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 :
- 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.