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diff --git a/iredis/data/commands/xpending.md b/iredis/data/commands/xpending.md index 7eb48e0..48840aa 100644 --- a/iredis/data/commands/xpending.md +++ b/iredis/data/commands/xpending.md @@ -1,28 +1,30 @@ -Fetching data from a stream via a consumer group, and not acknowledging such -data, has the effect of creating _pending entries_. This is well explained in -the `XREADGROUP` command, and even better in our -[introduction to Redis Streams](/topics/streams-intro). The `XACK` command will -immediately remove the pending entry from the Pending Entries List (PEL) since -once a message is successfully processed, there is no longer need for the -consumer group to track it and to remember the current owner of the message. - -The `XPENDING` command is the interface to inspect the list of pending messages, -and is as thus a very important command in order to observe and understand what -is happening with a streams consumer groups: what clients are active, what -messages are pending to be consumed, or to see if there are idle messages. -Moreover this command, together with `XCLAIM` is used in order to implement -recovering of consumers that are failing for a long time, and as a result -certain messages are not processed: a different consumer can claim the message -and continue. This is better explained in the -[streams intro](/topics/streams-intro) and in the `XCLAIM` command page, and is -not covered here. +Fetching data from a stream via a consumer group, and not acknowledging +such data, has the effect of creating *pending entries*. This is +well explained in the `XREADGROUP` command, and even better in our +[introduction to Redis Streams](/topics/streams-intro). The `XACK` command +will immediately remove the pending entry from the Pending Entries List (PEL) +since once a message is successfully processed, there is no longer need +for the consumer group to track it and to remember the current owner +of the message. + +The `XPENDING` command is the interface to inspect the list of pending +messages, and is as thus a very important command in order to observe +and understand what is happening with a streams consumer groups: what +clients are active, what messages are pending to be consumed, or to see +if there are idle messages. Moreover this command, together with `XCLAIM` +is used in order to implement recovering of consumers that are failing +for a long time, and as a result certain messages are not processed: a +different consumer can claim the message and continue. This is better +explained in the [streams intro](/topics/streams-intro) and in the +`XCLAIM` command page, and is not covered here. ## Summary form of XPENDING -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`. +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 @@ -39,10 +41,10 @@ OK 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: +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 @@ -55,16 +57,16 @@ information: 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. +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. ## Extended form of XPENDING 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: +`XRANGE`, and a non optional *count* argument, to limit the number +of messages returned per call: ``` > XPENDING mystream group55 - + 10 @@ -74,49 +76,48 @@ returned per call: 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: +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. +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). +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: +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. +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. ## Idle time filter -Since version 6.2 it is possible to filter entries by their idle-time, given in -milliseconds (useful for `XCLAIM`ing entries that have not been processed for -some time): +It is also possible to filter pending stream entries by their idle-time, +given in milliseconds (useful for `XCLAIM`ing 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 +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`. ## Exclusive ranges and iterating the PEL @@ -131,10 +132,6 @@ command. @array-reply, specifically: -The command returns data in different format depending on the way it is called, -as previously explained in this page. However the reply is always an array of -items. - -@history - -- `>= 6.2.0`: Added the `IDLE` option and exclusive range intervals. +The command returns data in different format depending on the way it is +called, as previously explained in this page. However the reply is always +an array of items. |