This library is a client to Redis, a popular key
value store to deal with caching and communication between micro
In the typical use case we register the details of one or more Redis
servers using redis_server/3. Subsequenly, redis/2-3 is used to issue
commands on the server. For example:
?- redis_server(default, redis:6379, [password("secret")]).
?- redis(default, set(user, "Bob")).
?- redis(default, get(user), User).
User = "Bob"
- redis_server(+ServerName, +Address, +Options) is det
- Register a redis server without connecting to it. The ServerName
acts as a lazy connection alias. Initially the ServerName
localhost:6379 with no connect options. The
server is used for redis/1 and redis/2 and may be changed using this
predicate. Options are described with redis_connect/3.
Connections established this way are by default automatically
reconnected if the connection is lost for some reason unless a
reconnect(false) option is specified.
- redis_connect(-Connection) is det
- redis_connect(+Address, -Connection, +Options) is det
- redis_connect(-Connection, +Host, +Port) is det
- Connect to a redis server. The main mode is
-Connection, +Options). redis_connect/1 is equivalent to
redis_connect(localhost:6379, Connection, ). Options:
true, try to reconnect to the service when the connection
seems lost. Default is
true for connections specified using
false for explictly opened connections.
password(Password) are specified, these
are used to authenticate using the HELLO command.
- Authenticate using Password
- Specify the connection protocol version. Initially this is
version 2. Redis 6 also supports version 3. When specified
3, the HELLO command is used to upgrade the protocol.
Instead of using these predicates, redis/2 and redis/3 are normally
used with a server name argument registered using redis_server/3.
These predicates are meant for creating a temporary paralel
connection or using a connection with a blocking call.
|Address||- is a term Host:Port, |
unix(File) or the name of a server
registered using redis_server/3. The latter realises a new
connection that is typically used for blocking redis commands such
as listening for published messages, waiting on a list or stream.
redis_connect(-Connection, +Host, +Port) provides
compatibility to the original GNU-Prolog interface and is equivalent
redis_connect(Host:Port, Connection, ).
- do_connect(+Id, +Address, -Conn, +Options)[private]
- Open the connection. A connection is a compound term of the shape
redis_connection(Id, Stream, Failures, Options)
- hello(+Connection, +Option)[private]
- Initialize the connection. This is used to upgrade to the RESP3
protocol and/or to authenticate.
- redis_stream(+Spec, --Stream, +DoConnect) is det[private]
- Get the stream to a Redis server from Spec. Spec is either the name
of a registered server or a term
redis_connection(Id,Stream,Failures,Options). If the stream is
disconnected it will be reconnected.
- redis_disconnect(+Connection) is det
- redis_disconnect(+Connection, +Options) is det
- Disconnect from a redis server. The second form takes one option,
similar to close/2:
false), do not raise any errors if
Connection does not exist or closing the connection raises
a network or I/O related exception. This version is used
internally if a connection is in a broken state, either due
to a protocol error or a network issue.
- redis(+Connection, +Request) is semidet
- This predicate is overloaded to handle two types of requests. First,
it is a shorthand for
redis(Connection, Command, _) and second, it
can be used to exploit Redis pipelines and transactions. The
second form is acticated if Request is a list. In that case, each
element of the list is either a term
Command -> Reply or a simple
Command. Semantically this represents a sequence of redis/3 and
redis/2 calls. It differs in the following aspects:
- All commands are sent in one batch, after which all replies are
read. This reduces the number of round trips and typically
greatly improves performance.
- If the first command is
multi and the last
commands are executed as a Redis transaction, i.e., they
are executed atomically.
- If one of the commands returns an error, the subsequent commands
are still executed.
- You can not use variables from commands earlier in the list for
commands later in the list as a result of the above execution
Procedurally, the process takes the following steps:
- Send all commands
- Read all replies and push messages
- Handle all callbacks from push messages
- Check whether one of the replies is an error. If so,
raise this error (subsequent errors are lost)
- Bind all replies for the
Command -> Reply terms.
lrange(li,0,-1) -> List
List = ["2", "1"].
- redis(+Connection, +Command, -Reply) is semidet
- Execute a redis Command on Connnection. Next, bind Reply to the
returned result. Command is a callable term whose functor is the
name of the Redis command and whose arguments are translated to
Redis arguments according to the rules below. Note that all text is
always represented using UTF-8 encoding.
- Atomic values are emitted verbatim
- A term A:B:... where all arguments are either atoms,
strings or integers (no floats) is translated into
"A:B:...". This is a common shorthand for
representing Redis keys.
- A term Term as prolog is emitted as "\u0000T\u0000" followed
by Term in canonical form.
- Any other term is emitted as write/1.
Reply is either a plain term (often a variable) or a term
Type. In the latter form, Type dictates how the Redis bulk
reply is translated to Prolog. The default equals to
as a number of the content satisfies the Prolog number syntax and
as an atom otherwise.
Returned if the server replies with
+ Status. Atom
is the textual value of Status converted to lower case,
This atom is returned for a NIL/NULL value. Note that if
the reply is only
nil, redis/3 fails. The
may be embedded inside lists or maps.
- A number
Returned if the server replies an integer (":Int"), double
(",Num") or big integer ("(Num")
- A string
Returned on a bulk reply. Bulk replies are supposed to be
in UTF-8 encoding. The the bulk reply starts with
"\u0000T\u0000" it is supposed to be a Prolog term.
Note that this intepretation means it is not possible
to read arbitrary binary blobs.
- A list of replies. A list may also contain
nil. If Reply
as a whole would be
nil the call fails.
- A list of pairs. This is returned for the redis version 3
protocol "%Map". Both the key and value respect the same
rules as above.
Redis bulk replies are translated depending on the
as Type as
- Create a SWI-Prolog string object interpreting the blob as
following Encoding. Encoding is a restricted set of SWI-Prolog's
current locale translation).
- As above, producing an atom.
- As above, producing a list of integers (Unicode code points)
- As above, producing a list of one-character atoms.
- Interpret the bytes as a string representing a number. If
the string does not represent a number of the requested type
type_error(Type, String) is raised.
- Same as integer, but demands the value to be between the Prolog
the value to be used as a dict key.
- Same as
- auto(AsText, AsNumber)
- If the bulk string confirms the syntax of AsNumber, convert
the value to the requested numberical type. Else convert
the value to text according to AsText. This is similar to
the Prolog predicate name/2.
- Alias for
auto(atom,tagged_integer). This allows the value
to be used as a key for a SWI-Prolog dict.
- pairs(AsKey, AsValue)
- Convert a map or array of even length into pairs for which the
key satisfies AsKey and the value AsValue. The
can also be applied to a Redis array. In this case the array
length must be even. This notably allows fetching a Redis
hash as pairs using
HGETALL using version 2 of the
- dict(AsKey, AsValue)
- Similar to
pairs(AsKey, AsValue), but convert the resulting
pair list into a SWI-Prolog dict. AsKey must convert to a
valid dict key, i.e., an atom or tagged integer. See
- Shorthand for
Here are some simple examples
?- redis(default, set(a, 42), X).
X = status("OK").
?- redis(default, get(a), X).
X = "42".
?- redis(default, get(a), X as integer).
X = 42.
?- redis(default, get(a), X as float).
X = 42.0.
?- redis(default, set(swipl:version, 8)).
?- redis(default, incr(swipl:version), X).
X = 9.
- redis_pipeline(+Redis, +PipeLine)[private]
- recover(+Error, +Redis, :Goal)[private]
- Error happened while running Goal on Redis. If this is a recoverable
error (i.e., a network or disconnected peer), wait a little and try
running Goal again.
- wait(+Redis, +Error)[private]
- Wait for some time after a failure. First we wait for 10ms. This is
doubled on each failure upto the setting
max_retry_wait. If the
max_retry_count is exceeded we fail and the called signals
- Connect to the default redis server, call redist/3 using Request,
disconnect and print the result. This predicate is intended for
- redis_write(+Redis, +Command) is det
- redis_read(+Redis, -Reply) is det
- Write command and read replies from a Redis server. These are
building blocks for subscribing to event streams.
- redis_get_list(+Redis, +Key, -List) is det
- redis_get_list(+Redis, +Key, +ChunkSize, -List) is det
- Get the content of a Redis list in List. If ChunkSize is given and
smaller than the list length, List is returned as a lazy list. The
actual values are requested using redis
LRANGE requests. Note
that this results in O(N^2) complexity. Using a lazy list is most
useful for relatively short lists holding possibly large items.
Note that values retrieved are strings, unless the value was added
Term as prolog.
- See also
- - lazy_list/2 for a discussion on the difference between lazy
lists and normal lists.
- redis_set_list(+Redis, +Key, +List) is det
- Associate a Redis key with a list. As Redis has no concept of an
empty list, if List is
, Key is deleted. Note that key values
are always strings in Redis. The same conversion rules as for
- redis_get_hash(+Redis, +Key, -Data:dict) is det
- redis_set_hash(+Redis, +Key, +Data:dict) is det
- Put/get a Redis hash as a Prolog dict. Putting a dict first deletes
Key. Note that in many cases applications will manage Redis hashes
by key. redis_get_hash/3 is notably a user friendly alternative to
HGETALL command. If the Redis hash is not used by
other (non-Prolog) applications one may also consider using the
Term as prolog syntax to store the Prolog dict as-is.
- redis_array_dict(?Array, ?Tag, ?Dict) is det
- Translate a Redis reply representing hash data into a SWI-Prolog
dict. Array is either a list of alternating keys and values or a
list of pairs. When translating to an array, this is always a list
of alternating keys and values.
|Tag||- is the SWI-Prolog dict tag.|
- redis_scan(+Redis, -LazyList, +Options) is det
- redis_sscan(+Redis, +Set, -LazyList, +Options) is det
- redis_hscan(+Redis, +Hash, -LazyList, +Options) is det
- redis_zscan(+Redis, +Set, -LazyList, +Options) is det
- Map the Redis
HSCAN and ZSCAN` commands
into a lazy list. For redis_scan/3 and redis_sscan/4 the result is
a list of strings. For redis_hscan/4 and redis_zscan/4, the result
is a list of pairs. Options processed:
- Adds the
MATCH subcommand, only returning matches for
- Adds the
COUNT subcommand, giving a hint to the size of the
- Adds the
TYPE subcommand, only returning answers of the
- See also
- - lazy_list/2.
- redis_current_command(+Redis, ?Command) is nondet
- redis_current_command(+Redis, ?Command, -Properties) is nondet
- True when Command has Properties. Fails if Command is not defined.
The redis_current_command/3 version returns the command argument
specification. See Redis documentation for an explanation.
- redis_property(+Redis, ?Property) is nondet
- True if Property is a property of the Redis server. Currently uses
redis(info, String) and parses the result. As this is for machine
usage, properties names *_human are skipped.
- redis_subscribe(+Redis, +Channels, -Id, +Options) is det
- Subscribe to one or more Redis PUB/SUB channels. This predicate
creates a thread using thread_create/3 with the given Options. Once
running, the thread listens for messages. The message content is a
string or Prolog term as described in redis/3. On receiving a
message, the following message is broadcasted:
redis(Id, Channel, Data)
If redis_unsubscribe/2 removes the last subscription, the thread
To simply print the incomming messages use e.g.
?- listen(redis(_, Channel, Data),
format('Channel ~p got ~p~n', [Channel,Data])).
?- redis_subscribe(default, test, Id, ).
Id = redis_pubsub_3,
?- redis(publish(test, "Hello world")).
Channel test got "Hello world"
|Id||- is the thread identifier of the listening thread. Note that
the Options |
alias(Name) can be used to get a system wide name.
- redis_subscribe(+Id, +Channels) is det
- redis_unsubscribe(+Id, +Channels) is det
- Add/remove channels from for the subscription. If no subscriptions
remain, the listening thread terminates.
|Channels||- is either a single channel or a list thereof. Each
channel specification is either an atom or a term `A:B:...`, where
all parts are atoms.|
- redis_current_subscription(?Id, ?Channels)
- True when a PUB/SUB subscription with Id is listening on Channels.
- redis_read_stream(+Redis, +Stream, -Term) is det[private]
- Read a message from a Redis stream. Term is one of
- A list of terms (array)
- A list of pairs (map, RESP3 only)
- The atom
- A number
- A term
- A string
- A boolean (
false). RESP3 only.
If something goes wrong, the connection is closed and an exception
- resync(+Redis) is det[private]
- Re-synchronize after an error. This may happen if some type
conversion fails and we have read a partial reply. It is hard to
figure out what to read from where we are, so we echo a random magic
sequence and read until we find the reply.
- redis_read_msg(+Stream, -Message, -Error, -PushMessages) is det[private]
- redis_write_msg(+Stream, +Message) is det[private]
- Read/write a Redis message. Both these predicates are in the foreign
|PushMessages||- is a list of push messages that may be non- if
protocol version 3 (see redis_connect/3) is selected. Using protocol
version 2 this list is always empty.|
The following predicates are exported, but not or incorrectly documented.
- redis_zscan(Arg1, Arg2, Arg3, Arg4)
- redis_hscan(Arg1, Arg2, Arg3, Arg4)
- redis_unsubscribe(Arg1, Arg2)
- redis_read(Arg1, Arg2)
- redis_current_command(Arg1, Arg2, Arg3)
- redis_get_list(Arg1, Arg2, Arg3, Arg4)
- redis_set_hash(Arg1, Arg2, Arg3)
- redis_disconnect(Arg1, Arg2)
- redis_sscan(Arg1, Arg2, Arg3, Arg4)
- redis_connect(Arg1, Arg2, Arg3)