xpending.3valkey - Man Page

When XPENDING is called with just a key name and a consumer group name, it just outputs a summary about the pending messages in a given consumer group. In the following example, we create a consumer group and immediately create a pending message by reading from the group with XREADGROUP.

> XGROUP CREATE mystream group55 0-0
OK

> XREADGROUP GROUP group55 consumer-123 COUNT 1 STREAMS mystream >
1) 1) "mystream"
   2) 1) 1) 1526984818136-0
         2) 1) "duration"
            2) "1532"
            3) "event-id"
            4) "5"
            5) "user-id"
            6) "7782813"

We expect the pending entries list for the consumer group group55 to have a message right now: consumer named consumer-123 fetched the message without acknowledging its processing. The simple XPENDING form will give us this information:

> XPENDING mystream group55
1) (integer) 1
2) 1526984818136-0
3) 1526984818136-0
4) 1) 1) "consumer-123"
      2) "1"

In this form, the command outputs the total number of pending messages for this consumer group, which is one, followed by the smallest and greatest ID among the pending messages, and then list every consumer in the consumer group with at least one pending message, and the number of pending messages it has.

The summary provides a good overview, but sometimes we are interested in the details. In order to see all the pending messages with more associated information we need to also pass a range of IDs, in a similar way we do it with XRANGE, and a non optional count argument, to limit the number of messages returned per call:

> XPENDING mystream group55 - + 10
1) 1) 1526984818136-0
   2) "consumer-123"
   3) (integer) 196415
   4) (integer) 1

In the extended form we no longer see the summary information, instead there is detailed information for each message in the pending entries list. For each message four attributes are returned:

1. The ID of the message.
2. The name of the consumer that fetched the message and has still to acknowledge it. We call it the current owner of the message.
3. The number of milliseconds that elapsed since the last time this message was delivered to this consumer.
4. The number of times this message was delivered.

The deliveries counter, that is the fourth element in the array, is incremented when some other consumer claims the message with XCLAIM, or when the message is delivered again via XREADGROUP, when accessing the history of a consumer in a consumer group (see the XREADGROUP page for more info).

It is possible to pass an additional argument to the command, in order to see the messages having a specific owner:

> XPENDING mystream group55 - + 10 consumer-123

But in the above case the output would be the same, since we have pending messages only for a single consumer. However what is important to keep in mind is that this operation, filtering by a specific consumer, is not inefficient even when there are many pending messages from many consumers: we have a pending entries list data structure both globally, and for every consumer, so we can very efficiently show just messages pending for a single consumer.

It is also possible to filter pending stream entries by their idle-time, given in milliseconds (useful for XCLAIMing entries that have not been processed for some time):

> XPENDING mystream group55 IDLE 9000 - + 10
> XPENDING mystream group55 IDLE 9000 - + 10 consumer-123

The first case will return the first 10 (or less) PEL entries of the entire group that are idle for over 9 seconds, whereas in the second case only those of consumer-123.

The XPENDING command allows iterating over the pending entries just like XRANGE and XREVRANGE allow for the stream’s entries. You can do this by prefixing the ID of the last-read pending entry with the ( character that denotes an open (exclusive) range, and proving it to the subsequent call to the command.