Hadoop

HDFS

HDFS use inode structrue similar to ext4. Directory entries are sorted inside a directory inode. Refer to: FSNamesystem, FSDirectory, and INodeDirectory. In 0.20.2, rootdir is used as lock. In 3.0.0, ReentrantReadWriteLock is used.

dfs.datanode.sync.behind.writes

• Classes: BlockReceiver.(receivePacket) PacketReceiver.receiveNextPacket
• https://issues.apache.org/jira/browse/HDFS-2465
• Flush after every packet is received not after the write operation is finished.

javadoc

To generte all javadocs for all classes:

• Edit hadoop-project-dist/pom.xml
  • Comment out <doclet>org.apache.hadoop.classification.tools.ExcludePrivateAnnotationsStandardDoclet</doclet>
  • Add <show>package<show>
• mvn javadoc:javadoc

MapR

MapR Architecture Guide

MapR FS

Distributed metadata management. Container: directories, files and blocks. Volumes: group of containers.

HBase

Not
client --> table --> file
But
client --> file