XRANGE key start end [COUNT count]
- Available since:
- Time complexity:
- O(N) with N being the number of elements being returned. If N is constant (e.g. always asking for the first 10 elements with COUNT), you can consider it O(1).
- ACL categories:
The command returns the stream entries matching a given range of IDs. The range is specified by a minimum and maximum ID. All the entries having an ID between the two specified or exactly one of the two IDs specified (closed interval) are returned.
XRANGE command has a number of applications:
- Returning items in a specific time range. This is possible because Stream IDs are related to time.
- Iterating a stream incrementally, returning just
a few items at every iteration. However it is semantically much more
robust than the
SCANfamily of functions.
- Fetching a single entry from a stream, providing the ID of the entry to fetch two times: as start and end of the query interval.
The command also has a reciprocal command returning items in the
reverse order, called
XREVRANGE, which is otherwise identical.
+ special IDs
+ special IDs mean respectively the minimum ID possible
and the maximum ID possible inside a stream, so the following command
will just return every entry in the stream:
> XRANGE somestream - + 1) 1) 1526985054069-0 2) 1) "duration" 2) "72" 3) "event-id" 4) "9" 5) "user-id" 6) "839248" 2) 1) 1526985069902-0 2) 1) "duration" 2) "415" 3) "event-id" 4) "2" 5) "user-id" 6) "772213" ... other entries here ...
- ID is effectively just exactly as specifying
+ is equivalent to
they are nicer to type.
Stream IDs are composed of two parts, a Unix millisecond time stamp and a
sequence number for entries inserted in the same millisecond. It is possible
XRANGE specifying just the first part of the ID, the millisecond time,
like in the following example:
> XRANGE somestream 1526985054069 1526985055069
In this case,
XRANGE will auto-complete the start interval with
and end interval with
-18446744073709551615, in order to return all the
entries that were generated between a given millisecond and the end of
the other specified millisecond. This also means that repeating the same
millisecond two times, we get all the entries within such millisecond,
because the sequence number range will be from zero to the maximum.
Used in this way
XRANGE works as a range query command to obtain entries
in a specified time. This is very handy in order to access the history
of past events in a stream.
The range is close (inclusive) by default, meaning that the reply can include
entries with IDs matching the query's start and end intervals. It is possible
to specify an open interval (exclusive) by prefixing the ID with the
(. This is useful for iterating the stream, as explained below.
Returning a maximum number of entries
Using the COUNT option it is possible to reduce the number of entries reported. This is a very important feature even if it may look marginal, because it allows, for instance, to model operations such as give me the entry greater or equal to the following:
> XRANGE somestream 1526985054069-0 + COUNT 1 1) 1) 1526985054069-0 2) 1) "duration" 2) "72" 3) "event-id" 4) "9" 5) "user-id" 6) "839248"
In the above case the entry
1526985054069-0 exists, otherwise the server
would have sent us the next one. Using
COUNT is also the base in order to
XRANGE as an iterator.
Iterating a stream
In order to iterate a stream, we can proceed as follows. Let's assume that we want two elements per iteration. We start fetching the first two elements, which is trivial:
> XRANGE writers - + COUNT 2 1) 1) 1526985676425-0 2) 1) "name" 2) "Virginia" 3) "surname" 4) "Woolf" 2) 1) 1526985685298-0 2) 1) "name" 2) "Jane" 3) "surname" 4) "Austen"
Then instead of starting the iteration again from
-, as the start
of the range we use the entry ID of the last entry returned by the
XRANGE call as an exclusive interval.
The ID of the last entry is
1526985685298-0, so we just prefix it
with a '(', and continue our iteration:
> XRANGE writers (1526985685298-0 + COUNT 2 1) 1) 1526985691746-0 2) 1) "name" 2) "Toni" 3) "surname" 4) "Morrison" 2) 1) 1526985712947-0 2) 1) "name" 2) "Agatha" 3) "surname" 4) "Christie"
And so forth. Eventually this will allow to visit all the entries in the
stream. Obviously, we can start the iteration from any ID, or even from
a specific time, by providing a given incomplete start ID. Moreover, we
can limit the iteration to a given ID or time, by providing an end
ID or incomplete ID instead of
Iterating with earlier versions of Redis
While exclusive range intervals are only available from Redis 6.2, it is still possible to use a similar stream iteration pattern with earlier versions. You start fetching from the stream the same way as described above to obtain the first entries.
For the subsequent calls, you'll need to programmatically advance the last
entry's ID returned. Most Redis client should abstract this detail, but the
implementation can also be in the application if needed. In the example above,
this means incrementing the sequence of
1526985685298-0 by one, from 0 to 1.
The second call would, therefore, be:
> XRANGE writers 1526985685298-1 + COUNT 2 1) 1) 1526985691746-0 2) 1) "name" 2) "Toni" ...
Also, note that once the sequence part of the last ID equals
18446744073709551615, you'll need to increment the timestamp and reset the
sequence part to 0. For example, incrementing the ID
1526985685298-18446744073709551615 should result in
A symmetrical pattern applies to iterating the stream with
only difference is that the client needs to decrement the ID for the subsequent
calls. When decrementing an ID with a sequence part of 0, the timestamp needs
to be decremented by 1 and the sequence set to 18446744073709551615.
Fetching single items
If you look for an
XGET command you'll be disappointed because
is effectively the way to go in order to fetch a single entry from a
stream. All you have to do is to specify the ID two times in the arguments
> XRANGE mystream 1526984818136-0 1526984818136-0 1) 1) 1526984818136-0 2) 1) "duration" 2) "1532" 3) "event-id" 4) "5" 5) "user-id" 6) "7782813"
Additional information about streams
For further information about Redis streams please check our introduction to Redis Streams document.
Array reply, specifically:
The command returns the entries with IDs matching the specified range.
The returned entries are complete, that means that the ID and all the fields
they are composed are returned. Moreover, the entries are returned with
their fields and values in the exact same order as
XADD added them.
- Starting with Redis version 6.2.0: Added exclusive ranges.