MySQL connector

The MySQL connector allows querying and creating tables in an external MySQL instance. This can be used to join data between different systems like MySQL and Hive, or between two different MySQL instances.

Requirements

To connect to MySQL, you need:

• MySQL 5.7, 8.0 or higher.
• Network access from the Trino coordinator and workers to MySQL. Port 3306 is the default port.

Configuration

To configure the MySQL connector, create a catalog properties file in etc/catalog named, for example, mysql.properties, to mount the MySQL connector as the mysql catalog. Create the file with the following contents, replacing the connection properties as appropriate for your setup:

connector.name=mysql
connection-url=jdbc:mysql://example.net:3306
connection-user=root
connection-password=secret

The connection-url defines the connection information and parameters to pass to the MySQL JDBC driver. The supported parameters for the URL are available in the MySQL Developer Guide.

For example, the following connection-url allows you to configure the JDBC driver to interpret time values based on UTC as a timezone on the server, and serves as a workaround for a known issue.

connection-url=jdbc:mysql://example.net:3306?serverTimezone=UTC

The connection-user and connection-password are typically required and determine the user credentials for the connection, often a service user. You can use secrets to avoid actual values in the catalog properties files.

Connection security

If you have TLS configured with a globally-trusted certificate installed on your data source, you can enable TLS between your cluster and the data source by appending a parameter to the JDBC connection string set in the connection-url catalog configuration property.

For example, with version 8.0 of MySQL Connector/J, use the sslMode parameter to secure the connection with TLS. By default the parameter is set to PREFERRED which secures the connection if enabled by the server. You can also set this parameter to REQUIRED which causes the connection to fail if TLS is not established.

You can set the sslMode paremeter in the catalog configuration file by appending it to the connection-url configuration property:

connection-url=jdbc:mysql://example.net:3306/?sslMode=REQUIRED

For more information on TLS configuration options, see the MySQL JDBC security documentation.

Multiple MySQL servers

You can have as many catalogs as you need, so if you have additional MySQL servers, simply add another properties file to etc/catalog with a different name, making sure it ends in .properties. For example, if you name the property file sales.properties, Trino creates a catalog named sales using the configured connector.

General configuration properties

The following table describes general catalog configuration properties for the connector:

Property name	Description	Default value
case-insensitive-name-matching	Support case insensitive schema and table names.	false
case-insensitive-name-matching.cache-ttl		1m
case-insensitive-name-matching.config-file	Path to a name mapping configuration file in JSON format that allows Trino to disambiguate between schemas and tables with similar names in different cases.	null
case-insensitive-name-matching.refresh-period	Frequency with which Trino checks the name matching configuration file for changes.	0 (refresh disabled)
metadata.cache-ttl	Duration for which metadata, including table and column statistics, is cached.	0 (caching disabled)
metadata.cache-missing	Cache the fact that metadata, including table and column statistics, is not available	false
metadata.cache-maximum-size	Maximum number of objects stored in the metadata cache	10000
write.batch-size	Maximum number of statements in a batched execution. Do not change this setting from the default. Non-default values may negatively impact performance.	1000

Procedures

• system.flush_metadata_cache()

  Flush JDBC metadata caches. For example, the following system call flushes the metadata caches for all schemas in the example catalog

  USE example.myschema;
  CALL system.flush_metadata_cache();

Case insensitive matching

When case-insensitive-name-matching is set to true, Trino is able to query non-lowercase schemas and tables by maintaining a mapping of the lowercase name to the actual name in the remote system. However, if two schemas and/or tables have names that differ only in case (such as "customers" and "Customers") then Trino fails to query them due to ambiguity.

In these cases, use the case-insensitive-name-matching.config-file catalog configuration property to specify a configuration file that maps these remote schemas/tables to their respective Trino schemas/tables:

{
  "schemas": [
    {
      "remoteSchema": "CaseSensitiveName",
      "mapping": "case_insensitive_1"
    },
    {
      "remoteSchema": "cASEsENSITIVEnAME",
      "mapping": "case_insensitive_2"
    }],
  "tables": [
    {
      "remoteSchema": "CaseSensitiveName",
      "remoteTable": "tablex",
      "mapping": "table_1"
    },
    {
      "remoteSchema": "CaseSensitiveName",
      "remoteTable": "TABLEX",
      "mapping": "table_2"
    }]
}

Queries against one of the tables or schemes defined in the mapping attributes are run against the corresponding remote entity. For example, a query against tables in the case_insensitive_1 schema is forwarded to the CaseSensitiveName schema and a query against case_insensitive_2 is forwarded to the cASEsENSITIVEnAME schema.

At the table mapping level, a query on case_insensitive_1.table_1 as configured above is forwarded to CaseSensitiveName.tablex, and a query on case_insensitive_1.table_2 is forwarded to CaseSensitiveName.TABLEX.

By default, when a change is made to the mapping configuration file, Trino must be restarted to load the changes. Optionally, you can set the case-insensitive-name-mapping.refresh-period to have Trino refresh the properties without requiring a restart:

case-insensitive-name-mapping.refresh-period=30s

Non-transactional INSERT

The connector supports adding rows using INSERT statements </sql/insert>. By default, data insertion is performed by writing data to a temporary table. You can skip this step to improve performance and write directly to the target table. Set the insert.non-transactional-insert.enabled catalog property or the corresponding non_transactional_insert catalog session property to true.

Note that with this property enabled, data can be corrupted in rare cases where exceptions occur during the insert operation. With transactions disabled, no rollback can be performed.

Type mapping

Because Trino and MySQL each support types that the other does not, this connector modifies some types when reading or writing data.

MySQL to Trino read type mapping

This connector supports reading the following MySQL types and performs conversion to Trino types with the detailed mappings as shown in the following table.

MySQL to Trino type mapping

MySQL database type	Trino type	Notes
BIT	BOOLEAN
BOOLEAN	TINYINT
TINYINT	TINYINT
SMALLINT	SMALLINT
INTEGER	INTEGER
BIGINT	BIGINT
DOUBLE PRECISION	DOUBLE
FLOAT	REAL
REAL	REAL
DECIMAL(p, s)	DECIMAL(p, s)	See MySQL DECIMAL type handling
CHAR(n)	CHAR(n)
VARCHAR(n)	VARCHAR(n)
TINYTEXT	VARCHAR(255)
TEXT	VARCHAR(65535)
MEDIUMTEXT	VARCHAR(16777215)
LONGTEXT	VARCHAR
BINARY, VARBINARY, TINYBLOB,BLOB, MEDIUMBLOB, LONGBLOB	VARBINARY
DATE	DATE
TIME(n)	TIME(n)
DATETIME(n)	DATETIME(n)
TIMESTAMP(n)	TIMESTAMP(n)

No other types are supported.

Trino to MySQL write type mapping

This connector supports writing the following Trino types and performs conversion to MySQL types with the detailed mappings as shown in the following table.

Trino to MySQL type mapping

Trino type	MySQL type	Notes
BOOLEAN	TINYINT
TINYINT	TINYINT
SMALLINT	SMALLINT
INTEGER	INTEGER
BIGINT	BIGINT
REAL	REAL
DOUBLE	DOUBLE PRECISION
DECIMAL(p, s)	DECIMAL(p, s)	MySQL DECIMAL type handling
CHAR(n)	CHAR(n)
VARCHAR(n)	VARCHAR(n)
DATE	DATE
TIME(n)	TIME(n)
TIMESTAMP(n)	TIMESTAMP(n)

No other types are supported.

Decimal type handling

DECIMAL types with precision larger than 38 can be mapped to a Trino DECIMAL by setting the decimal-mapping configuration property or the decimal_mapping session property to allow_overflow. The scale of the resulting type is controlled via the decimal-default-scale configuration property or the decimal-rounding-mode session property. The precision is always 38.

By default, values that require rounding or truncation to fit will cause a failure at runtime. This behavior is controlled via the decimal-rounding-mode configuration property or the decimal_rounding_mode session property, which can be set to UNNECESSARY (the default), UP, DOWN, CEILING, FLOOR, HALF_UP, HALF_DOWN, or HALF_EVEN (see RoundingMode).

Type mapping configuration properties

The following properties can be used to configure how data types from the connected data source are mapped to Trino data types and how the metadata is cached in Trino.

Property name	Description	Default value
unsupported-type-handling	Configure how unsupported column data types are handled: IGNORE, column is not accessible. CONVERT_TO_VARCHAR, column is converted to unboundedVARCHAR. The respective catalog session property isunsupported_type_handling.	IGNORE
jdbc-types-mapped-to-varchar	Allow forced mapping of comma separated lists of data types to convert to unbounded VARCHAR

Querying MySQL

The MySQL connector provides a schema for every MySQL database. You can see the available MySQL databases by running SHOW SCHEMAS:

SHOW SCHEMAS FROM mysql;

If you have a MySQL database named web, you can view the tables in this database by running SHOW TABLES:

SHOW TABLES FROM mysql.web;

You can see a list of the columns in the clicks table in the web database using either of the following:

DESCRIBE mysql.web.clicks;
SHOW COLUMNS FROM mysql.web.clicks;

Finally, you can access the clicks table in the web database:

SELECT * FROM mysql.web.clicks;

If you used a different name for your catalog properties file, use that catalog name instead of mysql in the above examples.

SQL support

The connector provides read access and write access to data and metadata in the MySQL database. In addition to the globally available and read operation statements, the connector supports the following statements:

• INSERT
• DELETE
• TRUNCATE
• CREATE TABLE
• CREATE TABLE
• DROP TABLE
• CREATE SCHEMA
• DROP SCHEMA

SQL DELETE

If a WHERE clause is specified, the DELETE operation only works if the predicate in the clause can be fully pushed down to the data source.

Performance

The connector includes a number of performance improvements, detailed in the following sections.

Table statistics

The MySQL connector can use table and column statistics for cost based optimizations, to improve query processing performance based on the actual data in the data source.

The statistics are collected by MySQL and retrieved by the connector.

The table-level statistics are based on MySQL's INFORMATION_SCHEMA.TABLES table. The column-level statistics are based on MySQL's index statistics INFORMATION_SCHEMA.STATISTICS table. The connector can return column-level statistics only when the column is the first column in some index.

MySQL database can automatically update its table and index statistics. In some cases, you may want to force statistics update, for example after creating new index, or after changing data in the table. You can do that by executing the following statement in MySQL Database.

ANALYZE TABLE table_name;

note

MySQL and Trino may use statistics information in different ways. For this reason, the accuracy of table and column statistics returned by the MySQL connector might be lower than than that of others connectors.

Improving statistics accuracy

You can improve statistics accuracy with histogram statistics (available since MySQL 8.0). To create histogram statistics execute the following statement in MySQL Database.

ANALYZE TABLE table_name UPDATE HISTOGRAM ON column_name1, column_name2, ...;

Refer to MySQL documentation for information about options, limitations and additional considerations.

Pushdown

The connector supports pushdown for a number of operations:

• Pushdown
• Pushdown
• Pushdown

Aggregate pushdown for the following functions:

• avg
• count
• max
• min
• sum
• stddev
• stddev_pop
• stddev_samp
• variance
• var_pop
• var_samp

Cost-based join pushdown

The connector supports cost-based join-pushdown to make intelligent decisions about whether to push down a join operation to the data source.

When cost-based join pushdown is enabled, the connector only pushes down join operations if the available /optimizer/statistics suggest that doing so improves performance. Note that if no table statistics are available, join operation pushdown does not occur to avoid a potential decrease in query performance.

The following table describes catalog configuration properties for join pushdown:

Property name	Description	Default value
join-pushdown.enabled	Enable join pushdown <join-pushdown>. Equivalent catalog session property <session-properties-definition> isjoin_pushdown_enabled.	true
join-pushdown.strategy	Strategy used to evaluate whether join operations are pushed down. Set to AUTOMATIC to enable cost-based join pushdown, orEAGER to push down joins whenever possible. Note thatEAGER can push down joins even when table statistics are unavailable, which may result in degraded query performance. Because of this, EAGER is only recommended for testing and troubleshooting purposes.	AUTOMATIC

Predicate pushdown support

The connector does not support pushdown of any predicates on columns with textual types <string-data-types> like CHAR or VARCHAR. This ensures correctness of results since the data source may compare strings case-insensitively.

In the following example, the predicate is not pushed down for either query since name is a column of type VARCHAR:

SELECT * FROM nation WHERE name > 'CANADA';
SELECT * FROM nation WHERE name = 'CANADA';