join will fail. The DONOR nodes will log a warning similar to this: ``` [Warning] WSREP: Connection not allowed, IP 3.70.155.51 not found in allowlist. ``` The joining node will fail with a connection timeout error. ## `wsrep_cluster` This table contains a single row with a high-level view of the cluster's identity, state, and capabilities. | Attribute | Description | | ------------------ | -------------------------------------------------------------------------------------------------------- | | `cluster_uuid` | The unique identifier for the cluster. | | `view_id` | Corresponds to the `wsrep_cluster_conf_id` status variable, representing the current membership view ID. | | `view_seqno` | The global transaction sequence number associated with this cluster view. | | `protocol_version` | The wsrep protocol version in use. | | `capabilities` | A bitmask of capabilities provided by the Galera library. | You can query its contents like this: ```sql SELECT * FROM mysql.wsrep_cluster\G ``` ``` *************************** 1. row *************************** cluster_uuid: bd5fe1c3-7d80-11e9-8913-4f209d688a15 view_id: 3 view_seqno: 2956 protocol_version: 4 capabilities: 184703 ``` ## `wsrep_cluster_members` This table provides a real-time list of all the nodes that are currently members of the cluster component. | Node | Description | | ----------------------- | ---------------------------------------------------------------------------- | | `node_uuid` | The unique identifier for each individual node. | | `cluster_uuid` | The UUID of the cluster this node belongs to. | | `node_name` | The human-readable name of the node, set by the `wsrep_node_name` parameter. | | `node_incoming_address` | The IP address and port where the node is listening for client connections. | Querying this table gives you a quick overview of the current cluster membership: ```sql SELECT * FROM mysql.wsrep_cluster_members ORDER BY node_name\G ``` ``` *************************** 1. row *************************** node_uuid: e39d1774-7e2b-11e9-b5b2-7696f81d30fb cluster_uuid: bd5fe1c3-7d80-11e9-8913-4f209d688a15 node_name: galera1 node_incoming_address: AUTO *************************** 2. row *************************** node_uuid: eb8fc512-7e2b-11e9-bb74-3281cf207f60 cluster_uuid: bd5fe1c3-7d80-11e9-8913-4f209d688a15 node_name: galera2 node_incoming_address: AUTO *************************** 3. row *************************** node_uuid: 2347a8ac-7e2c-11e9-b6f0-da90a2d0a563 cluster_uuid: bd5fe1c3-7d80-11e9-8913-4f209d688a15 node_name: galera3 node_incoming_address: AUTO ``` ## `wsrep_streaming_log` This table contains metadata for Streaming Replication transactions that are currently in progress. Each row represents a write-set fragment. The table is typically empty unless a large or long-running transaction with streaming enabled is active. | Fragment | Description | | ----------- | ---------------------------------------------------------------- | | `node_uuid` | The UUID of the node where the streaming transaction originated. | | `trx_id` | The transaction identifier. | | `seqno` | The sequence number of the specific write-set fragment. | | `flags` | Flags associated with the fragment. | | `frag` | The binary log events contained in the fragment. | Example of querying the table during a streaming transaction: ```sql -- Enable streaming for the session SET SESSION wsrep_trx_fragment_unit='statements'; SET SESSION wsrep_trx_fragment_size=1; ``` ```sql -- Start a transaction START TRANSACTION; INSERT INTO my_table VALUES (100); ``` ```sql -- Query the log table in the same session SELECT node_uuid, trx_id, seqno, flags FROM mysql.wsrep_streaming_log; ``` ``` +--------------------------------------+--------+-------+-------+ | node_uuid | trx_id | seqno | flags | +--------------------------------------+--------+-------+-------+ | a006244a-7ed8-11e9-bf00-867215999c7c | 26 | 4 | 1 | +--------------------------------------+--------+-------+-------+ ``` *This page is licensed: CC BY-SA / Gnu FDL*