https://github.com/mongodb-partners/mongo-rocks/wiki says
By default 50% of RAM.
https://www.percona.com/doc/percona-server-for-mongodb/3.2/mongorocks.html says
30% of physical memory.
I didn’t set the parameter explicitly, and the server logs didn’t tell me the actual value.
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Block Cache Size GB: 0
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Compression: snappy
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] MaxWriteMBPerSec: 1024
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Engine custom option:
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Crash safe counters: 0
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Counters: 0
2017-08-18T03:06:13.603+0000 I STORAGE [main] [RocksDB] Use SingleDelete in index: 0
2017-08-18T03:06:13.613+0000 I ACCESS [main] Initialized External Auth Session
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] MongoDB starting : pid=4117 port=27017 dbpath=/var/lib/mongo 64-bit host=ip-10-1-12-16
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] db version v3.2.15-3.5
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] git version: 3615e6f7425b87278261a9f2d3e52a14ff3c2a46
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] OpenSSL version: OpenSSL 1.0.1k-fips 8 Jan 2015
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] allocator: tcmalloc
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] modules: none
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] build environment:
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] distarch: x86_64
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] target_arch: x86_64
2017-08-18T03:06:13.616+0000 I CONTROL [initandlisten] options: { config: “/etc/mongod.conf”, processManagement: { fork: true, pidFilePath: “/var/run/mongod.pid” }, replication: { replSetName: “ps-rs2” }, storage: { dbPath: “/var/lib/mongo”, engine: “rocksdb”, journal: { enabled: true } }, systemLog: { destination: “file”, logAppend: true, logRotate: “reopen”, path: “/var/log/mongo/mongod.log” } }
What is the right default value for storage.rocksdb.cacheSizeGB? If it is 30% of physical memory, what is the reason for such a low ratio?