redis commands streams xreadgroup

XREADGROUP

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Read with a consumer group

Usage: XREADGROUP GROUP group consumer count 1 STREAMS key id-or->.
The last ID is usually the special ID '>' rather than a specific ID. Each call then returns the next never-delivered entries.

After XREADGROUP you must XACK when processing is complete.

BLOCK option

With BLOCK, if there is no data the command waits up to the given milliseconds.

• XREADGROUP GROUP group consumer count 1 BLOCK 1000 STREAMS key >

XREAD BLOCK uses '$' only on the first call; here you keep using '>'.

Several consumers on one stream

Several consumers can take turns on one stream. If there is a lot of work and processing is slow, assign multiple consumers.

• XREADGROUP GROUP CG-A Consumer-1 count 1 STREAMS sensor-1234  >
  Result: temperature 100
• XREADGROUP GROUP CG-A Consumer-2 count 1 STREAMS sensor-1234  >
  Result: temperature 101
• XREADGROUP GROUP CG-A Consumer-3 count 1 STREAMS sensor-1234  >
  Result: temperature 102

Several streams

You can read from several streams.

• XREADGROUP GROUP CG-A Consumer-1 count 1 STREAMS sensor-1234 sensor-5678  > >

COUNT 1 then reads one entry from each stream.

Syntax

XREADGROUP GROUP group consumer
[COUNT count] [BLOCK milliseconds]
STREAMS key [key ...] ID [ID ...]

• Available since version 5.0.0.
• Time complexity is O(log(N)+M), where N is the number of stream entries and M is the number of entries returned.