Release Notes for MariaDB Xpand 6.0.3

Columnar Indexes

• MariaDB Xpand 6 provides support for columnar indexes, which can be used to speed up performance of OLAP-style queries.

• Columnar indexes can improve performance of ad-hoc queries, where the fields in a query are not known in advance, because Columnar indexes provide efficient filtration capabilities that are not dependent on column order.

• Columnar indexes can improve performance of operational analytics, where real-time analytics are performed on transactional data, because Columnar indexes outperform row-based secondary indexes for analytical queries that perform range scans and aggregations.

• Columnar indexes are compressed automatically.

• A single Columnar index can be created for each table.

• Single column and composite (multi-column) Columnar indexes can be defined.

• To add a Columnar index to an existing table, execute ALTER TABLE .. ADD COLUMNAR INDEX:

ALTER TABLE hq_sales.invoices
   ADD COLUMNAR INDEX cols (invoice_date, invoice_total);

• For best performance, MariaDB recommends loading data into the table prior to adding a Columnar index.

• The cost_read_column system variable is used for costing columnar reads. The default value of cost_read_column in Xpand 5.3 was 0.01. For deployments upgrading to Xpand 6 from previous versions, the value of cost_read_column should be set to 0.9.

• For additional information, see "MariaDB Xpand Columnar Index Architecture".

Parallel Replication

• In MariaDB Xpand 6, parallel replication is Generally Available (GA) and suitable for production.

• Parallel replication minimizes latency and slave lag.

• Parallel replication provides extremely scalable replication. When parallel replication is configured to use a specified number of parallel Slave Event Readers / Applicators, Xpand uses the consistent hashing algorithm to uniformly distribute the Slave Event Readers / Applicators between all of the nodes. The Slave Event Readers / Applicators on each node independently perform work in parallel. Each Slave Event Reader / Applicator independently streams and applies binary log events in parallel, which allows the full power of the cluster to be used without any choke points.

• When parallel replication is used, MariaDB Xpand ensures transactional consistency and commits transactions in the same order as the replication primary.

• Parallel replication requires row-based replication (RBR).

• To configure parallel replication, execute CREATE SLAVE and set the options for parallel replication:

CREATE SLAVE slave_name PARALLEL_LOG = master_log_name, PARALLEL_POS = position, SLICES = num_slices, BATCH_SIZE_MS = batch_size
   [, MASTER_HOST = master_host]
   [, MASTER_USER = master_user]
   [, MASTER_PASSWORD =  master_password]
   [, MASTER_PORT = master_port];

• For additional information, see "MariaDB Xpand Parallel Replication Architecture".

Strict Mode

• MariaDB Xpand 6 includes some improvements related to strict mode.

• When sql_mode=STRICT_TRANS_TABLES is set, MariaDB Xpand 6 validates when values are out of range and performs type checks on input. Errors will be raised for invalid input for all data types except:

  • SET

  • UNSIGNED INT

  • BIT

  • ENUM

  • DATE

  • TIME

  • DATETIME

  • TIMESTAMP

  • YEAR

• For compatibility, MariaDB Xpand 6 adds dummy support for MariaDB Server's innodb_strict_mode system variable.

Exclude Statements from Binlogs

• MariaDB Xpand 6 provides a new system variable to exclude statements in the current session from being written to specific binlogs. (XPT-117)

• The sql_log_skip_binlogs system variable can be set at the session-level and accepts a comma-separated list of binlog names.

• To exclude the current session's statements from binlogA and binlogB, set the system variable by executing SET:

SET sql_log_skip_binlogs='binlogA,binlogB';

• To re-enable writes to all binlogs for the current session, set the system variable back to DEFAULT:

SET sql_log_skip_binlogs=DEFAULT;

Static PDs (Probability Distributions)

• MariaDB Xpand 6 provides the ability to statically collect PDs (Probability Distributions).

• Probability Distributions (PDs) are statistics on data distribution used to generate optimal query execution plans.

• Prior to this release, all Probability Distributions were dynamic.

• With this release, Static PDs allow statistics to be gathered on-demand, removing the overhead of continual statistics collection. With Static PDs, statistics can be collected off-peak and persisted indefinitely.

Xpand Branding

• MariaDB Xpand 6 includes some branding-related changes to directory names, file names, and messages.

• As part of re-branding efforts, some Clustrix-related files and directories have been changed to reference Xpand:

  • Renamed /etc/clustrix to /etc/xpand

  • Renamed /etc/clustrix/clxnode.conf to /etc/xpand/xpdnode.conf

  • Renamed uninstall_clustrix to uninstall_xpand

• Xpand's Alerter looks for noalerts in /etc/xpand.

• Xpand's Upgrader uses /etc/xpand instead of /etc/clustrix.

  • If /etc/xpand doesn't exist, the upgrader will print instructions on how to create a symbolic link to from /etc/clustrix to /etc/xpand, and the upgrade will be aborted.

  • Once a symbolic link exists, the upgrade can be re-run.

• Upgrade messages reference Xpand instead of Clustrix.

Other

• A command line argument has been added to specify the node's hostname. (XPT-44)

• rsync has been added to the list of RPM dependencies.

• The fielddebug and wal_fs_dump utilities are part of the standard Xpand rpm.

• Support for _utf8mb3 character set literals has been added.

• OOM protection applies only when Xpand runs as root.

• clx_import will not re-slice ALLNODES tables.

• clx_import can prompt for password:

  • Prior to this release, clx_import required password to be specified on the command-line.

  • With this release, clx_import prompts for password when not specified on the command-line. (XPT-68)

• When sierra_allow_right_deep_tree=1 is set, query plans are improved.

• When a query contains a LEFT JOIN with an IN(..) list predicate, cardinality estimates are improved.

• The softfail procedure has been updated to include additional steps when binlogs are present. (XPT-256)

Can result in data loss

• After a partial rollback, corruption could occur when writing undo log records due to an issue with cache validation.

Can result in a hang or crash

• When STOP SLAVE is executed, the slave node could crash.

• When parallel replication is configured, an Xpand node could crash due to an out of memory condition. (XPT-135)

• During query optimization, internal statistics could be erroneously re-used and cause a crash.

• When multiple sessions concurrently execute ANALYZE TABLE on the same table, a crash could occur.

Can result in unexpected behavior

• When the binlog indexer is behind, the performance of SHOW BINLOG FILES could be impacted. (XPT-113)

• When the binlog indexer encounters a 0-size transaction, the binlog indexer could not proceed, and performance of SHOW BINLOG FILES and TRIM BINLOG could be impacted. (XPT-164)

• Logging for an RBR replication slave does not correctly surface information about errors. (XPT-255)

• REPAIR TABLE does not work with generated columns.

• When a query containing an IN(..) list is executed as a prepared statement, the prepared statement could be translated multiple times.

• Upgrades could re-set variables that were aliased, such as mysql_port and port. (XPT-162)

• A group change could result in a container being leaked. (XPT-98)

• Replication to or from MariaDB Server 10.6 does not work.

• When a user tries to change their own password with SET PASSWORD, the SUPER privilege is incorrectly required. (XPT-148)

• Logging should occur earlier in the group change process to optimize group change performance for environments where the HugeTLB is not enabled. (XPT-183)

• When sql_mode=STRICT_TRANS_TABLES is set, a negative value inserted into an UNSIGNED FLOAT does not raise an error. (XPT-143)

• When sql_mode=STRICT_TRANS_TABLES is set, validation is not performed for FLOAT, DOUBLE, and REAL UNSIGNED. (XPT-143)

• Arguments to the current_timestamp(), current_time(), curtime(), now(), localtime(), localtimestamp(), utc_timestamp(), and utc_time() functions are not required to be in a valid range.

• uninstall_clustrix is not replaced with uninstall_xpand when upgrading from previous Xpand versions.

• Additional clx options could not be used in conjunction with debugdump.

• The CLX tool can not parse Unicode characters.

• Changes to MAX_REDO in clxnode.conf are not applied.

• Executing SHOW COLUMNS or SHOW FIELDS executed against a non-existent table does not throw an error.

• The USE INDEX hint does not work with DELETE statements.

Added System Variables

Changed System Variable Defaults

Renamed Files and Directories

• Renamed /etc/clustrix to /etc/xpand

• Renamed /etc/clustrix/clxnode.conf to /etc/xpand/xpdnode.conf

• Renamed uninstall_clustrix to uninstall_xpand

Changes to statd and exporters

• Added stats to statd and exporters for:

  • lockman.sessions_holding_locks

  • lockman.waiters histogram

  • sessions.node.X.limit and sessions.node.X.remaining

  • transactions.open.seconds

  • io.network.internode.latency.seconds

• Renamed statd metric from lockman.num_locks to lockman.num_waiters (XPT-165)