Chapter 3.4 --- HBase.ipynb

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    "## Mission statement\n",
    "\n",
    "* HBase is a wide-column database (for more on what these are look at the Cassandra notes).\n",
    "* However, whilst Cassandra emphasizes availability, HBase emphasizes consistency.\n",
    "* HBase is based on HDFS as the underlying data store. HDFS is designed to be highly durable.\n",
    "* HBase provides good high-volume, large-data, random read-write performance.\n",
    "* Its primary use case is \"reporting\".\n",
    "\n",
    "\n",
    "## Zookeeper\n",
    "* HBase makes use of another Apache project, Zookeeper.\n",
    "* Zookeeper is a high availability, strongly consistent, totally ordered log-based key-value store.\n",
    "* It stores the configuration details for HBase in a durable way, and is meant to be a reusable component that can be plugged into other database architectures.\n",
    "* Zookeeper is designed to address a need common to every database implementation, which is providing configuration details in a durabile way.\n",
    "\n",
    "\n",
    "## Data model and architecture\n",
    "* The HBase server is sharded into a master service and slave daemons.\n",
    "* All of the coordination services live on the master. All of the data lives on the slaves.\n",
    "* There are many services in play; the architecture is relatively complex.\n",
    "* HBase has the concept of a column family. A column family is a set of commonly group-accessed columns which are grouped together in memory. This improves read performance.\n",
    "* HBase also supports having multiple versions of a dataset entry.\n",
    "\n",
    "\n",
    "* Writes are slow (why?).\n",
    "* Reads are fast! HBase is the data store of choice for large Hadoop jobs. Hadoop is the job framework specifically designed for running jobs against data at scale!"
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