Redis connector#

The Redis connector allows querying of live data stored in Redis. This can be used to join data between different systems like Redis and Hive.

Each Redis key/value pair is presented as a single row in Trino. Rows can be broken down into cells by using table definition files.

Currently, only Redis key of string and zset types are supported, only Redis value of string and hash types are supported.

Requirements#

Requirements for using the connector in a catalog to connect to a Redis data source are:

  • Redis 2.8.0 or higher (Redis Cluster is not supported)

  • Network access, by default on port 6379, from the Trino coordinator and workers to Redis.

Configuration#

To configure the Redis connector, create a catalog properties file etc/catalog/redis.properties with the following content, replacing the properties as appropriate:

connector.name=redis
redis.table-names=schema1.table1,schema1.table2
redis.nodes=host:port

Multiple Redis servers#

You can have as many catalogs as you need. If you have additional Redis servers, simply add another properties file to etc/catalog with a different name, making sure it ends in .properties.

Configuration properties#

The following configuration properties are available:

Property Name

Description

redis.table-names

List of all tables provided by the catalog

redis.default-schema

Default schema name for tables

redis.nodes

Location of the Redis server

redis.scan-count

Redis parameter for scanning of the keys

redis.max-keys-per-fetch

Get values associated with the specified number of keys in the redis command such as MGET(key…)

redis.key-prefix-schema-table

Redis keys have schema-name:table-name prefix

redis.key-delimiter

Delimiter separating schema_name and table_name if redis.key-prefix-schema-table is used

redis.table-description-dir

Directory containing table description files

redis.table-description-cache-ttl

The cache time for table description files

redis.hide-internal-columns

Controls whether internal columns are part of the table schema or not

redis.database-index

Redis database index

redis.user

Redis server username

redis.password

Redis server password

redis.table-names#

Comma-separated list of all tables provided by this catalog. A table name can be unqualified (simple name) and is placed into the default schema (see below), or qualified with a schema name (<schema-name>.<table-name>).

For each table defined, a table description file (see below) may exist. If no table description file exists, the table only contains internal columns (see below).

This property is optional; the connector relies on the table description files specified in the redis.table-description-dir property.

redis.default-schema#

Defines the schema which will contain all tables that were defined without a qualifying schema name.

This property is optional; the default is default.

redis.nodes#

The hostname:port pair for the Redis server.

This property is required; there is no default.

Redis Cluster is not supported.

redis.scan-count#

The internal COUNT parameter for the Redis SCAN command when connector is using SCAN to find keys for the data. This parameter can be used to tune performance of the Redis connector.

This property is optional; the default is 100.

redis.max-keys-per-fetch#

The internal number of keys for the Redis MGET command and Pipeline HGETALL command when connector is using these commands to find values of keys. This parameter can be used to tune performance of the Redis connector.

This property is optional; the default is 100.

redis.key-prefix-schema-table#

If true, only keys prefixed with the schema-name:table-name are scanned for a table, and all other keys are filtered out. If false, all keys are scanned.

This property is optional; the default is false.

redis.key-delimiter#

The character used for separating schema-name and table-name when redis.key-prefix-schema-table is true

This property is optional; the default is :.

redis.table-description-dir#

References a folder within Trino deployment that holds one or more JSON files, which must end with .json and contain table description files.

Note that the table description files will only be used by the Trino coordinator node.

This property is optional; the default is etc/redis.

redis.table-description-cache-ttl#

The Redis connector dynamically loads the table description files after waiting for the time specified by this property. Therefore, there is no need to update the redis.table-names property and restart the Trino service when adding, updating, or deleting a file end with .json to redis.table-description-dir folder.

This property is optional; the default is 5m.

redis.hide-internal-columns#

In addition to the data columns defined in a table description file, the connector maintains a number of additional columns for each table. If these columns are hidden, they can still be used in queries, but they do not show up in DESCRIBE <table-name> or SELECT *.

This property is optional; the default is true.

redis.database-index#

The Redis database to query.

This property is optional; the default is 0.

redis.user#

The username for Redis server.

This property is optional; the default is null.

redis.password#

The password for password-protected Redis server.

This property is optional; the default is null.

Internal columns#

For each defined table, the connector maintains the following columns:

Column name

Type

Description

_key

VARCHAR

Redis key.

_value

VARCHAR

Redis value corresponding to the key.

_key_length

BIGINT

Number of bytes in the key.

_value_length

BIGINT

Number of bytes in the value.

_key_corrupt

BOOLEAN

True if the decoder could not decode the key for this row. When true, data columns mapped from the key should be treated as invalid.

_value_corrupt

BOOLEAN

True if the decoder could not decode the message for this row. When true, data columns mapped from the value should be treated as invalid.

For tables without a table definition file, the _key_corrupt and _value_corrupt columns are false.

Table definition files#

With the Redis connector it is possible to further reduce Redis key/value pairs into granular cells, provided the key/value string follows a particular format. This process defines new columns that can be further queried from Trino.

A table definition file consists of a JSON definition for a table. The name of the file can be arbitrary, but must end in .json.

{
    "tableName": ...,
    "schemaName": ...,
    "key": {
        "dataFormat": ...,
        "fields": [
            ...
        ]
    },
    "value": {
        "dataFormat": ...,
        "fields": [
            ...
       ]
    }
}

Field

Required

Type

Description

tableName

required

string

Trino table name defined by this file.

schemaName

optional

string

Schema which will contain the table. If omitted, the default schema name is used.

key

optional

JSON object

Field definitions for data columns mapped to the value key.

value

optional

JSON object

Field definitions for data columns mapped to the value itself.

Please refer to the Kafka connector page for the description of the dataFormat as well as various available decoders.

In addition to the above Kafka types, the Redis connector supports hash type for the value field which represent data stored in the Redis hash.

{
    "tableName": ...,
    "schemaName": ...,
    "value": {
        "dataFormat": "hash",
        "fields": [
            ...
       ]
    }
}

SQL support#

The connector provides globally available and read operation statements to access data and metadata in Redis.

Performance#

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

Pushdown#

Predicate pushdown support#

The connector supports pushdown of keys, only Redis key of string type supports pushdown, the zset type does not support. Currently, key pushdown is not supported when multiple key fields are defined in the table definition file.

The connector supports pushdown of equality predicates, such as IN or =. Range predicates, such as >, <, or BETWEEN, and inequality predicates, such as != are not pushed down.

In the following example, the predicate of the first query is not pushed down since > is a range predicate. The other queries are pushed down.

-- Not pushed down
SELECT * FROM nation WHERE redis_key > 'CANADA';
-- Pushed down
SELECT * FROM nation WHERE redis_key = 'CANADA';
SELECT * FROM nation WHERE redis_key IN ('CANADA', 'POLAND');