[GitHub] [flink] liyafan82 opened a new pull request #8788: [FLINK-12886][Table SQL / Runtime] Support container memory segment

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liyafan82 opened a new pull request #8788: [FLINK-12886][Table SQL / Runtime] Support container memory segment
URL: https://github.com/apache/flink/pull/8788
 
 
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   ## What is the purpose of the change
   
   We observe that in many scenarios, the operations/algorithms are based on an array of MemorySegment. These memory segments form a large, combined, and continuous memory space.
   
   For example, suppose we have an array of n memory segments. Memory addresses from 0 to segment_size - 1 are served by the first memory segment; memory addresses from segment_size to 2 * segment_size - 1 are served by the second memory segment, and so on.
   
   Specific algorithms decide the actual MemorySegment to serve the operation requests. For some rare cases, two or more memory segments serve the requests. There are many operations based on such a paradigm, for example, BinaryString#matchAt, SegmentsUtil#copyToBytes, LongHashPartition#MatchIterator#get, etc.
   
   The problem is that, for memory segment array based operations, large amounts of code is devoted to
   
   1. Computing the memory segment index & offset within the memory segment.
   2. Processing boundary cases. For example, to write an integer, there are only 2 bytes left in the first memory segment, and the remaining 2 bytes must be written to the next memory segment.
   3. Differentiate processing for short/long data. For example, when copying memory data to a byte array. Different methods are implemented for cases when 1) the data fits in a single segment; 2) the data spans multiple segments.
   
   Therefore, there are much duplicated code to achieve above purposes. What is worse, this paradigm significantly increases the amount of code, making the code more difficult to read and maintain. Furthermore, it easily gives rise to bugs which difficult to find and debug.
   
   To address these problems, we propose a new type of memory segment: ContainerMemorySegment. It is based on an array of underlying memory segments with the same size. It extends from the MemorySegment base class, so it provides all the functionalities provided by MemorySegment. In addition, it hides all the details for dealing with specific memory segments, and acts as if it were a big continuous memory region.
   
   
   With this new type of memory segment, many operations/algorithms can be greatly simplified, without affecting performance. This is because,
   
   1. Many checks, boundary processing are already there. We just move them to the new class.
   2. We optimize the implementation of the new class, so the special optimizations (e.g. optimizations for short data) are still preserved.
   
   
   ## Brief change log
   
   *(for example:)*
     - implement the new memory segment (ContainerMemorySegment)
     - provide unit tests in ContainerMemorySegmentTest
   
   ## Verifying this change
   
   This change added tests and can be verified by ContainerMemorySegmentTest:
   
   
   ## Does this pull request potentially affect one of the following parts:
   
     - Dependencies (does it add or upgrade a dependency): (yes)
     - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (no)
     - The serializers: (no)
     - The runtime per-record code paths (performance sensitive): (yes)
     - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
     - The S3 file system connector: (no)
   
   ## Documentation
   
     - Does this pull request introduce a new feature? (yes)
     - If yes, how is the feature documented? (JavaDocs)
   

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