elasticsearch 2.2+ index.codec: best_compression启用压缩

官方说法，来自https://www.elastic.co/guide/en/elasticsearch/reference/2.2/index-modules.html#_static_index_settings：

index.codecThe default value compresses stored data with LZ4 compression, but this can be set tobest_compression which uses DEFLATE for a higher compression ratio, at the expense of slower stored fields performance.

注意：2.1以下都是实验特性！2.2+才稳定！

Now you can also enable better compression on the cold nodes by setting index.codec: best_compression in theirconfig/elasticsearch.yml file in order to be able to archive more data with the same amount of disk space.

摘自：https://www.elastic.co/blog/store-compression-in-lucene-and-elasticsearch

下面的数据摘自：https://www.elastic.co/blog/elasticsearch-storage-the-true-story-2.0

The test methodology hasn’t changed so you can check out the old blog post or the README in the Github repo for the details.

Test	String fields	_all	index size /w LZ4	index size /w DEFLATE	expansion ratio /w LZ4	expansion ratio /w DEFLATE	Impact of DEFLATE
Structured data file. Original file size: 67644119
1	analyzed and not_analyzed	enabled	63047579	53131592	0.932	0.785	-0.157
2	analyzed and not_analyzed	disabled	48271433	38327106	0.713	0.566	-0.206
3	not_analyzed	disabled	38920800	29014796	0.575	0.428	-0.254
3b	not_analyzed, except for 'message' field which is retained and analyzed	disabled	65382872	49532858	0.966	0.732	-0.242
4	not_analyzed, except for 'agent' field which is analyzed	disabled	43083702	32063602	0.636	0.474	-0.255
Semi-structured data file. Original file size: 75037027
1	analyzed and not_analyzed	enabled	100478376	82132782	1.339	1.094	-0.182
2	analyzed and not_analyzed	disabled	75238480	56911638	1.002	0.758	-0.243
3	not_analyzed	disabled	71866672	53553561	0.957	0.713	-0.254
3b	not_analyzed, except for 'message' field which is retained and analyzed	disabled	104638750	83824398	1.394	1.117	-0.198
4	not_analyzed, except for 'agent' field which is analyzed	disabled	72925624	54603882	0.971	0.727	-0.251

With the standard LZ4-based compression, the indexed data size to raw data size ratio ranged from 0.575 to 1.394. After enabling DEFLATE-based compression using the best_compression index.codec option, the indexed data size to raw data size ratio range came down to 0.429 to 1.117. Enabling the best_compression option resulted in a 15.7% to 25.6% reduction in indexed data size depending on the test parameters.

As you can see, the ratio of index size to raw data size can vary greatly based on your mapping configuration, what fields you decide to create/retain, and the characteristics of the data set itself. We encourage you to run similar tests yourself to determine what the data compression/expansion factor is for your data set and application requirements.

Conclusion

There were many amazing features added to Elasticsearch 2.0 worth considering. As we’ve discussed, two of these new features in particular can reduce the hardware footprint required for an Elasticsearch cluster by 15-25% or more: 1) the addition of a best_compression option and 2) enabling doc_values by default. This allows us to get to compression ratios between 0.429 and 1.117.