# 7.19. 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 Presto. Rows can be broken down into cells by using table definition files.

Only Redis string and hash value types are supported; sets and zsets cannot be queried from Presto.

The connector requires Redis 2.8.0 or later.

## 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, so 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.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.hide-internal-columns Controls whether internal columns are part of the table schema or not
redis.database-index Redis database index
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 will be put into the default schema (see below) or qualified with a schema name (<schema-name>.<table-name>).

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

This property is required; there is no default and at least one table must be defined.

### 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 clusters are not supported.

### redis.scan-count

The internal COUNT parameter for 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.key-prefix-schema-table

If true, only keys prefixed with the schema-name:table-name: are scanned for a table, and all other keys will be filtered out. If false, all keys are scanned. Note that if the schema-name is default schema, then the prefix to be scanned is just table-name:.

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 Presto deployment that holds one or more JSON files (must end with .json) which contain table description files.

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

### 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 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.password

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 will always be false.

## Table Definition Files

With the Redis connector it’s possible to further reduce Redis key/value pairs into granular cells provided the key/value sting follow a particular format. This process will define new columns that can be further queried from Presto.

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 Presto 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": [
...
]
}
}