系统技术非业余研究

即将发布的R14B01要支持ets的压缩，更大程度的提高内存的利用率。
在github上可以看到这个分支，有兴趣的同学可以下载下来看看。

压缩的时候只压缩value, key是不压缩的。 value特别简单类型的eterm也是不压缩的，因为zip压缩需要一定长度的内容，而且压缩本身也要加入一点的overload.

以下是sverker (author)的提交log.

ETS ‘compressed’ option.

The compressed format is using a slighty modified variant of the extern format
(term_to_binary). To not worsen key lookup’s too much, the top tuple itself
and the key element are not compressed. Table objects with only immediate
non-key elements will therefor not gain anything (but actually consume one
extra word for “alloc_size”).

我们来试验下吧：

# erl +ec
Erlang R14B01 (erts-5.8.2) [source][/source][/source] [64-bit] [smp:48:48] [rq:48] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.2  (abort with ^G)
1> ets:all().
[8207,4110,13,file_io_servers,inet_hosts_file_byaddr,
 inet_hosts_file_byname,inet_hosts_byaddr,inet_hosts_byname,
 inet_cache,inet_db,global_pid_ids,global_pid_names,
 global_names_ext,global_names,global_locks,ac_tab]
2> ets:info(8207).
[{compressed,true},
 {memory,92},
 {owner,<0.26.0>},
 {heir,none},
 {name,shell_records},
 {size,0},
 {node,nonode@nohost},
 {named_table,false},
 {type,ordered_set},
 {keypos,1},
 {protection,public}]
3> ets:new(xx, [public, compressed]).
16400
4> ets:info(16400).                  
[{compressed,true},
 {memory,302},
 {owner,<0.32.0>},
 {heir,none},
 {name,xx},
 {size,0},
 {node,nonode@nohost},
 {named_table,false},
 {type,set},
 {keypos,1},
 {protection,public}]

祝大家玩的开心。