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Merge pull request #244 from nats-io/stream-option-doc-change

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JetStream documentation updates
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Ginger Collison 2021-04-26 16:34:52 -05:00 committed by GitHub
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jetstream/concepts/consumers.md
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# Consumers # Consumers
Each Consumer, or related group of Consumers, of a Stream will need an Consumer defined. It's ok to define thousands of these pointing at the same Stream. Each Consumer, or related group of Consumers, of a Stream will need a Consumer defined. It's ok to define thousands of these pointing at the same Stream.
Consumers can either be `push` based where JetStream will deliver the messages as fast as possible to a subject of your choice or `pull` based for typical work queue like behavior. The rate of message delivery in both cases is subject to `ReplayPolicy`. A `ReplayInstant` Consumer will receive all messages as fast as possible while a `ReplayOriginal` Consumer will receive messages at the rate they were received, which is great for replaying production traffic in staging. Consumers can either be `push` based where JetStream will deliver the messages as fast as possible to a subject of your choice or `pull` based to have control by asking the server for messages. The rate of message delivery in both cases is subject to `ReplayPolicy`. A `ReplayInstant` Consumer will receive all messages as fast as possible while a `ReplayOriginal` Consumer will receive messages at the rate they were received, which is great for replaying production traffic in staging.
In the orders example above we have 3 Consumers. The first two select a subset of the messages from the Stream by specifying a specific subject like `ORDERS.processed`. The Stream consumes `ORDERS.*` and this allows you to receive just what you need. The final Consumer receives all messages in a `push` fashion. In the orders example above we have 3 Consumers. The first two select a subset of the messages from the Stream by specifying a specific subject like `ORDERS.processed`. The Stream consumes `ORDERS.*` and this allows you to receive just what you need. The final Consumer receives all messages in a `push` fashion.
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| AckPolicy | How messages should be acknowledged, `AckNone`, `AckAll` or `AckExplicit` | | AckPolicy | How messages should be acknowledged, `AckNone`, `AckAll` or `AckExplicit` |
| AckWait | How long to allow messages to remain un-acknowledged before attempting redelivery | | AckWait | How long to allow messages to remain un-acknowledged before attempting redelivery |
| DeliverPolicy | The initial starting mode of the consumer, `DeliverAll`, `DeliverLast`, `DeliverNew`, `DeliverByStartSequence` or `DeliverByStartTime` | | DeliverPolicy | The initial starting mode of the consumer, `DeliverAll`, `DeliverLast`, `DeliverNew`, `DeliverByStartSequence` or `DeliverByStartTime` |
| DeliverySubject | The subject to deliver observed messages, when not set, a pull-based Consumer is created | | DeliverySubject | The subject to deliver observed messages. Useful to setup an alternate subject for a regular NatsSubcriber can listen on that subject. Not allowed for pull subscriptions. |
| Durable | The name of the Consumer | | Durable | The name of the Consumer, which the server will track, allowing resuming consumption where left off. |
| FilterSubject | When consuming from a Stream with many subjects, or wildcards, select only a specific incoming subjects, supports wildcards | | FilterSubject | When consuming from a Stream with many subjects, or wildcards, select only a specific incoming subjects, supports wildcards |
| MaxDeliver | Maximum amount times a specific message will be delivered. Use this to avoid poison pills crashing all your services forever | | MaxDeliver | Maximum amount times a specific message will be delivered. Use this to avoid poison pills crashing all your services forever |
| OptStartSeq | When first consuming messages from the Stream start at this particular message in the set | | OptStartSeq | When first consuming messages from the Stream start at this particular message in the set |

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jetstream/concepts/streams.md
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Streams define how messages are stored and retention duration. Streams consume normal NATS subjects, any message found on those subjects will be delivered to the defined storage system. You can do a normal publish to the subject for unacknowledged delivery, else if you send a Request to the subject the JetStream server will reply with an acknowledgement that it was stored. Streams define how messages are stored and retention duration. Streams consume normal NATS subjects, any message found on those subjects will be delivered to the defined storage system. You can do a normal publish to the subject for unacknowledged delivery, else if you send a Request to the subject the JetStream server will reply with an acknowledgement that it was stored.
As of January 2020, in the tech preview we have `file` and `memory` based storage systems, we do not yet support clustering. As of January 2020, in the tech preview we have `File` and `Memory` based storage systems, we do not yet support clustering.
In the diagram above we show the concept of storing all `ORDERS.*` in the Stream even though there are many types of order related messages. We'll show how you can selectively consume subsets of messages later. Relatively speaking the Stream is the most resource consuming component so being able to combine related data in this manner is important to consider. In the diagram above we show the concept of storing all `ORDERS.*` in the Stream even though there are many types of order related messages. We'll show how you can selectively consume subsets of messages later. Relatively speaking the Stream is the most resource consuming component so being able to combine related data in this manner is important to consider.
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| Item | Description | | Item | Description |
| :--- | :--- | | :--- | :--- |
| MaxAge | Maximum age of any message in the stream, expressed in microseconds | | Name | A name for the Stream that may not have spaces, tabs, period (`.`), greater than (`>`) or asterix (`*`) |
| MaxBytes | How big the Stream may be, when the combined stream size exceeds this old messages are removed | | Storage | The type of storage backend, `File` and `Memory` |
| MaxMsgSize | The largest message that will be accepted by the Stream | | Subjects | A list of subjects to consume, supports wildcards |
| MaxMsgs | How many messages may be in a Stream, oldest messages will be removed if the Stream exceeds this size |
| MaxConsumers | How many Consumers can be defined for a given Stream, `-1` for unlimited |
| Name | A name for the Stream that may not have spaces, tabs or `.` |
| NoAck | Disables acknowledging messages that are received by the Stream |
| Replicas | How many replicas to keep for each message in a clustered JetStream, maximum 5 | | Replicas | How many replicas to keep for each message in a clustered JetStream, maximum 5 |
| MaxAge | Maximum age of any message in the stream, expressed in nanoseconds. |
| MaxBytes | How many bytes the Stream may contain. Adheres to Discard Policy, removing oldest or refusing new messages if the Stream exceeds this number of messages. |
| MaxMsgs | How many messages may be in a Stream. Adheres to Discard Policy, removing oldest or refusing new messages if the Stream exceeds this size |
| MaxMsgSize | The largest message that will be accepted by the Stream |
| MaxConsumers | How many Consumers can be defined for a given Stream, `-1` for unlimited |
| NoAck | Disables acknowledging messages that are received by the Stream |
| Retention | How message retention is considered, `LimitsPolicy` \(default\), `InterestPolicy` or `WorkQueuePolicy` | | Retention | How message retention is considered, `LimitsPolicy` \(default\), `InterestPolicy` or `WorkQueuePolicy` |
| Discard | When a Stream reached it's limits either, `DiscardNew` refuses new messages while `DiscardOld` \(default\) deletes old messages | | Discard | When a Stream reached it's limits either, `DiscardNew` refuses new messages while `DiscardOld` \(default\) deletes old messages |
| Storage | The type of storage backend, `file` and `memory` as of January 2020 | | Duplicates | The window within which to track duplicate messages, expressed in nanoseconds. |
| Subjects | A list of subjects to consume, supports wildcards |
| Duplicates | The window within which to track duplicate messages |