XRANGE

XRANGE key start end [COUNT]

Available since

5.0.0

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

@read, @stream, @slow

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.

The 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 SCAN family 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.

- and + special IDs #

The - and + 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 ...

The - and + special IDs mean, respectively, the minimal and maximal range IDs, however they are nicer to type.

Incomplete IDs #

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 to use 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 -0 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.

Exclusive ranges #

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 character (. 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 use 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 previous 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 +.

The command XREAD is also able to iterate the stream. The command XREVRANGE can iterate the stream reverse, from higher IDs (or times) to lower IDs (or times).

Iterating with earlier versions of Redict #

While exclusive range intervals are only available from Redict 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 Redict 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 1526985685299-0.

A symmetrical pattern applies to iterating the stream with XREVRANGE. The 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 XRANGE 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 of XRANGE:

> 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 Redict streams please check our introduction to Redict Streams document.

Examples #

XADD writers * name Virginia surname Woolf
XADD writers * name Jane surname Austen
XADD writers * name Toni surname Morrison
XADD writers * name Agatha surname Christie
XADD writers * name Ngozi surname Adichie
XLEN writers
XRANGE writers - + COUNT 2

History #

6.2.0

Added exclusive ranges.