[GitHub] [flink] Myasuka commented on a change in pull request #10498: [FLINK-14495][docs] Add documentation for memory control of RocksDB state backend

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Myasuka commented on a change in pull request #10498: [FLINK-14495][docs] Add documentation for memory control of RocksDB state backend
URL: https://github.com/apache/flink/pull/10498#discussion_r355905000
 
 

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 File path: docs/ops/state/large_state_tuning.md
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 @@ -210,6 +210,28 @@ and not from the JVM. Any memory you assign to RocksDB will have to be accounted
 of the TaskManagers by the same amount. Not doing that may result in YARN/Mesos/etc terminating the JVM processes for
 allocating more memory than configured.
 
+#### Bound total memory usage of RocksDB instance(s) per slot
+
+RocksDB allocates native memory without control of JVM, and might lead the process to exceed total memory budget of the container to get killed in container environment (e.g. Kubernetes).
+From Flink-1.10, we provide a solution to limit total memory usage for RocksDb instance(s) per slot by leveraging RocksDB's mechanism to 
+share [cache](https://github.com/facebook/rocksdb/wiki/Block-Cache) and [write buffer manager](https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager) among instance(s).
+Generally speaking, we mainly have three parts of memory usage for RocksDB in Flink scenario: block cache, index & bloom filters and memtables 
+(refer to [memory-usage-in-rocksdb](https://github.com/facebook/rocksdb/wiki/Memory-usage-in-RocksDB)).
+The basic idea is to share a `Cache` object with desired capacity among all RocksDB instances, 
+and [cost memory used in memtable to that cache](https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager#cost-memory-used-in-memtable-to-block-cache) via write buffer manager.
+Besides, we also cache index & filters into that cache, then the major use of memory would be well capped.
+There exist two ways to enable this feature:
 
 Review comment:
   Thanks for your suggestion, I will take this description with correctting something not so accurate.

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