Database

Redis


Redis is an open-source in-memory storage, used as a distributed, in-memory key–value database, cache and message broker, with optional durability.

The Redis Wrapper allows you to read data from Redis within your Postgres database.

Preparation

Before you can query Redis, you need to enable the Wrappers extension and store your credentials in Postgres.

Enable Wrappers

Make sure the wrappers extension is installed on your database:

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create extension if not exists wrappers with schema extensions;

Enable the Redis Wrapper

Enable the redis_wrapper FDW:

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create foreign data wrapper redis_wrapper handler redis_fdw_handler validator redis_fdw_validator;

Store your credentials (optional)

By default, Postgres stores FDW credentials inside pg_catalog.pg_foreign_server in plain text. Anyone with access to this table will be able to view these credentials. Wrappers is designed to work with Vault, which provides an additional level of security for storing credentials. We recommend using Vault to store your credentials.

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-- Save your Redis connection URL in Vault and retrieve the `key_id`insert into vault.secrets (name, secret)values ( 'redis_conn_url', 'redis://username:password@127.0.0.1:6379/db')returning key_id;

Connecting to Redis

We need to provide Postgres with the credentials to connect to Redis. We can do this using the create server command:

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create server redis_server foreign data wrapper redis_wrapper options ( conn_url_id '<key_ID>' -- The Key ID from above. );

Create a schema

We recommend creating a schema to hold all the foreign tables:

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create schema if not exists redis;

Options

The following options are available when creating Redis foreign tables:

  • src_type - Foreign table source type in Redis, required.

This can be one of below types,

Source typeDescription
listSingle list
setSingle set
hashSingle hash
zsetSingle sorted set
streamStream
multi_listMultiple lists, specified by src_key pattern
multi_setMultiple sets, specified by src_key pattern
multi_hashMultiple hashes, specified by src_key pattern
multi_zsetMultiple sorted sets, specified by src_key pattern
  • src_key - Source object key in Redis, required.

This key can be a pattern for multi_* type of foreign table. For other types, this key must return exact one value. For example,

Source Typesrc_key examples
list, set, hash, zset, streammy_list, list:001, hash_foo, zset:1000 and etc.
multi_list, multi_set, multi_hash, multi_zsetmy_list:*, set:*, zset:* and etc.

Entities

List

This is an object representing a Redis List.

Ref: Redis docs

Operations

ObjectSelectInsertUpdateDeleteTruncate
List

Usage

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create foreign table redis.list ( element text) server redis_server options ( src_type 'list', src_key 'my_list' );

Notes

  • Elements are stored in insertion order
  • Query returns all elements in the list
  • No query pushdown support

Set

This is an object representing a Redis Set.

Ref: Redis docs

Operations

ObjectSelectInsertUpdateDeleteTruncate
Set

Usage

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create foreign table redis.set ( element text) server redis_server options ( src_type 'set', src_key 'set' );

Notes

  • Elements are unique within the set
  • No guaranteed order of elements
  • No query pushdown support

Hash

This is an object representing a Redis Hash.

Ref: Redis docs

Operations

ObjectSelectInsertUpdateDeleteTruncate
Hash

Usage

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create foreign table redis.hash ( key text, value text) server redis_server options ( src_type 'hash', src_key 'hash' );

Notes

  • Key-value pairs within the hash
  • No query pushdown support
  • Both key and value are returned as text

Sorted Set

This is an object representing a Redis Sorted Set.

Ref: Redis docs

Operations

ObjectSelectInsertUpdateDeleteTruncate
Sorted Set

Usage

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create foreign table redis.zset ( element text) server redis_server options ( src_type 'zset', src_key 'zset' );

Notes

  • Elements are ordered by their score
  • Elements are unique within the set
  • Score information is not exposed in the foreign table

Stream

This is an object representing a Redis Stream.

Ref: Redis docs

Operations

ObjectSelectInsertUpdateDeleteTruncate
Stream

Usage

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create foreign table redis.stream ( id text, items jsonb) server redis_server options ( src_type 'stream', src_key 'stream' );

Notes

  • Stream entries have unique IDs
  • Items are stored in JSONB format
  • Entries are ordered by their IDs

Multiple Objects

Redis wrapper supports querying multiple objects of the same type using pattern matching.

Operations

Object TypeSelectInsertUpdateDeleteTruncate
Multiple List
Multiple Set
Multiple Hash
Multiple ZSet

Usage

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create foreign table redis.multi_lists ( key text, items jsonb) server redis_server options ( src_type 'multi_list', src_key 'list:*' );

Notes

  • Use pattern matching in src_key option
  • Results include object key and items in JSONB format
  • Items format varies by object type

Query Pushdown Support

This FDW doesn't support pushdown.

Supported Redis Data Types

All Redis values will be stored as text or jsonb columns in Postgres, below are the supported Redis data types:

Redis TypeForeign Table Type (src_type)
Listlist
Setset
Hashhash
Sorted Setzset
Streamstream
Multiple Listmulti_list
Multiple Setmulti_set
Multiple Hashmulti_hash
Multiple Sorted Setmulti_zset

Limitations

This section describes important limitations and considerations when using this FDW:

  • Full result sets are loaded into memory before processing
  • Read-only access to Redis data structures (no Insert, Update, Delete, or Truncate operations)
  • Pattern matching in multi_* types only supports basic Redis glob patterns
  • Materialized views using these foreign tables may fail during logical backups

Examples

Some examples on how to use Redis foreign tables.

Let's prepare some source data in Redis CLI first:

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127.0.0.1:6379> RPUSH list foo bar 42127.0.0.1:6379> SADD set foo bar 42127.0.0.1:6379> HSET hash foo bar baz qux127.0.0.1:6379> ZADD zset 30 foo 20 bar 10 baz127.0.0.1:6379> XADD stream * foo bar127.0.0.1:6379> XADD stream * aa 42 bb 43127.0.0.1:6379> RPUSH list:100 foo bar127.0.0.1:6379> RPUSH list:200 baz127.0.0.1:6379> SADD set:100 foo127.0.0.1:6379> SADD set:200 bar127.0.0.1:6379> HSET hash:100 foo bar127.0.0.1:6379> HSET hash:200 baz qux127.0.0.1:6379> ZADD zset:100 10 foo 20 bar127.0.0.1:6379> ZADD zset:200 40 baz 30 qux

Basic example

This example will create foreign tables inside your Postgres database and query their data:

  • List

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    create foreign table redis.list ( element text)server redis_serveroptions ( src_type 'list', src_key 'list');select * from redis.list;

    Query result:

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    element--------- foo bar 42(3 rows)
  • Set

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    create foreign table redis.set ( element text)server redis_serveroptions ( src_type 'set', src_key 'set');select * from redis.set;

    Query result:

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    element--------- 42 foo bar(3 rows)
  • Hash

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    create foreign table redis.hash ( key text, value text)server redis_serveroptions ( src_type 'hash', src_key 'hash');select * from redis.hash;

    Query result:

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    key | value-----+------- foo | bar baz | qux(2 rows)
  • Sorted set

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    create foreign table redis.zset ( element text)server redis_serveroptions ( src_type 'zset', src_key 'zset');select * from redis.zset;

    Query result:

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    element--------- baz bar foo(3 rows)
  • Stream

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    create foreign table redis.stream ( id text, items jsonb)server redis_serveroptions ( src_type 'stream', src_key 'stream');select * from redis.stream;

    Query result:

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    id | items-----------------+-------------------------- 1704343825989-0 | {"foo": "bar"} 1704343829799-0 | {"aa": "42", "bb": "43"}(2 rows)

Query multiple objects example

This example will create several foreign tables using pattern in key and query multiple objects from Redis:

  • List

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    create foreign table redis.multi_lists ( key text, items jsonb) server redis_server options ( src_type 'multi_list', src_key 'list:*' );select * from redis.multi_lists;

    Query result:

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    key | items----------+---------------- list:100 | ["foo", "bar"] list:200 | ["baz"](2 rows)
  • Set

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    create foreign table redis.multi_sets ( key text, items jsonb) server redis_server options ( src_type 'multi_set', src_key 'set:*' );select * from redis.multi_sets;

    Query result:

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    key | items---------+--------- set:100 | ["foo"] set:200 | ["bar"](2 rows)
  • Hash

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    create foreign table redis.multi_hashes ( key text, items jsonb) server redis_server options ( src_type 'multi_hash', src_key 'hash:*' );select * from redis.multi_hashes;

    Query result:

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    key | items----------+---------------- hash:200 | {"baz": "qux"} hash:100 | {"foo": "bar"}(2 rows)
  • Sorted set

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    create foreign table redis.multi_zsets ( key text, items jsonb) server redis_server options ( src_type 'multi_zset', src_key 'zset:*' );select * from redis.multi_zsets;

    Query result:

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    key | items----------+---------------- zset:200 | ["qux", "baz"] zset:100 | ["foo", "bar"](2 rows)