system Tables in Xpand
This page is part of MariaDB's MariaDB Documentation.
The parent of this page is: Reference for MariaDB Xpand
Topics on this page:
MariaDB Xpand includes system tables in the
Rough estimate of progress for an
Per-session statistics on transaction and statement types.
Databases containing Xpand tables.
Stores information on open transactions.
Histograms of node to node network latencies.
Information on each Replica Server that is currently connected to the Xpand service.
Information related to replication when Xpand is configured for in-bound replication
Provides a list of partitions and their sizes.
Details on operations performed by the rebalancer process and the reason why the operation was triggered.
Summary of current rebalancer operations.
Details on Xpand tables in the deployment.
Details on representations produced by each index on each Xpand table. These are the basis for data distribution through the Xpand deployment.
Stores the names of all roles on the Xpand cluster.
Stores the mapping between roles and and user specifications, including whether the user was granted
Stores the list of roles available to a session.
Information on currently connection and recently disconnected sessions.
Internal statistics on database and deployment performance.
Information on database users, host, and password combinations.
Contains one row for each replica in the system and records each replica's size and node.
Total size of each Xpand table.
Information on table slices, produced by dividing representations of each Xpand table.
Stores database user, host, and password combinations.
Stores a mapping between roles and user specifications, including whether the role is a default role for the user.
Stores a histogram that tracks disk latency.
History of installation and upgrade versions.
alter_progress table provides a rough estimate of the progress for an
The ID for the session.
The name of the source relation.
Timestamp for when the alter started.
The number of rows read by the
The estimated number of rows in the source relation
A rough estimate of when the
cluster_session_stats table contains per-session statistics about transactions and statement types.
databases table contains one row for each database in the system. Its columns are as follows:
Contains an ID for each database. It corresponds to the
Contains the ID of the user who created the database. It corresponds to the
Name of the database.
Indicates whether the table is hidden from users when performing queries:
An internal value that encodes the character set and collation sequence utilized by a given database.
To translate this encoded value to English, a special function is available as follows:
SELECT OIDTYPE_CSCL_PROP(cscl, 'charset') FROM system.databases WHERE name = 'sample'; SELECT OIDTYPE_CSCL_PROP(cscl, 'collation') FROM system.databases WHERE name = 'sample';
gtm_coord table contains a row for each open transaction.
internode_latency_histogram table stores histograms of node to node network latencies.
mysql_master_status table stores information about each replication slave that is currently connected to the cluster.
mysql_slave_stats table contains information related to replication when Xpand is configured for in-bound replication
partition_sizes table provides a list of partitions and their sizes.
rebalancer_activity_log table contains a detailed log of Rebalancer actions and the reasons for those actions. For additional information, see "Manage the Rebalancer for MariaDB Xpand".
The cluster performs ongoing optimization tasks in background mode. In rare cases, this background activity might affect query performance. In such cases, the Rebalancer, which moves data between disks and nodes to ensure even distribution, is a likely source. Rebalancing typically runs after an import, and occasionally runs as disk utilization increases. Because Rebalancer sessions can be brief, the
rebalancer_activity_log table is a better source for detailed information.
Values returned in the
action column are as follows:
A slice has grown too large and is being split into two smaller slices.
A slice is being moved to another disk or node to optimize the load.
A slice is being duplicated, usually during the reprotection stage after a hardware failure.
relations table contains one row for each table in the system.
representations table contains one row per representation in the system. Each relation and each index on that relation constitutes a representation. The
base column indicates when the representation is the Base Representation.
roles table contains the names of all roles on the Xpand cluster.
roles_mapping table contains the mapping between roles and and user specifications, including whether the user was granted
WITH ADMIN for the role.
session_roles table contains the list of roles available to a session.
sessions table contains information about all currently connected and recently disconnected client sessions.
stats table contains internally-collected statistics about database and cluster performance. Most of these statistics are for internal use, but some are of general interest.
system_users table contains information on database users, host, and password combinations.
table_replicas table contains one row for each replica in the system and records each replica's size and node. This table can be used to determine the total calculated size of an index and to find poorly-distributed indexes. each slice is replicated two or more times and each replica resides on a different node. Each replica of a slice contains the same data.
table_sizes table records the total size of each table in bytes, including its base representation and all of its indexes.
Representations are split into slices and distributed throughout your cluster. The
table_slices table enumerates those slices and indexes and contains one row for each slice in each table.
Each slice contains a unique set of rows from the table. The complete table is represented by assembling all the rows from the table slices. The rows are allocated to slices using a hash that is based on the row's index or indices. The number of slices per table depends on many factors including the size of the cluster. To configure this setting, issue the
ALTER TABLE SET SLICES = <N> command. Changing the slice count can improve performance. For details, contact MariaDB support.
To display the names of the database, table, and indexes for each slice, join on the
users table contains database user, host, and password combinations. Join to this table to display user names instead of user ids. For additional information, see "Database User Accounts for MariaDB Xpand".
user_role_links table stores a mapping between roles and user specifications, including whether the role is a default role for the user.
IO_ LATENCY_ HISTOGRAM
vdev_io_latency_histogram table stores a histogram that tracks disk latency.
version_history table provides a history of installation and upgrade versions.