[GitHub] [bookkeeper] Myasuka commented on a change in pull request #2822: Correct the comment of caching index & filter block with additional options to improve performance

[GitBox <gi...@apache.org>]

Myasuka commented on a change in pull request #2822:
URL: https://github.com/apache/bookkeeper/pull/2822#discussion_r728599774



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File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/storage/ldb/KeyValueStorageRocksDB.java
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@@ -149,8 +149,12 @@ public KeyValueStorageRocksDB(String basePath, String subPath, DbConfigType dbCo
                     tableOptions.setFilterPolicy(new BloomFilter(bloomFilterBitsPerKey, false));
                 }
 
-                // Options best suited for HDDs
+                // Cache index & filter in block cache to limit the memory usage
                 tableOptions.setCacheIndexAndFilterBlocks(true);
+                // Options below are tune to mitigate the performance regression when limiting the memory usage
+                tableOptions.setCacheIndexAndFilterBlocksWithHighPriority(true);

Review comment:
       I think you could refer to [rocksdb-wiki-cache-blocks](https://github.com/facebook/rocksdb/wiki/Block-Cache#caching-index-filter-and-compression-dictionary-blocks) to get some background information of `setCacheIndexAndFilterBlocks`. If this option is set as `false`, table reader would always keep the index & filter block in memory instead of limiting them in a LRU cache. 
   You could also refer to [rocksdb-wiki-cache-blocks](https://github.com/facebook/rocksdb/wiki/Block-Cache#caching-index-filter-and-compression-dictionary-blocks) to see the suggestion to combine these options together.




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