SingleStore (MemSQL) connector

The SingleStore (formerly known as MemSQL) connector allows querying and creating tables in an external SingleStore database.

Requirements

To connect to SingleStore, you need:

• SingleStore version 7.1.4 or higher.
• Network access from the Trino coordinator and workers to SingleStore. Port 3306 is the default port.

Configuration

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

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

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

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.

Enable TLS between your cluster and SingleStore by appending the useSsl=true parameter to the connection-url configuration property:

connection-url=jdbc:singlestore://example.net:3306/?useSsl=true

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

Multiple SingleStore servers

You can have as many catalogs as you need, so if you have additional SingleStore 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 will create 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.

Querying SingleStore

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

SHOW SCHEMAS FROM singlestore;

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

SHOW TABLES FROM singlestore.web;

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

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

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

SELECT * FROM singlestore.web.clicks;

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

Type mapping

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

SQL support

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

• INSERT
• DELETE
• TRUNCATE
• CREATE TABLE
• CREATE TABLE
• DROP TABLE
• ALTER 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.

ALTER TABLE

The connector does not support renaming tables across multiple schemas. For example, the following statement is supported:

ALTER TABLE catalog.schema_one.table_one RENAME TO catalog.schema_one.table_two

The following statement attempts to rename a table across schemas, and therefore is not supported:

ALTER TABLE catalog.schema_one.table_one RENAME TO catalog.schema_two.table_two

Performance

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

Pushdown

The connector supports pushdown for a number of operations:

• Pushdown
• Pushdown
• Pushdown

Join pushdown

The join-pushdown.enabled catalog configuration property or join_pushdown_enabled catalog session property <session-properties-definition> control whether the connector pushes down join operations. The property defaults to false, and enabling join pushdowns may negatively impact performance for some queries.

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';