State statements are an important part of the Flink platform and allow developers to efficiently manage the state of data in streaming applications. They allow you to save and update intermediate results, as well as maintain state during failures and scaling.
The main goal of state operators is to reduce memory and state storage costs. To do this, Flink offers several types of state operators, each with their own features and benefits. Vivekkumar Muthukrishnan, an expert in Data Science and Data Engineering, will explain us how to use them effectively.
According to Vivekkumar it is important to understand the basic types of state operators. One of the most common types of state operators are key operators. They allow you to group data by key and maintain state for each unique key. This is especially useful in the case of data aggregation, when you want to calculate a sum, average, or other statistical information for each key. Keyed operators reduce memory footprint because state is stored only for unique keys, not for each data record. Another type of state operators are window operators. They allow you to group data by time intervals or other conditions. For example, you can create a window for every minute or for every 1000 records. Window operators allow you to handle data flow efficiently, since state is stored only for active windows, not for all data. In addition, Flink offers list state operators that allow you to store a list of values for each key or window. This is especially useful when you want to keep track of multiple values for each key or window, for example, to compute top-N items.
Vivekkumar also gives details on optimising the use of operators. One way to reduce the amount of memory consumed by Flink’s state operators is to use different types of states depending on their size. For example, for small states, you can use In-Memory State Backends, which store data in RAM and provide fast access to it. At the same time, for large states, you can use on-disk states to reduce RAM consumption. You can also apply data compression before writing it to disc to reduce its size. Another optimisation strategy is to use splitting the state into multiple parts. Instead of storing a large state in a single statement, it can be divided into several smaller states, each of which will be processed separately. This allows you to distribute the load among Flink operators and improve parallelism. It is also important to properly manage state during data processing. For example, you can delete unused states or compress them to free up memory. Serialisation and deserialisation mechanisms can also be used to reduce the amount of data transferred while preserving state between iterations. In addition, a useful tool for optimising the use of Flink state operators is to monitor and analyse memory usage. This allows you to identify problematic code sections where memory consumption occurs and make necessary changes to improve it.
The first Vivekkumar’s example of effective use of operators for memory reduction is the use of the ReducingState operator. This operator allows us to aggregate values in a state and reduces the amount of memory needed to store intermediate results. For example, if we have a data stream containing millions of records and we want to find the sum of all the numbers in that stream, then instead of storing all the numbers, we should use the in-memory reduction operator, which will only store the current sum. The second example is the use of the convolution operator (FoldingState). The folding operator allows us to apply a given function to the values in the state and store the results. For example, if we have a data stream containing information about purchases in an online shop and we want to get the total amount of purchases for each user, we can use a folding operator that will add up the purchase amounts for each user. The third example is the use of the list operator (ListState). The list operator allows us to store a set of values in a state. For example, if we have a data stream containing order information for a restaurant and we want a list of all orders for each table, we can use a list operator that will store all orders for each table.
Summarising Vivekkumar gives several recommendations. According to him optimising Flink state operators is an important step to achieve efficiency in resource usage. If the recommendations are implemented, memory reduction and cost minimisation in data processing can be achieved. To reiterate the main points:
1. Using state compression: One way to reduce memory footprint is to use state compression. Flink provides inbuilt compression algorithms such as Gzip and Snappy. It is recommended to use these algorithms to compress state in statements, especially if the state contains a large number of repeated values.
2. Using TTL (Time-To-Live): TTL allows you to automatically delete a state that has become irrelevant. This can be useful if the state is rarely used or if it has a limited lifetime. It is recommended to use TTL to reduce memory footprint, especially if statements contain a large amount of state.
3. Minimising state: It is important to minimise the amount of state that an operator stores. This can be done by analysing the state usage and removing unnecessary states. It is recommended to periodically analyse the state and clear unused or obsolete states.
4. Using RocksDBStateBackend: Flink supports RocksDBStateBackend, which provides efficient state storage on disc. This can significantly reduce memory consumption, especially for operators with large amounts of state. It is recommended to use RocksDBStateBackend for operators with large state volumes.
5. Distributed state: If possible, it is recommended to distribute state across multiple operators or nodes. This distributes the state load and reduces memory consumption on each operator. It is important to consider the relationship between performance and memory consumption when deciding how to distribute state.
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