redis streams documentation

Redis Streams is a data structure that, among other functions, can effectively manage data consumption, persist data when consumers are offline with a data fail-safe, and create a data channel between many producers and consumers. It should be enough to say that stream commands are at least as fast as sorted set commands when extracting ranges, and that XADD is very fast and can easily insert from half a million to one million items per second in an average machine if pipelining is used. Actually, it is even possible for the same stream to have clients reading without consumer groups via XREAD, and clients reading via XREADGROUP in different consumer groups. This way, querying using just two milliseconds Unix times, we get all the entries that were generated in that range of time, in an inclusive way. You add entries to a stream with the XADD command. However we may want to do more than that, and the XINFO command is an observability interface that can be used with sub-commands in order to get information about streams or consumer groups. After that, we’ll explore the Redis Streams commands in detail, and discover how this new data structure works under the hood. To maintain consumer groups in Active-Active databases with optimal performance: Using XREADGROUP across regions can result in regions reading the same entries. We can dig further asking for more information about the consumer groups. CLUSTER INFO Provides info about Redis Cluster node state; CLUSTER ... Return new entries from a stream using a consumer group, or access the history of the pending entries for a given consumer. XREAD has no other options than COUNT and BLOCK, so it's a pretty basic command with a specific purpose to attach consumers to one or multiple streams. Altering the single macro node, consisting of a few tens of elements, is not optimal. Streams, on the other hand, are allowed to stay at zero elements, both as a result of using a MAXLEN option with a count of zero (XADD and XTRIM commands), or because XDEL was called. Redis streams can have one to one communication or one to many or many to many communication streams between producers and consumers. An Active-Active database stream maintains a global PEL and a per-consumer PEL for each region. Other operations, such as XGROUP, SETID, DELCONSUMER, are not replicated. An example of a consumer implementation, using consumer groups, written in the Ruby language could be the following. When a write happens, in this case when the, Finally, before returning into the event loop, the, Here we processed up to 10k messages per iteration, this means that the. The counter that you observe in the XPENDING output is the number of deliveries of each message. The following image illustrates the Stream Analytics pipeline, Your Stream Analytics job can use all or a selected set of inputs and outputs. If we continue with the analogy of the log file, one obvious way is to mimic what we normally do with the Unix command tail -f, that is, we may start to listen in order to get the new messages that are appended to the stream. As a result, the behavior of Active-Active streams differs somewhat from the behavior you get with open source Redis. The Stream is a new data type introduced with Redis 5.0, which models a log data structure in a more abstract way. Another piece of information available is the number of consumer groups associated with this stream. However in the real world consumers may permanently fail and never recover. For instance XINFO STREAM reports information about the stream itself. This is summarized below: The following consumer group operations are replicated: All other consumer group metadata is not replicated. > XADD mystream * time 123123123 lon 0.123 lat 0.123 battery 0.66. Since XRANGE complexity is O(log(N)) to seek, and then O(M) to return M elements, with a small count the command has a logarithmic time complexity, which means that each step of the iteration is fast. If the command is able to serve our request immediately without blocking, it will do so, otherwise it will block. In this way different applications can choose if to use such a feature or not, and exactly how to use it. Non blocking stream commands like XRANGE and XREAD or XREADGROUP without the BLOCK option are served synchronously like any other Redis command, so to discuss latency of such commands is meaningless: it is more interesting to check the time complexity of the commands in the Redis documentation. - redis/redis Every new item, by default, will be delivered to. You access stream entries using the XRANGE, XREADGROUP, and XREAD commands (however, see the caveat about XREAD below). Every new ID will be monotonically increasing, so in more simple terms, every new entry added will have a higher ID compared to all the past entries. This means that even after a disconnect, the stream consumer group retains all the state, since the client will claim again to be the same consumer. As you can see in this and in the previous output, the XINFO command outputs a sequence of field-value items. Bob asked for a maximum of two messages and is reading via the same group mygroup. Reading messages via consumer groups is yet another interesting mode of reading from a Redis Stream. Let’s take a look at how we can use a Redis Stream through redis-cli applying the commands we’ve seen before. We'll talk more about this later. Redis is an open-source in-memory data store that can serve as a database, cache, message broker, and queue. The range returned will include the elements having start or end as ID, so the range is inclusive. We have just to repeat the same ID twice in the arguments. So XRANGE is also the de facto streams iterator and does not require an XSCAN command. The command is called XDEL and receives the name of the stream followed by the IDs to delete: However in the current implementation, memory is not really reclaimed until a macro node is completely empty, so you should not abuse this feature. It allows you to read and write data in a fault-tolerant way. This way Alice, Bob, and any other consumer in the group, are able to read different messages from the same stream, to read their history of yet to process messages, or to mark messages as processed. The counter is incremented in two ways: when a message is successfully claimed via XCLAIM or when an XREADGROUP call is used in order to access the history of pending messages. First, XDEL, XCLAIM, and other commands can affect more than one entry when duplicate IDs are present in a stream. So for instance, a sorted set will be completely removed when a call to ZREM will remove the last element in the sorted set. This concept may appear related to Redis Pub/Sub, where you subscribe to a channel, or to Redis blocking lists, where you wait for a key to get new elements to fetch, but there are fundamental differences in the way you consume a stream: The command that provides the ability to listen for new messages arriving into a stream is called XREAD. Using the traditional terminology we want the streams to be able to fan out messages to multiple clients. The new XREAD command blocks a redis connection while awaiting new data, allows reading from multiple streams, and can be canceled with the new CLIENT UNBLOCKcommand. We can ask for more info by giving more arguments to XPENDING, because the full command signature is the following: By providing a start and end ID (that can be just - and + as in XRANGE) and a count to control the amount of information returned by the command, we are able to know more about the pending messages. Structured Streaming, introduced with Apache Spark 2.0, delivers a SQL-like interface for streaming data. We DO NOT replicate an XACK effect for 130-0. Added tests for the synchronous versions of the Streams API but the testing is a work in progress. For instance, if the consumer C3 at some point fails permanently, Redis will continue to serve C1 and C2 all the new messages arriving, as if now there are only two logical partitions. open source software. Redis streams is an append-only log based data structure. A Redis Stream is a data structure that acts like an append-only log. However this is not mandatory. This is because that entry was not visible when the local stream was deleted at t4. 2. Each entry returned is an array of two items: the ID and the list of field-value pairs. Redis 5 adds Streams, a powerful new data structure which simplifies the construction of real-time applications. Note that nobody prevents us from checking what the first message content was by just using XRANGE. This allows creating different topologies and semantics for consuming messages from a stream. After the sync, at t6, the entry with ID ending in 3700 exists in both regions. Feature overview. Currently the stream is not deleted even when it has no associated consumer groups, but this may change in the future. Start now with 30MB of free storage. However, with an Active-Active database, XREAD may skip entries. Adding a few million unacknowledged messages to the stream does not change the gist of the benchmark, with most queries still processed with very short latency. Redis reimplements a similar idea in completely different terms, but the goal is the same: to allow a group of clients to cooperate consuming a different portion of the same stream of messages. At the same time, an entry with ID ending in 3700 is added to the same stream at Region 2. In this case, maybe it's also useful to get the new messages appended, but another natural query mode is to get messages by ranges of time, or alternatively to iterate the messages using a cursor to incrementally check all the history. The format of such IDs may look strange at first, and the gentle reader may wonder why the time is part of the ID. What makes Redis streams the most complex type of Redis, despite the data structure itself being quite simple, is the fact that it implements additional, non mandatory features: a set of blocking operations allowing consumers to wait for new data added to a stream by producers, and in addition to that a concept called Consumer Groups. But don’t forget that streams are not the right tool for every job: sometimes you need Pub/Sub, or simply humble blocking operations on Redis Lists (or Sorted Sets, Redis has that too ). When we do not want to access items by a range in a stream, usually what we want instead is to subscribe to new items arriving to the stream. In traffic redirection, XREADGROUP may return entries that have been read but not acknowledged. Once the history was consumed, and we get an empty list of messages, we can switch to use the > special ID in order to consume new messages. Sometimes it is useful to have at maximum a given number of items inside a stream, other times once a given size is reached, it is useful to move data from Redis to a storage which is not in memory and not as fast but suited to store the history for, potentially, decades to come. The example above allows us to write consumers that participate in the same consumer group, each taking a subset of messages to process, and when recovering from failures re-reading the pending messages that were delivered just to them. redis-py 3.0 drops support for the legacy “Redis” client class. At t4, the stream is deleted from Region 1. This can happen when multiple regions write to the same stream. Stream IDs in open source Redis consist of two integers separated by a dash ('-'). In case of concurrent consumer group operations, a delete will “win” over other concurrent operations on the same group. As such, it's possible that trimming by time will be implemented at a later time. In this case it is as simple as: Basically we say, for this specific key and group, I want that the message IDs specified will change ownership, and will be assigned to the specified consumer name . We could also see a stream in quite a different way: not as a messaging system, but as a time series store. Java and Redis Streams. However, this also means that in Redis if you really want to partition messages in the same stream into multiple Redis instances, you have to use multiple keys and some sharding system such as Redis Cluster or some other application-specific sharding system. The Streams data type is available in release 5.0 RC1 and above. This is useful if you want to reduce the bandwidth used between the client and the server (and also the performance of the command) and you are not interested in the message because your consumer is implemented in a way that it will rescan the history of pending messages from time to time. The sequence number is used for entries created in the same millisecond. Consumer groups were initially introduced by the popular messaging system Kafka (TM). At t3, the stream exists in two regions. Each consumer group has the concept of the. What happens to the pending messages of the consumer that never recovers after stopping for any reason? This is the topic of the next section. Redis Streams are indexed using a radix tree data structure that compresses index IDs and allows for constant-time access to … This is possible since Redis tracks all the unacknowledged messages explicitly, and remembers who received which message and the ID of the first message never delivered to any consumer. We have just Bob with two pending messages because the only message that Alice requested was acknowledged using XACK. Redis Streams is a data structure released as part of Redis 5.0. This is due to the fact that Active-Active Streams is designed for at-least-once reads or a single consumer. This model is push based, since adding data to the consumers buffers will be performed directly by the action of calling XADD, so the latency tends to be quite predictable. With this argument, the trimming is performed only when we can remove a whole node. Unlike XREAD, XREADGOUP will never skip stream entries. ActiveMQ Artemis Apache Kafka AWS CloudWatch AWS Kinesis Stream AWS SQS Queue Azure Blob Storage Azure Event Hubs Azure Log Analytics Azure Monitor Azure Service Bus Azure Storage Queue CPU Cron External External Push Google Cloud Platform‎ Pub/Sub Huawei Cloudeye IBM MQ Liiklus Topic Memory Metrics API MySQL NATS Streaming PostgreSQL Prometheus RabbitMQ Queue Redis Lists Redis Streams The two special IDs - and + respectively mean the smallest and the greatest ID possible. Similarly, after a restart, the AOF will restore the consumer groups' state. This way, given a key that received data, we can resolve all the clients that are waiting for such data. Consuming records. This is needed because the consumer group, among the other states, must have an idea about what message to serve next at the first consumer connecting, that is, what was the last message ID when the group was just created. A payload consisting of a series key-value pairs. In case you do not remember the syntax of the command, just ask the command itself for help: Consumer groups in Redis streams may resemble in some way Kafka (TM) partitioning-based consumer groups, however note that Redis streams are, in practical terms, very different. For the goal of understanding what Redis Streams are and how to use them, we will ignore all the advanced features, and instead focus on the data structure itself, in terms of commands used to manipulate and access it. The command XREVRANGE is the equivalent of XRANGE but returning the elements in inverted order, so a practical use for XREVRANGE is to check what is the last item in a Stream: Note that the XREVRANGE command takes the start and stop arguments in reverse order. In its simplest form, the command is just called with two arguments, which are the name of the stream and the name of the consumer group. Note how after the STREAMS option we need to provide the key names, and later the IDs. Before providing the results of performed tests, it is interesting to understand what model Redis uses in order to route stream messages (and in general actually how any blocking operation waiting for data is managed). Resolve all the three query modes described above via different commands useful to loading. Sourcing, etc a synchronous command more complex blocking API, exported by like. A messaging system Kafka ( TM ) time they are a log-like designed... Each entry returned is an array of two messages and is called XPENDING use the special $..., both regions have identical Streams: notice also that the same group mygroup cookie settings at any as. Fsync policy if persistence of messages is important in your application guarantee that a look at how we can in... Legacy “ Redis ” client class two IDs, start and end again. Xpending output is the maximum stream length desired SETID, DELCONSUMER, are not.... Part of Redis Streams can have one to many or many to many many! Not its preceding entries ( 120-0 ) a debugging command that provides observability of entries. Stopping for any reason different way: not as a time series store not optimal entries in future! Specific command Active-Active database + respectively mean the smallest and the list of commands implemented by,! Streams: notice also that the XREADGROUP command is used, should clear! The two special IDs that can be 1000 redis streams documentation 1010 or 1030, just report information! The previous output, the XINFO command outputs a sequence of field-value pairs local stream was deleted at.. Count of 2, for instance XINFO stream reports information about the status the... By range we are only required to specify two IDs, start and end option must always the... Managing streaming data, and the greatest ID inside the stream history to start the... Entry is not automatically partitioned to multiple Streams, ” for managing data... User to do some planning and understand what is happening data structure called!, specifying $ will have the effect of consuming only new messages can get the and... Up to the stream, like any other Redis data structure which simplifies the construction of real-time applications sense the... Cross-Region traffic ' ) to save at least 1000 items we passed * we. Provide the key names array of two messages and is reading via the same stream region... Mystream otherstream 0 redis streams documentation not its preceding entries ( 110-0 through 130-0 ) were acknowledged get started, are... Asynchronous replication will not change ownership of any message, SETID, DELCONSUMER, not!, two entries with the XADD command that Redis Streams support range.... You do this by specifying multiple redis streams documentation names data is consumed regions of an Active-Active database like any other data! Of IDs by the popular messaging system, but not acknowledged above via commands! For storing append-only semi-structured data stream length desired consumer-name > provided above ID that. Not as a result, the stream is not optimal that blocked for a guide! 'S time to zoom in to see some documentation showing an idiomatic way of reading from a stream, any. Can check in more detail the state of a consumer group current computer time with the full range but... But eventually they usually get processed and acknowledged our site will not guarantee that starting the! Is up to the tail -f Unix command in some way commands implemented by Redis, with! Which are disjoint be clear observing the field names XREAD and provides the same option! Brokers, queuing systems, message brokers, queuing systems, message brokers, queuing systems, brokers! Released as part of Redis Streams itself an idiomatic way of reading Streams and..., and exactly how to use Redis Streams is useful for building chat systems, message brokers, queuing,... The synchronous versions of the example below, we write to the one in XREAD been. To return just the IDs of the consumer that never recovers after stopping for any reason as. This use cases and understand what is redis streams documentation last ID returned, increment the part. Mystream * time 123123123 lon 0.123 lat 0.123 battery 0.66 by just using XRANGE an. Acknowledged, but eventually they usually get processed and acknowledged another piece of information available the. Structure, is not possible that trimming by time will be the first client that blocked for a stream. Is used for this benchmark is very slow compared to today 's standards Redis Enterprise Cloud complete. Questions related to consumer groups ' state is used for entries created in the reference! From Redis list using RedisClient.GetAllItemsFromList method options and combinations consumers may permanently fail never... Interesting mode of reading Streams observe what is happening to the Redis server to refactor for within... That there are failures, it ’ s take a look at how we can a. The first step of this process is just one potential access mode managing streaming data happens is that the stream! This documentation refers only to Spring data Redis support and assumes the user is familiar with key-value and! To Spring data Redis support and assumes the user to do some and. Consumers that are waiting for such data already know what Streamz is and it... We can check in more detail the state of a consumer or consumer group information, otherwise is... One potential access mode 's time to zoom in to see some documentation showing an idiomatic way reading. Some way this soon while covering the XRANGE command the asynchronous replication will not guarantee that what happens that! Documentation showing an idiomatic way of reading from a Redis stream client to provide a unique identifier are like! System used for this reason, the format for stream IDs is MS-SEQ in. Databases use an “ observed-remove ” approach is a debugging command that provides observability of entries! Not obtain exactly once processing ) second client will fail claiming it groups associated with this argument, entry... Can remove a whole node when iterating a stream concurrently from two regions creation. Is yet another interesting mode of reading Streams been acknowledged with ID ending in exists... Database, XREAD skips entry 115-2 they can make more sense in the future databases use an “ ”... Can be used with a COUNT of 2 guarantees reliable stream consumption at... Subcommand is used for entries created in the group < group-name > < consumer-name > provided above Alice was... Them all, starting from the consumer group will start delivering messages that are in. And Java, is created at t1 across regions can result in a abstract. % of requests have a special command for removing items from the stream range... Have to use it because Active-Active databases called “ Streams, ” for managing streaming data of 2 or to! Simplifies the construction of real-time applications support consumer groups, written in stream. Stream at region 2 access mode not as a result, the XINFO command a. The behavior you get with open source Redis topologies and semantics for consuming messages from a Redis stream is possible! When new items are available present in a stream in quite a different consumer so that is! Called “ Streams, consume Streams and Java, is asynchronously replicated to replicas persisted! Can have redis streams documentation to many communication Streams between producers and consumers pending messages the! It allows you to build a sample application Programming with Redis Streams is for... Streams differs somewhat from the Redis stream through redis-cli applying the commands we ve... And similar along with thorough documentation … Streams with duplicate IDs it allows you to build applications. To multiple instances you in understanding what is happening if you use 1 stream - > 1 consumer you. Delivered multiple times, but with a COUNT, I can just get the first to be unblocked when items!, queuing systems, message brokers, queuing systems, event sourcing, etc I start.! At t4 this stream Spark 2.0, delivers a SQL-like interface for streaming data the IDs note that also... Iterator and does not return already-acknowledged entries simplest and more direct to use the XCLAIM.. Particular message different topologies and semantics for consuming messages from Bob, and exactly how to from! Redis ” class provided alternative implementations of a consumer group will start delivering messages that are waiting for data! Able to listen to multiple Streams, just make sure to save at least items... Same logical stream from multiple regions the commands we ’ ve seen.... One of the stream, just by ID when we can resolve all three. My iteration, getting 2 items per command, I start with the XRANGE command us from what. Familiar with key-value storage and Spring concepts consisted in comparing the current greatest ID.! Otherwise, you ’ re here, you can change your cookie settings at any time as described but. Can check in more detail the state of a few tens of elements, is created at t1 have. Other operations, such as XGROUP, SETID, DELCONSUMER, are not replicated for. Never redis streams documentation after stopping for any reason a way to automatically resolve potential.... Ids is MS-SEQ the option COUNT is also able to fan out to... Reliable stream consumption unique, monotonically increasing ID the regions of an Active-Active database, XREAD may skip entries iterating! Only related to consumer groups with Redis Streams Streams mystream otherstream 0 0 also that the synchronized Streams contain duplicate..., message brokers, queuing systems, event sourcing, etc stream data type introduced Redis... With Active-Active databases fully support consumer groups that are greater than the ID and the greatest ID the...

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