Starburst Snowflake connector#

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

Requirements#

To connect to Snowflake, you need:

Configuration#

To configure the Snowflake connector, create a catalog properties file in etc/catalog named, for example, snowflake.properties, to mount the Snowflake connector as the snowflake catalog.

There are two flavors of the Snowflake connector:

  • snowflake-jdbc

  • snowflake-distributed

snowflake-jdbc uses JDBC for all reads and writes and is more efficient when the result set returned from Snowflake is small.

When larger result sets are extracted from Snowflake, the snowflake-distributed connector may be a better choice. Instead of requesting query results over a JDBC connection, the connector asks Snowflake to export them to object storage and SEP reads them from there. Since write and read operations are parallelized, this approach scales better for large data sets, but has a higher latency.

A requirement of using the distributed connector is that your Snowflake deployment runs on AWS or Azure. The connector automatically creates temporary stages in temporary storage buckets using Snowflake.

Create the catalog properties file with the following contents, replacing the connection properties as appropriate for your setup (for example, replace <account_name> with the full name of your account, as provided by Snowflake).

For AWS:

connector.name=<snowflake-jdbc or snowflake-distributed>
connection-url=jdbc:snowflake://<account_name>.snowflakecomputing.com/
connection-user=<user_name>
connection-password=<password>
snowflake.warehouse=<warehouse_name>
snowflake.database=<database_name>

For Azure:

connector.name=<snowflake-jdbc or snowflake-distributed>
connection-url=jdbc:snowflake://<account_name>.<azure_region>.azure.snowflakecomputing.com/
connection-user=<user_name>
connection-password=<password>
snowflake.warehouse=<warehouse_name>
snowflake.database=<database_name>

The role used by Snowflake to execute operations can be specified as snowflake.role=<role_name>. This configuration is optional, and can not be used together with User impersonation.

Additionally, there are a number of configuration properties that apply only to the distributed connector.

Distributed connector configuration properties#

Property name

Description

Default

snowflake.stage-schema

Name of the schema in which stages are created for exporting data

snowflake.max-export-retries

Number of export retries

3

snowflake.parquet.max-read-block-size

Maximum block size when reading from the export file

16MB

snowflake.max-split-size

Maximum split size for processing the export file

64MB

snowflake.max-initial-split-size

Maximum initial split size

Half of snowflake.max-split-size

snowflake.export-file-max-size

Maximum size of files to create when exporting data

16MB

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

join-pushdown.enabled

Enable join pushdown. Equivalent catalog session property is join_pushdown_enabled. Enabling this may negatively impact performance for some queries.

false

Type mapping#

Snowflake and SEP support different types. The Snowflake connectors uses the type mapping in the following sections for reading and writing data. Other types are not supported.

Snowflake to SEP read type mapping#

SEP supports reading Snowflake types. This table shows the Snowflake to SEP read type mapping:

Snowflake to SEP type mapping for read operations#

Snowflake type

SEP type

Notes

BOOLEAN

BOOLEAN

NUMBER(p, s)

DECIMAL(p, s)

FLOAT

DOUBLE

DOUBLE

DOUBLE

DOUBLE PRECISION

DOUBLE

REAL

REAL

TINYINT

TINYINT

SMALLINT

SMALLINT

INTEGER

INTEGER

BIGINT

BIGINT

VARIANT

VARCHAR(max)

CHAR(n)

CHAR(n)

VARCHAR(n)

VARCHAR(n)

VARBINARY(n)

VARBINARY(n)

OBJECT

VARCHAR(max)

ARRAY

VARCHAR(max)

DATE

DATE

TIME

TIME

TIMESTAMP_NTZ(n)

TIMESTAMP(n)

Supports only precision 3 in distributed mode

TIMESTAMP_LTZ(n)

TIMESTAMP(n) WITH TIME ZONE

Supports only precision 3 in distributed mode

TIMESTAMP_TZ(n)

TIMESTAMP(n) WITH TIME ZONE

Supports only precision 3 in distributed mode

TIMESTAMP(n)

TIMESTAMP(n)

Supports only precision 3 in distributed mode

SEP to Snowflake write type mapping#

SEP supports creating tables and writing data with the following types in Snowflake. The table shows the mappings from SEP to Snowflake types:

SEP to Snowflake type mapping for write operations#

Trino type

Snowflake type

Notes

BOOLEAN

BOOLEAN

DECIMAL(p, s)

NUMBER(p, s)

DOUBLE

DOUBLE

DOUBLE

DOUBLE PRECISION

REAL

REAL

TINYINT

NUMBER(3)

SMALLINT

NUMBER(5)

INTEGER

NUMBER(10)

BIGINT

NUMBER(19)

CHAR(n)

CHAR(n)

VARCHAR(n)

VARCHAR(n)

VARBINARY(n)

VARBINARY(n)

DATE

DATE

TIME

TIME

TIMESTAMP(n)

TIMESTAMP_NTZ(n)

TIMESTAMP(n) WITH TIME ZONE

TIMESTAMP_TZ(n)

General 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 and write access to data and metadata in the Snowflake 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.

Performance#

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

Table statistics#

The Snowflake connector supports only table statistics to improve query processing performance based on the actual data in the data source.

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

They are based on Snowflake’s INFORMATION_SCHEMA.TABLES table. Table statistics are automatically updated by Snowflake.

Pushdown#

The connector supports pushdown for a number of operations:

Aggregate pushdown for the following functions:

Dynamic filtering#

Dynamic filtering is enabled by default. It causes the connector to wait for dynamic filtering to complete before starting a JDBC query.

You can disable dynamic filtering by setting the property dynamic-filtering.enabled in your catalog properties file to false.

JDBC connection pooling#

You can improve performance by enabling JDBC connection pooling, which is disabled by default.

Starburst Cached Views#

The connectors supports table scan redirection to improve performance and reduce load on the data source.

Security#

The connector includes a number of security-related features, detailed in the following sections.

User impersonation#

The Snowflake connector supports User impersonation. It can be configured to use a number of different impersonation mechanisms, specified by the values configured for the property snowflake.impersonation-type:

snowflake.impersonation-type=ROLE
NONE

Connect as the service user with the credentials from the catalog properties file and assume the role defined by the snowflake.role property, or the service user’s default role, if the property is missing.

ROLE

Connect as the service user and use auth-to-local mapping to map the user to a role.

OKTA_LDAP_PASSTHROUGH

Assume the identity of the SEP user, authenticated with Okta using LDAP credentials, and use the default Snowflake user role.

ROLE_OKTA_LDAP_PASSTHROUGH

As above, but additionally use auth-to-local mapping to map the user to a role.

Note

Impersonation using Okta is not supported for Azure.

Authentication with Okta#

The Snowflake connector supports the usage of the Okta Single Sign-On system to authenticate users via SEP to Snowflake.

Note

Okta authentication is not supported for Azure.

The setup allows users to authenticate to SEP using their LDAP credentials and use the same credentials to authenticate to Snowflake through Okta. The same credentials are used by SEP when accessing data in Snowflake.

Behind the scenes SEP and the Snowflake connector authenticate to Okta with the LDAP credentials of the user. After the user authenticates with Okta, including MFA potentially, a SAML assertion allows Snowflake to issue an an OAuth 2.0 token pair. The tokens are cached in SEP and used for further authentications until they expire, and another authentication is requested.

If Okta multi-factor authentication (MFA) is configured, users have to confirm authentication with it. One time codes are not supported.

To enable the Okta integration, SEP and Snowflake need to be configured correctly.

Okta and SEP are configured to use LDAP authentication using the same user identifiers and LDAP directory. In addition to the usual LDAP configuration, LDAP authentication, for SEP, you need to enable password forwarding in etc/config.properties:

http.server.authentication.password.forwarding-enabled=true

Snowflake is configured in Okta as a SAML application as detailed in the Snowflake documentation. Note that the Snowflake login_name must match the corresponding SAML Subject NameID attribute value.

SEP is configured as an OAuth client in Snowflake, again detailed in the Snowflake OAuth documentation.

A number of properties are required to configure the Okta integration in the Snowflake catalog properties file:

snowflake.account-name

Name of Snowflake account.

snowflake.account-url

URL of the Snowflake account. The URL usually has the form https://account_name.snowflakecomputing.com, but might include additional segments.

snowflake.client-id

Snowflake OAuth client id. This can be retrieved with the secret name and a query like select system$show_oauth_client_secrets('OAUTH_TEST_INT');.

snowflake.client-secret

Snowflake OAuth client secret.

snowflake.credential.cache-ttl

Duration the OAuth refresh token is cached. This value cannot exceed the oauth_refresh_token_validity value used when the OAuth integration was created. E.g. 24h.

okta.account-url

The Okta URL, typically https://your_okta_account_name.okta.com).

Optional properties allow you to override the default values:

snowflake.credential.cache-size

The size of the OAuth credentials cache. Use a value that accommodates the expected number of users that might connect to Snowflake through SEP during the period defined by the TTL of the token. Defaults to 10000.

snowflake.credential.http-connect-timeout

Connection timeout. Defaults to 30s.

snowflake.credential.http-read-timeout

Connection read timeout. Defaults to 30s.

snowflake.credential.http-write-timeout

Connection write timeout. Defaults to 30s.

snowflake.redirect-uri

The redirect URI for OAUTH. Value must match the redirect URI specified when creating the security integration (oauth_redirect_uri). Defaults to https://localhost.

okta.credential.http-connect-timeout

Connection timeout. Defaults to 30s.

okta.credential.http-read-timeout

Connection read timeout. Defaults to 30s.

okta.credential.http-write-timeout

Connection write timeout. Defaults to 30s.

OAuth 2.0 token pass-through#

The Snowflake connector supports OAuth 2.0 token pass-through.

Configure this option the same as Authentication with Okta, except for the settings described in this section.

Set the authentication type and OAuth 2.0 scope in the coordinator’s config properties file:

http-server.authentication.type=DELEGATED_OAUTH2
http-server.authentication.oauth2.scopes=<EXISTING_SCOPES>,session:role:TEST_ROLE

The session:role prefix determines the role assigned to the user after successful authentication.

Additionally enable OAUTH2_PASSTHROUGH in the catalog properties file using the Snowflake connector:

snowflake.impersonation-type=OAUTH2_PASSTHROUGH