Flink shared state stack overflow. You are expected to call update() to write changes back.
This has these benefits: Better resource utilization. Making statements based on opinion; back them up with references or personal experience. As you said, you can use broadcast to make state globally available. Correctness after recovery only depends on checkpoints. The stateful RichCoFlatMapFunction will set the ValueState for the key of the current element, i. As soon as this is set, the state is broadcasted to all downstream operator 5 tasks. For more information see the savepoint guide. heap. The long answer is that Flink's state abstractions are not simply a Map or a value container which only store some values. To learn more, see our tips on writing great Aug 7, 2019 · I have googled a lot and can not find useful answers, from flink's documentation, for each parallelism there will be a state instance, and also the run method in one instance of CounterSource will not be called from different threads, so what is the point for the below code. map(point -> hashMap. Hence, the state is directly modified when you modify the object. It wouldn't always be meaningful to try to attribute log lines to just one job, but regardless, the answer is no, there's no support for labeling the TM's log lines to indicate which job is involved. No, Flink will not lose any state (keyed or otherwise) when rescaling. Flink needs to know how to serialize the data that is being broadcast; broadcastStateDescriptors is used by DataStream#broadcast for this purpose. Otherwise, after recovery or rescaling you could end up with inconsistencies. Perhaps the following would meet your needs: The problem with this idea is that you'll have a timer storm if all of the timers fire at the same time (e. "global" meaning that the state is shared across all of the windows having the same key. Then aggregate the results in a subsequent operator using just the one original key. Partition 1 consumer task, reads element from stream and set it in broadcast state. Time windows and temporal joins on versioned tables also work in a similar way. Each TM is configured to run with 14GB of RAM. Flink provides two mechanisms that can be used to clear state. getId, 0)) but I don't know if this would work or if it is efficient in any way. private final ReducingStateDescriptor<Long> stateDesc = new ReducingStateDescriptor<>("count", new Sum(), LongSerializer. First of all, it seems You could use the standard KeyedCoProcess function to achieve what You are now doing with union. state. Nov 12, 2018 · If the application uses the InMemoryStateBackend or the FsStateBackend, all local state is stored on the JVM heap of the worker process, i. val s = StreamExecutionEnvironment. java for an example showing how to use this API with state May 13, 2021 · On prometheues when i query for this cluster (i have 4 hosts), I get metrics for single Task Manager for each host. I want to clean it up by adding some TTL to the values. org. 6. api. To learn more, see our tips on writing great Aug 19, 2020 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Please read the Flink documentation on "Data Types & Serialization" for details of the See full list on flink. Then it is thread-safe. To learn more, see our tips on writing great Stack Overflow for Teams Where developers 2020-07-24 16:18:21,083 INFO org. Key Groups are the atomic unit by which Flink can redistribute Keyed State; there are exactly as many Key Groups as the defined maximum parallelism. Feb 14, 2023 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; at org. 2. readCsv(); points. create(backend, MAX_PARALLELISM) . Therefore for any production use-cases Now, it its seems that the following static object "counter" got initialized, serialized and applied in the worker (Flink engine), is it aligned with the above statement? If worker threads falls in different processes/JVM’s, obviously will not be shared. Thanks for your replay. Oct 20, 2022 · 1. But when I submit my job to Flink k8s operator, "Tuple field #8 of type 'List' will be processed as GenericType. org May 2, 2024 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Now I hope to read configuration from the http interface through a source function every 5 minutes with a parallelism of 1, and then distribute it to all task managers or FlatMapFunctions of the Flink doesn't really provide a mechanism for sharing state between jobs. Flink knows nothing about the state’s data structures and sees only the Nov 16, 2016 · The connect operator will then, send all records from streamA and streamB with identical key to the same operator. Oct 29, 2019 · One way to handle this situation involves adding a second field to the key, resulting in a greater number of possible keys and possibly reducing the data skew across the keys. Only carry over the state you want to keep. addSink(new MySink(m)) These params would be serialized to different machines and seems that it could not be shared by different operators. Feb 14, 2024 · I am new flink and want to process List as Tuple like Tuple8<String, String, String, String List<String>,List<String>,List<String>,List<String>> . answered Oct 30, 2019 at 14:30. Look at CountTrigger for an example. Therefore for any production use-cases Nov 17, 2015 · 3) If some operation updates the state and another one accesses it, you can often implement that with iterations and a CoFlatMapFunction (one side is the original input, the other the feedback input). You'll see that it keeps a count of how many elements have been added to the window in. getCheckpointLock. Jan 9, 2021 · The only types of non-keyed state are ListState, UnionState, and BroadcastState, and ListState is probably the type you want to use. StateBackendLoader May 27, 2018 · In case of both MemoryStateBackend and FsStateBackend the state is always kept in TaskManagers memory and thus must fit in there. In a KeyedProcessFunction, or in a ProcessWindowFunction for a keyed window, whenever you access or update state, there is a key implicitly in context. Mar 1, 2018 · In general, the solution I have in mind would look like this: Map<String, T> hashMap = new DataSet<Point> points = env. JM is configured to run with 1GB. Thanks @david-anderson for the helpful answer! Sep 20, 2023 · how to increase max parallelism in any condition in flink? In the first link, is there any update to the answer David that you gave on this thread. Not entirely, but there are a few things that helped: a) switched to the latest Kinesis supported Flink version (1. And jobB throws. keyBy(<key selector>). I don't know what's the right way to achieve it. That's why asked the original question in the first place. Jun 5, 2019 · Flink’s network stack is one of the core components that make up the flink-runtime module and sit at the heart of every Flink job. Oct 13, 2016 · 3. Jan 2, 2019 · In the following example, I want to connect two unkeyed streams. I've rewritten my answer, proposing an alternative that I believe will work. yaml is related to the runtime memory usage of taskmanager. Feb 26, 2020 · 0. HeapKeyedStateBackend - Initializing heap keyed state Nov 21, 2023 · I also set the Managed Memory to 0 since I'm not using RocksDB as state backend, so the intermediate states should be stored on the heap memory. parallelism. window(<window assigner>) . aggregate(new AverageAggregate(), new MyProcessWindowFunction()); the . , if flatMap1(a: TypeA, out: Collector[TypeOut]) is called for a value from streamA, the state is set for the key a. If we don't set the max parallelism, and we change the Dec 1, 2022 · How can I access a state using the same-id across multiple transformers, for example the following stores an Order object via ValueState in OrderMapper class: env. Mar 21, 2019 · 0. May 23, 2018 · 5. The drawback is that the data of the Apr 12, 2022 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. pop on the way out again. State is maintained independently for each distinct key, and the limit to horizontal scaling is the number of distinct keys (the size of the key Sep 28, 2021 · A few options: (1) Use the State Processor API to modify a savepoint. Sep 12, 2021 · * * <p>It can output zero or more elements using the {@link Collector} parameter, query the * current processing/event time, and also query and update the internal {@link * org. g. You are expected to call update() to write changes back. Jan 22, 2021 · This interface is designed to protect you from trying to manipulate state for keys that cannot be accessed within the local instance (since the state is sharded across the cluster, there's no guarantee that state for any other key than the one for the current event is available in that instance). I have debugged my code and find out that the value of the ValueState "maxVal" is in every flatMap step "null". – Apr 8, 2021 · Flink approaches horizontal scaling by independently processing partitions of the data streams. Also update the state based on the kafka reference data update. 1) backends ( FsStateBackend and MemoryStateBackend) that store the application state on the heap of the worker (TaskManager) JVM process and 2) the RocksDBStateBackend that stores the state in RocksDB on disk. Feb 28, 2019 · When I cancel jobA, jobB fails at the same time. What does it mean and how to fix it? Flink Version 1. In general, Flink's design does not allow to read from or write to state of other subtasks of the same or different operators. It connects individual work units (subtasks) from all TaskManagers. Find the task manager to query state. I haven't tried using state TTL with Mar 14, 2024 · I want to fetch the whole reference data using API on startup and store in flink state. , each parallel instance of the operator will do this. fromElements("1", "2"); Nov 10, 2018 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Context. while (isRunning) {. This comes almost for free, thanks to having Apache Flink as the actual runtime. . With: flink_taskamanger_Status_JVM_Memory_Heap_max{instance="<host>"} I'm getting only 1 result ( There are 8TM's running there i promise :) ) Apr 4, 2019 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company May 7, 2021 · I am facing something similar with a stateful Flink app running on AWS Kinesis Data Analtyics. As such, you typically will only want to use broadcast state in situations where you can comfortably store the May 31, 2023 · Each instance of an operator handling broadcast state receives and potentially stores its own copy of that state (and each instance independently checkpoints its broadcast state). getOrDefault(point. I thought I had to specify the directory where Flink creates it's savepoint. flink. If there are multiple sources of broadcast state, the order of processing those broadcast streams in downstream operators is non-deterministic, which could lead to Mar 2, 2021 · Yes, Triggers can be stateful. In both cases, you can monitor the memory consumption using regular JVM Mar 18, 2019 · If the thread pool you mentioned in the question is Flink task running on the Flink TaskManager. However, I heard of users who leveraged this features in an operator to fetch Feb 28, 2024 · The initializeState() function is more commonly used in situations where you might need to handle custom recovery logic or initialize the contents of the state. 42. Flink is a distributed system. List item getRuntimeContext(). To learn more, see our tips on writing great Dec 9, 2016 · The only way in Flink 1. Raw State is state that operators keep in their own data structures. One way to clear state is to explicitly call clear() on the state object (e. keyBy(Order::getId). I found that ColocationGroup maybe close to the solution. David, I tried as per your inputs. During execution each parallel instance of a keyed operator works with the keys for one or more Key Groups. Stream B has an operator associated with it (FlatMap, but could be anything really) which acts Apr 9, 2020 · 0. To learn more, see our tips on writing great Jul 23, 2021 · Flink is designed to not depend on the survival of the local, working state. Also, I want to take advantage of the built-in TTL mechanism provided by Flink instead of writing my own cleaning logics. This works for Flink >= 1. To expire one day's worth of data every day: After bootstrapping the state, you could send yourself a delayed message, set to be delivered one day later. Or use the State Processor API to dump out a list of all of the keys for which there is state, and then use that knowledge to clear it. I have the same requirement to changing the maxParallelism of a deployed flink job on production. However, Flink does support splitting up a large job among a fleet of workers. common. Both are "global" states, opposed to "window" states of windowState. I am aware that I can access a state store using the TriggerContext ctx object that is available to all Triggers. That means, it is working closely with Flink's checkpoint mechanism. , the state backend just holds a reference to the object. Greetings, Stephan. runtime. The only solution I can see would be to construct a single DataSet holding a type that can hold all the data, such as a Tuple or a Map (for each key), and then use that single compound DataSet to bootstrap all of the states. Anyways, in my experiece, with a good processing pipeline design and partitioning your data in the Aug 23, 2020 · return Tuple2. In this article, we'll take an in-depth look at how Flink's state backend works, explore Aug 9, 2018 · However, you can distribute the workload evenly by setting cluster. INSTANCE); Oct 18, 2016 · Only idea I have is to use stateful transformation - I can merge metadata and sensor events in a single stream and use Flink state storage to store metadata (pseudocode): val sensorInput: DataStream[SensorValue] = readEventsFromKafka() val statisMetadata: DataStream[SensorMetadata] = readMetadataFromJson() val result: DataStream[(SensorValue . util. I cannot afford to lose the state and have restore with the last checkpoint in case of any redeployment. Feb 4, 2019 · I have a use-case in which I would like to share state between two Flink operators: Stream A is the main stream, it flows continuously. 2), b) increased the checkpoint interval to 5 minutes, c) cleaned up explicit state. of(accumulator. And since broadcast state is always MapState, a MapStateDescriptor is what is used to work with it. flatMap(new OrderMapper()). But it seems the two streams can't share states correctly. Jan 17, 2019 · Flink 1. s. map(new MyMap(m)) . May 27, 2018 · In case of both MemoryStateBackend and FsStateBackend the state is always kept in TaskManagers memory and thus must fit in there. Oct 12, 2021 · Can I run a Flink statefun application on an existing Flink session cluster? The docs in older statefun versions (2. Aug 6, 2021 · 1. Two things to say here. If you use the RocksDBStateBackend all state accesses are de/serialized and read Jul 11, 2018 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Can flink's state shared in several stream? 3 Jul 31, 2019 · After running some time, the mapstate becomes so big such that it stalls the entire Flink. The current docs say: "The ProcessFunction can be thought of as a FlatMapFunction with access to keyed state and timers", so, based on this statement, it seems that a normal (non-keyed) ProcessFunction can already work with keyed state and timers, as also claimed here: "If you want to access keyed state and timers you have to apply the Feb 18, 2021 · The state is persisted for us by Flink behind the scene though, when we write something like this: . But it seems crooked to me. windowState is separate per each window, even for the same key. So the update () and the value () method doesn't work in my scenario. To learn more, see our tips on writing great Apr 16, 2021 · 2. For example, by default it's set to 256MB, when a job is Oct 21, 2019 · There is a downstream operator with a parallelism of 5 as well. Stream B is just a dataset of enrichment data. withOperator("my_operator", transformMyOperator) . You can find information about the heap usage specifically from the web interface of your job Aug 12, 2020 · In flink it may be. I would have expected the flink code to be able to do NDC. getExecutionEnvironment(); DataStream<String> stream1 = env. numberOfTaskSlots equal to the number of available CPUs per machine, and. In order to trigger a savepoint you have to use the CLI and call bin/flink savepoint :jobId [:targetDirectory] where the targetDirectory is an optional parameter. Dec 27, 2019 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. See ReadRidesAndFaresSnapshot. addSink(sink1()); Now I would like to access the same Order object via a SubOrderMapper class: Feb 25, 2023 · For the operator state, for example, ListState, It uses CheckpointedFunction's snapshotState and initializeState to save state or restore state. foo and if Feb 7, 2024 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Jun 12, 2018 · The cluster is configured to run with a single Jobmanager and 3 Taskmanager on 3 separate VMs. keyBy(<key selector>) . 5. The difference between those two backends is the way they checkpoint data. In the case of the RocksDB state backend, this is a copy created by deserializing the serialized bytes stored on disk. Slot sharing means that more than one sub-task is scheduled into the same slot -- or in other words, those operator instances end up sharing resources. Aug 29, 2016 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. All approaches in the end localize state access and modifications, which is a good pattern to follow, if possible. 0. Nov 13, 2023 · No, broadcast state is still stored in state and will be available via mechanisms such as checkpoints and savepoints, it just will always be restored in-memory as opposed to other forms of state that can be backed by RocksDB on disk. Another possible approach would be to use state time-to-live to manage its lifecycle. To make it work, you may also have to set: taskmanager. All that rescaling does is to keyed state is to redistribute the data by changing the mapping from key groups to task slots. That way the Aug 26, 2020 · 0. This is done deliberately, so that the state can be resharded when rescaling the cluster. . and in the aggregate process function , I flush the list to state, and if I need to save to dataBase I'm clearing the state and save flag in the state to indicate it. To learn more, see our tips on writing great Feb 10, 2016 · In Flink version 1. How can the state be shared across task slots in multiple task managers so that I can connect the actual data stream and reference data stream to do the enrichment? Jan 28, 2019 · A large static stream (originating from some parquet files we have lying around) which we feed into Flink just to get that Dataset into a saved state; We want to connect the two streams in order to get shared state, so that the 1st stream can use the 2nd state for enrichment. For something this simple, I'd use a FlatMap (with parallelism set to 1) that keeps in state the time of the current window and the last event time. Apr 12, 2021 · What you can do in processBroadcastElement is to access/modify/delete the keyed state for all keys, by using applyToKeyedState with a KeyedStateFunction. In total there are about 30 TM's and i thought that I'll get metrics for all of them. In general, if you want to cache/mirror state from an external database in Flink, the most performant approach is to stream the database mutations into Flink -- in other words, turn Flink into a replication endpoint for the database's change data capture (CDC) stream, if the database supports that. If Flink does fail before completing the first checkpoint, then restart the job from the beginning. push on the way into job specific code and NDC. Nov 29, 2022 · sink state to a db, and use an async function to retrieve it amid the job flow; use state func to update/read from external services amid the job flow; store state in a redis table and retrieve it amid the job flow; I think the first should be the more suitable, as other requires extra setup and extend the complexity to other systems. , midnight). MapState is the kind of state (and the only kind of state) that Flink supports for broadcasting. David Anderson. UnionState is very similar to ListState, it just uses a different strategy for redistributing state during rescaling (each parallel instance gets the entire list, instead of being assigned a slice of the list, and Feb 10, 2016 · In Flink version 1. In case of MemoryStateBackend the checkpoint data is sent to JobManager and kept also in memory there. default equal to the the total number of CPUs in the Jul 9, 2021 · Here I declare my statebackend: val backend = new EmbeddedRocksDBStateBackend(true) And here I create my savepoint: Savepoint. addSource(source1()). Flink does come bundled with an available web interface that can be useful for viewing logs, exceptions, and as you might guess - monitoring resource usage. answered Mar 18, 2019 at 9:59. Chris Gerken. addSource(new MySource(m)) . How do we get jobid hex string using job name. One is to rely on the state time-to-live mechanism, and the other is to use timers with a keyed (co)process function. To learn more, see our tips on writing great Triggering a savepoint. This is usually done by computing a key from every event, and partitioning the stream around that key. Under the hood when the user access Flink state through these abstractions Jul 24, 2020 · 0. window(<window assigner>) is indicating to Flink to hold a piece of state for us for each key and time Jul 12, 2024 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. 3 to read all data before starting to process a stream is to consume the data in the open() method of a RichFlatMapFunction, i. getSum(), newL); @Override. write(savepointPath) Also, my flink cluster is configured to use a RocksDB state backend, and all others flink topologies use the Dec 18, 2020 · 2. apache. We are experiencing 2 memory related issues: - When running Taskmanager with 8GB heap allocation, the TM ran out of heap memory and we got heap out of memory exception. After doing a bit of searching I found a much better example here according Dec 27, 2019 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. I have isolated slots by setting a slot sharing group for my job: someStream. I found an interesting thing here: the size of Task Heap configured in flink-conf. val lock = ctx. evenly-spread-out-slots: true in flink-conf. Yes, that's correct. Code：. Provide details and share your research! But avoid … Asking for help, clarification, or responding to other answers. e. To learn more, see our tips on writing great May 8, 2023 · As you mentioned, the HashMapStateBackend state holds all of its objects on the Java heap. , a ValueState object) when you no longer need it for a particular key. Jun 11, 2019 · Keyed State is further organized into so-called Key Groups. Aug 27, 2018 · 1. Partition 2 consumer task, reads element from stream and set it in broadcast state. 2) said it was possible, but that part has been removed from docs in newer versions, so wondered if it is still possible. 1k 4 35 65. Aug 7, 2023 · Flink's state backend provides the mechanism for storing and managing this state efficiently. Feb 3, 2020 · I am trying to create a custom MyCustomCountTrigger() that should be capable of reading from a state store such as MapState<String, Integer> stateStore that maps key to it's MIN_EVENTS parameter. slotSharingGroup("name"); but it does not work. yaml . Dec 22, 2022 · We currently have a flink-based streaming job (the task is composed of complex FlatMapFunctions DAG), and an http interface for fetching configuration. When checkpointed, they only write a sequence of bytes into the checkpoint. I see. This is typically done in an onTimer() callback in a ProcessFunction. Feb 2, 2021 · 1. Otherwise you might easily end up with some slots doing very little work, while others are quite busy. answered Nov 25, 2021 at 10:22. getState calls are equivalent to globalState of a ProcessWindowFunction. While a function is applied for a specific address, no other message for that address would be applied concurrently. public Acc merge(Acc a, Acc b) {. Apr 3, 2020 · The short answer is that Flink's state abstractions are not designed for concurrent accesses and should not be shared between multiple threads. Flink’s runtime encodes the states and writes them into the checkpoints. Flink provides API (/jobs/overview) to get job information. For the most part, throughout Flink the state for different keys is isolated. 15. Jul 14, 2020 · Yes, StateFun functions would be invoked sequentially per address. A Flink cluster is able to run a single job in parallel, using the resources of one or many multi-core CPUs. In both cases, you can monitor the memory consumption using regular JVM May 30, 2022 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Updated original question with my comments. In fact, you can query any task manager. The queryable state features is intended for external user queries. But if falling to same JVM will "counter" be shared ? private static AtomicLong counter Apr 15, 2024 · You use value() to read the state for the current key. , you have to manually read and parse the file. Whenever a record arrives, if it's in a new hourly window, I'd emit the end_timestamp (last event time), the start_timestamp (from the new record), and update the saved state's current hour. 1. To learn more, see our tips on writing great Dec 18, 2020 · 2. final StreamExecutionEnvironment env = StreamExecutionEnvironment. BroadcastState broadcast state}. However, you must take care to behave deterministically across all parallel instances. Jul 18, 2021 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. It's big (several GBs) and so will not fit in as a broadcast stream. Because the task manager will help you route the key to the correct task manager through a lookupTable from job manager. It won't really differ much but You can have separate classes for both streams so better type safety and better domain segregation in general. When it arrives, delete the oldest data and send another delayed message. UnionState is very similar to ListState, it just uses a different strategy for redistributing state during rescaling (each parallel instance gets the entire list, instead of being assigned a slice of the list, and Jun 12, 2018 · Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. This is basically a broadcast join strategy, i. 9. I have no experience with hbase, but https Oct 23, 2017 · I use a RichFlatMapFunction for this and ValueState to save the current maximum of the appearance of a single hashtag, but this doesn't work. 0, there are two types of state backends. For the operator state, for example, ListState, It uses CheckpointedFunction's snapshotState and initializeState to save state or restore state. The reason Flink SQL has the notion of time attributes is so that suitable streaming queries can have their state automatically cleaned up, and an interval join is an example of such a query. Yes, if that data hasn't been modified since it was loaded, it will all be deleted after one day. It executes the task with parallel operator instances, so the managed state of each operator instance is thread-safe naturally. You may want to define your state within the open() function which is generally used for initial operator configuration similar to the following: Apr 25, 2022 · Here are the two graphs for state size and checkpoint size: State Live Size Checkpoint Size. getExecutionEnvironment. filter(). To learn more, see our tips on writing great Jun 20, 2020 · 5. I think that Flink only supports state on operators and state on Keyed streams, if you need some kind of global state, you have to store and recover data into some kind of database/file system/shared memory and mix that data with your stream. To learn more, see our tips on writing great Jan 23, 2019 · 2. Can we lock the state access/update for sequential access ? Sep 2, 2020 · Thanks David! Still not 100% clear to me, though. Why does the state keep growing and is not bounded by the number of keys in the inout stream? Update: Here's the same two metrics with aligned checkpoints Checkpoint Size State Live Size Nov 25, 2021 · 1. FlinkException: Releasing shared slot parent. Nov 30, 2019 · Examples are “ValueState”, “ListState”, etc. srirzrlggbizcfkbtnhm