MariaDB коннектор#

Примечание

Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.

The MariaDB connector allows querying and creating tables in an external MariaDB database.

Requirements#

To connect to MariaDB, you need:

MariaDB version 10.2 or higher.
Network access from the Trino coordinator and workers to MariaDB. Port 3306 is the default port.

Конфигурация#

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

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

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.

Data source authentication#

The connector can provide credentials for the data source connection in multiple ways:

inline, in the connector configuration file
in a separate properties file
in a key store file
as extra credentials set when connecting to Trino

You can use secrets to avoid storing sensitive values in the catalog properties files.

The following table describes configuration properties for connection credentials:

Property name	Description
`credential-provider.type`	Type of the credential provider. Must be one of `INLINE`, `FILE`, or `KEYSTORE`; defaults to `INLINE`.
`connection-user`	Connection user name.
`connection-password`	Connection password.
`user-credential-name`	Name of the extra credentials property, whose value to use as the user name. See `extraCredentials` in Parameter reference.
`password-credential-name`	Name of the extra credentials property, whose value to use as the password.
`connection-credential-file`	Location of the properties file where credentials are present. It must contain the `connection-user` and `connection-password` properties.
`keystore-file-path`	The location of the Java Keystore file, from which to read credentials.
`keystore-type`	File format of the keystore file, for example `JKS` or `PEM`.
`keystore-password`	Password for the key store.
`keystore-user-credential-name`	Name of the key store entity to use as the user name.
`keystore-user-credential-password`	Password for the user name key store entity.
`keystore-password-credential-name`	Name of the key store entity to use as the password.
`keystore-password-credential-password`	Password for the password key store entity.

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.config-file.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`
`dynamic-filtering.enabled`	Push down dynamic filters into JDBC queries	`true`
`dynamic-filtering.wait-timeout`	Maximum duration for which Trino will wait for dynamic filters to be collected from the build side of joins before starting a JDBC query. Using a large timeout can potentially result in more detailed dynamic filters. However, it can also increase latency for some queries.	`20s`

Domain compaction threshold#

Pushing down a large list of predicates to the data source can compromise performance. Trino compacts large predicates into a simpler range predicate by default to ensure a balance between performance and predicate pushdown. If necessary, the threshold for this compaction can be increased to improve performance when the data source is capable of taking advantage of large predicates. Increasing this threshold may improve pushdown of large dynamic filters. The domain-compaction-threshold catalog configuration property or the domain_compaction_threshold catalog session property can be used to adjust the default value of 32 for this threshold.

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. 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.

Querying MariaDB#

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

SHOW SCHEMAS FROM mariadb;

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

SHOW TABLES FROM mariadb.web;

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

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

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

SELECT * FROM mariadb.web.clicks;

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

Type mapping#

Because Trino and MariaDB each support types that the other does not, this connector modifies some types when reading or writing data. Data types may not map the same way in both directions between Trino and the data source. Refer to the following sections for type mapping in each direction.

MariaDB type to Trino type mapping#

The connector maps MariaDB types to the corresponding Trino types according to the following table:

MariaDB type to Trino type mapping#
MariaDB type	Trino type	Notes
`BOOLEAN`	`TINYINT`	`BOOL` and `BOOLEAN` are aliases of `TINYINT(1)`
`TINYINT`	`TINYINT`
`SMALLINT`	`SMALLINT`
`INT`	`INTEGER`
`BIGINT`	`BIGINT`
`FLOAT`	`REAL`
`DOUBLE`	`DOUBLE`
`DECIMAL(p,s)`	`DECIMAL(p,s)`
`CHAR(n)`	`CHAR(n)`
`TINYTEXT`	`VARCHAR(255)`
`TEXT`	`VARCHAR(65535)`
`MEDIUMTEXT`	`VARCHAR(16777215)`
`LONGTEXT`	`VARCHAR`
`VARCHAR(n)`	`VARCHAR(n)`
`TINYBLOB`	`VARBINARY`
`BLOB`	`VARBINARY`
`MEDIUMBLOB`	`VARBINARY`
`LONGBLOB`	`VARBINARY`
`VARBINARY(n)`	`VARBINARY`
`DATE`	`DATE`
`TIME(n)`	`TIME(n)`
`TIMESTAMP(n)`	`TIMESTAMP(n)`	MariaDB stores the current timestamp by default. Enable explicit_defaults_for_timestamp to avoid implicit default values and use `NULL` as the default value.

No other types are supported.

Trino type mapping to MariaDB type mapping#

The connector maps Trino types to the corresponding MariaDB types according to the following table:

Trino type mapping to MariaDB type mapping#
Trino type	MariaDB type	Notes
`BOOLEAN`	`BOOLEAN`
`TINYINT`	`TINYINT`
`SMALLINT`	`SMALLINT`
`INTEGER`	`INT`
`BIGINT`	`BIGINT`
`REAL`	`FLOAT`
`DOUBLE`	`DOUBLE`
`DECIMAL(p,s)`	`DECIMAL(p,s)`
`CHAR(n)`	`CHAR(n)`
`VARCHAR(255)`	`TINYTEXT`	Maps on `VARCHAR` of length 255 or less.
`VARCHAR(65535)`	`TEXT`	Maps on `VARCHAR` of length between 256 and 65535, inclusive.
`VARCHAR(16777215)`	`MEDIUMTEXT`	Maps on `VARCHAR` of length between 65536 and 16777215, inclusive.
`VARCHAR`	`LONGTEXT`	`VARCHAR` of length greater than 16777215 and unbounded `VARCHAR` map to `LONGTEXT`.
`VARBINARY`	`MEDIUMBLOB`
`DATE`	`DATE`
`TIME(n)`	`TIME(n)`
`TIMESTAMP(n)`	`TIMESTAMP(n)`	MariaDB stores the current timestamp by default. Enable explicit_defaults_for_timestamp to avoid implicit default values and use `NULL` as the default value.

No other types are supported.

Complete list of MariaDB data types.

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 unbounded VARCHAR.

The respective catalog session property is unsupported_type_handling.

IGNORE

jdbc-types-mapped-to-varchar

Allow forced mapping of comma separated lists of data types to convert to unbounded VARCHAR

SQL support#

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

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.

Table functions#

The connector provides specific table functions to access MariaDB.

`query(varchar) -> table`#

The query function allows you to query the underlying database directly. It requires syntax native to MariaDB, because the full query is pushed down and processed in MariaDB. This can be useful for accessing native features which are not available in Trino or for improving query performance in situations where running a query natively may be faster.

Примечание

Polymorphic table functions may not preserve the order of the query result. If the table function contains a query with an ORDER BY clause, the function result may not be ordered as expected.

As an example, select the age of employees by using TIMESTAMPDIFF and CURDATE:

SELECT
  age
FROM
  TABLE(
    mariadb.system.query(
      query => 'SELECT
        TIMESTAMPDIFF(
          YEAR,
          date_of_birth,
          CURDATE()
        ) AS age
      FROM
        tiny.employees'
    )
  );

Performance#

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

Pushdown#

The connector supports pushdown for a number of operations:

Aggregate pushdown for the following functions:

Predicate pushdown support#

The connector does not support pushdown of any predicates on columns with textual 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';