[jira] [Created] (FLINK-6761) Limitation for maximum state size per key in RocksDB backend

["Stefan Richter (JIRA)" <ji...@apache.org>]

Stefan Richter created FLINK-6761:
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             Summary: Limitation for maximum state size per key in RocksDB backend
                 Key: FLINK-6761
                 URL: https://issues.apache.org/jira/browse/FLINK-6761
             Project: Flink
          Issue Type: Bug
          Components: State Backends, Checkpointing
    Affects Versions: 1.2.1, 1.3.0
            Reporter: Stefan Richter
            Priority: Critical


RocksDB`s JNI bridge allows for putting and getting `byte[]` as keys and values. 
States that internally use RocksDB's merge operator, e.g. `ListState`, can currently merge multiple `byte[]` under one key, which will be internally concatenated to one value in RocksDB. 

This becomes problematic, as soon as the accumulated state size under one key grows larger than `Integer.MAX_VALUE` bytes. Whenever Java code tries to access a state that grew beyond this limit through merging, we will encounter an `ArrayIndexOutOfBoundsException` at best and a segfault at worst.

This behaviour is problematic, because RocksDB silently stores states that exceed this limitation, but on access (e.g. in checkpointing), the code fails unexpectedly.

I think the only proper solution to this is for RocksDB's JNI bridge to build on `(Direct)ByteBuffer` - which can go around the size limitation - as input and output types, instead of simple `byte[]`.



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