SingleStore 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, example.properties, to mount the SingleStore connector as the example 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
`case-insensitive-name-matching`	Support case insensitive schema and table names. Defaults to `false`.
`case-insensitive-name-matching.cache-ttl`	Duration for which case insensitive schema and table names are cached. Defaults to `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. Defaults to `null`.
`case-insensitive-name-matching.config-file.refresh-period`	Frequency with which Trino checks the name matching configuration file for changes. The duration value defaults to `0s` (refresh disabled).
`metadata.cache-ttl`	Duration for which metadata, including table and column statistics, is cached. Defaults to `0s` (caching disabled).
`metadata.cache-missing`	Cache the fact that metadata, including table and column statistics, is not available. Defaults to `false`.
`metadata.schemas.cache-ttl`	Duration for which schema metadata is cached. Defaults to the value of `metadata.cache-ttl`.
`metadata.tables.cache-ttl`	Duration for which table metadata is cached. Defaults to the value of `metadata.cache-ttl`.
`metadata.statistics.cache-ttl`	Duration for which tables statistics are cached. Defaults to the value of `metadata.cache-ttl`.
`metadata.cache-maximum-size`	Maximum number of objects stored in the metadata cache. Defaults to `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. Defaults to `1000`.
`dynamic-filtering.enabled`	Push down dynamic filters into JDBC queries. Defaults to `true`.
`dynamic-filtering.wait-timeout`	Maximum duration for which Trino waits 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. Defaults to `20s`.

Appending query metadata#

The optional parameter query.comment-format allows you to configure a SQL comment that is sent to the datasource with each query. The format of this comment can contain any characters and the following metadata:

$QUERY_ID: The identifier of the query.
$USER: The name of the user who submits the query to Trino.
$SOURCE: The identifier of the client tool used to submit the query, for example trino-cli.
$TRACE_TOKEN: The trace token configured with the client tool.

The comment can provide more context about the query. This additional information is available in the logs of the datasource. To include environment variables from the Trino cluster with the comment , use the ${ENV:VARIABLE-NAME} syntax.

The following example sets a simple comment that identifies each query sent by Trino:

query.comment-format=Query sent by Trino.

With this configuration, a query such as SELECT * FROM example_table; is sent to the datasource with the comment appended:

SELECT * FROM example_table; /*Query sent by Trino.*/

The following example improves on the preceding example by using metadata:

query.comment-format=Query $QUERY_ID sent by user $USER from Trino.

If Jane sent the query with the query identifier 20230622_180528_00000_bkizg, the following comment string is sent to the datasource:

SELECT * FROM example_table; /*Query 20230622_180528_00000_bkizg sent by user Jane from Trino.*/

Note

Certain JDBC driver settings and logging configurations might cause the comment to be removed.

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.

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.example_schema;
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. 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 example;

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

SHOW TABLES FROM example.web;

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

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

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

SELECT * FROM example.web.clicks;

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

Type mapping#

Because Trino and Singlestore 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.

Singlestore to Trino type mapping#

The connector maps Singlestore types to the corresponding Trino types following this table:

Singlestore to Trino type mapping#
Singlestore type	Trino type	Notes
`BIT`	`BOOLEAN`
`BOOLEAN`	`BOOLEAN`
`TINYINT`	`TINYINT`
`TINYINT UNSIGNED`	`SMALLINT`
`SMALLINT`	`SMALLINT`
`SMALLINT UNSIGNED`	`INTEGER`
`INTEGER`	`INTEGER`
`INTEGER UNSIGNED`	`BIGINT`
`BIGINT`	`BIGINT`
`BIGINT UNSIGNED`	`DECIMAL(20, 0)`
`DOUBLE`	`DOUBLE`
`REAL`	`DOUBLE`
`DECIMAL(p, s)`	`DECIMAL(p, s)`	See Singlestore DECIMAL type handling
`CHAR(n)`	`CHAR(n)`
`TINYTEXT`	`VARCHAR(255)`
`TEXT`	`VARCHAR(65535)`
`MEDIUMTEXT`	`VARCHAR(16777215)`
`LONGTEXT`	`VARCHAR`
`VARCHAR(n)`	`VARCHAR(n)`
`LONGBLOB`	`VARBINARY`
`DATE`	`DATE`
`TIME`	`TIME(0)`
`TIME(6)`	`TIME(6)`
`DATETIME`	`TIMESTAMP(0)`
`DATETIME(6)`	`TIMESTAMP(6)`
`JSON`	`JSON`

No other types are supported.

Trino to Singlestore type mapping#

The connector maps Trino types to the corresponding Singlestore types following this table:

Trino to Singlestore type mapping#
Trino type	Singlestore type	Notes
`BOOLEAN`	`BOOLEAN`
`TINYINT`	`TINYINT`
`SMALLINT`	`SMALLINT`
`INTEGER`	`INTEGER`
`BIGINT`	`BIGINT`
`DOUBLE`	`DOUBLE`
`REAL`	`FLOAT`
`DECIMAL(p, s)`	`DECIMAL(p, s)`	See Singlestore DECIMAL type handling
`CHAR(n)`	`CHAR(n)`
`VARCHAR(65535)`	`TEXT`
`VARCHAR(16777215)`	`MEDIUMTEXT`
`VARCHAR`	`LONGTEXT`
`VARCHAR(n)`	`VARCHAR(n)`
`VARBINARY`	`LONGBLOB`
`DATE`	`DATE`
`TIME(0)`	`TIME`
`TIME(6)`	`TIME(6)`
`TIMESTAMP(0)`	`DATETIME`
`TIMESTAMP(6)`	`DATETIME(6)`
`JSON`	`JSON`

No other types are supported.

Decimal type handling#

DECIMAL types with unspecified precision or scale are mapped to a Trino DECIMAL with a default precision of 38 and default scale of 0. The scale can be changed 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 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 SingleStore database. In addition to the globally available and read operation statements, the connector supports the following features:

UPDATE#

Only UPDATE statements with constant assignments and predicates are supported. For example, the following statement is supported because the values assigned are constants:

UPDATE table SET col1 = 1 WHERE col3 = 1

Arithmetic expressions, function calls, and other non-constant UPDATE statements are not supported. For example, the following statement is not supported because arithmetic expressions cannot be used with the SET command:

UPDATE table SET col1 = col2 + 2 WHERE col3 = 1

The =, !=, >, <, >=, <=, IN, NOT IN operators are supported in predicates. The following statement is not supported because the AND operator cannot be used in predicates:

UPDATE table SET col1 = 1 WHERE col3 = 1 AND col2 = 3

All column values of a table row cannot be updated simultaneously. For a three column table, the following statement is not supported:

UPDATE table SET col1 = 1, col2 = 2, col3 = 3 WHERE col3 = 1

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 RENAME TO#

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

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

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

ALTER TABLE example.schema_one.table_one RENAME TO example.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:

Note

The connector performs pushdown where performance may be improved, but in order to preserve correctness an operation may not be pushed down. When pushdown of an operation may result in better performance but risks correctness, the connector prioritizes correctness.

Join pushdown#

The join-pushdown.enabled catalog configuration property or join_pushdown_enabled catalog session property 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 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';