HBase 压缩算法设置及修改

Compression就是在用CPU换IO吞吐量/磁盘空间，如果没有什么特殊原因推荐针对Column Family设置compression，下面主要有三种算法: GZIP, LZO, Snappy，作者推荐使用Snappy，因为它有较好的Encoding/Decoding速度和可以接受的压缩率。

HBase comes with support for a number of compression algorithims that can be enabled at the column family level. Enabling compression is recommended unless you have a reason not to do so, for example, when using already compressed content, such as JPEG images. For every other use-case compression usually will yield an overall better performance, because the overhead of the CPU performing the compression and decompression is less than what is required to read more data from disk.

Available Codecs

You can choose from a fixed list of supported compression algorithms. They have different qualities when it comes to compression ratio, as well as CPU and installation requirements.

Table 11.1. Comparison between compression algorithms

Algorithm	% remaining	Encoding	Decoding
GZIP	13.4%	21 MB/s	118 MB/s
LZO	20.5%	135 MB/s	410 MB/s
Zippy/Snappy	22.2%	172 MB/s	409 MB/s

Note that some of the algorithms have a better compression ration while others are faster for the encoding, and a lot faster during decoding. Depending on your use-case you can choose one that suits you best.

Enabling Compression

Enabling compression requires the installation of the JNI and native compression libraries (unless you only want to use the Java code based GZIP compression), as described above, and specifying the chosen algorithm in the column family schema.

One way to accomplish this is during the creation of the table. The possible values are listed in the section called “Column Families”:

 hbase(main):001:0> create 'testtable', { NAME => 'colfam1', COMPRESSION => 'GZ' }
 0 row(s) in 1.1920 seconds

 hbase(main):012:0> describe 'testtable'
 DESCRIPTION                                                 ENABLED
 {NAME => 'testtable', FAMILIES => [{NAME => 'colfam1',      true
 BLOOMFILTER => 'NONE', REPLICATION_SCOPE => '0', VERSIONS
 => '3', COMPRESSION => 'GZ', TTL => '2147483647', BLOCKSIZE
 => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}
 1 row(s) in 0.0400 seconds

The describe shell command is used to read back the schema of the newly created table. You can see the compression is set to GZIP (using the shorter "GZ" value as required). Another option to enable - or change, or disable - the compression algorithm is using the alter command for existing tables:

 hbase(main):013:0> create 'testtable2', 'colfam1'
 0 row(s) in 1.1920 seconds

 hbase(main):014:0> disable 'testtable2'
 0 row(s) in 2.0650 seconds

 hbase(main):016:0> alter 'testtable2', { NAME => 'colfam1', COMPRESSION => 'GZ' }
 0 row(s) in 0.2190 seconds

 hbase(main):017:0> enable 'testtable2'
 0 row(s) in 2.0410 seconds

Note how the table was first disabled. This is necessary to perform the alteration of the column family definition. The final  enable command brings the table back online.