Shulou(Shulou.com)06/01 Report--

I. brief introduction

HBase is a distributed storage system based on column storage and built on HDFS. Its main function is to store massive structured data.

HBase is built on top of HDFS, so HBase also improves the running and storage capacity of the system by adding cheap PCs.

Tables stored in HBase have the following characteristics:

1. Large table: a table can have billions of rows and millions of columns

2. Schemaless: each row has a sortable primary key and any number of columns, which can be dynamically increased as needed, and different rows in the same table can have completely different columns.

3. Column-oriented: column-oriented storage and permission control, column (family) independent retrieval

4. Sparse: for null columns, it does not take up storage space, and tables can be designed to be very sparse.

5. Multiple versions of data: there can be multiple versions of the data in each cell. By default, the version number is automatically assigned, which is the timestamp when the cell is inserted.

6. Single data type: all the data in Hbase are strings, and there is no type.

II. Applicable scenarios of hbase

1. There is high concurrency of read and write.

2. The column families of table structures often need to be adjusted.

3. Store structured or semi-structured data

4. Highly concurrent key-value storage

5. Key random write and orderly storage

6. Save multiple versions of a fixed-size collection for each key

Similarly, there are also scenarios where hbase data are not applicable.

1. Because hbase can only provide row locks, it does not support distributed transactions well.

2. The performance of join and group by in query operation is very poor

3. If the query does not use row-key query, the performance will be very poor, because the full table scan will be performed at this time, and the establishment of a secondary index or multi-level index requires maintaining an index table at the same time.

4. Limited support for random reads with high concurrency

III. Basic structure and component description of hbase

As can be seen from the above figure, hbase includes Clinet, HMaster, HRegionServer and ZooKeeper components.

Introduction to the functions of each component:

1 、 Client

Client communicates with Hbaser and HRegionServer mainly through ZooKeeper. For management operations: client initiates requests to master, for data read and write operations: client initiates requests to regionserver.

2 、 ZooKeeper

Zk is responsible for storing the address of the _ root_ table and the master address of the current service. Regsion server will also register its own information in zk so that master can perceive the state of region server, and zk will coordinate active master, that is, it can provide an election master leader and coordinate the disaster recovery process of each region server.

3 、 HMaster

Master can start multiple master,master, mainly responsible for the management of table and region, respond to users' CRUD operation on the table, manage the load balance of region server, adjust the distribution and distribution of region, and be responsible for migrating the failed regionn when the region server is down.

4 、 HRegionServer

Region server is mainly responsible for responding to users'IO requests and converting IO requests into reading and writing HDFS operations.

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