https://blog.cndenis.com/tags/ets.htmlRecent content in Ets on cnDenis的笔记Hugo -- gohugo.iozh-cnSun, 08 Jun 2014 00:00:00 +0000https://blog.cndenis.com/Erlang/2014/06/ets_read_write_concurrency.htmlSun, 08 Jun 2014 00:00:00 +0000https://blog.cndenis.com/Erlang/2014/06/ets_read_write_concurrency.html<p>ETS在创建表时, 有 <code>write_concurrency</code> 和 <code>read_concurrency</code> 这两个选项, 可以用以优化ETS的并发性能.</p> <p><code>write_concurrency</code> 默认设置是 <code>false</code>, 当表进行写操作时, 整个表会被锁起来, 直到写完为止. 把这个值设置为 <code>true</code>, 可以优化并发写性能, 表中的不同项可以同时进行读写, 代价是会消耗一些内存, 并且会降低并发读的性能. 但是对于 <code>order_set</code> 类型的表, 目前的Erlang版本下是不受这个选项影响的.</p> <p><code>read_concurrency</code> 默认设置也是 <code>false</code>, 当设置为 <code>true</code>, 并且Erlang运行在多核机器上且开启SMP支持时, 并发读的性能会提升. 代价是读写切换变得更慢.</p> <p>这两个选项是不会对操作的原子性和独立性有影响的, 也就是说这两项设置<strong>只改变性能, 不影响逻辑</strong>.</p> <p>显然, <code>write_concurrency</code> 适用于读少写多的表, <code>read_concurrency</code> 适用于读多写少的表, 以及读写交替少的表 (即读一大堆数据后再写一大堆, 读取操作较少被写入操作打断).</p> <p>这两个选项是可以同时开启的, 但额外的内存消耗会更大.</p> <p>测试一下, 分别对默认, 开启<code>read_concurrency</code>, 开启<code>write_concurrency</code> 这三种设置, 测试 <code>insert</code>, <code>lookup</code>, <code>update_counter</code> 三种操作</p> <pre><code>bench for default ets ets:insert/2 Single Process: 5664151 call per sec, 8388608 times in 1481 ms 1000 Process: 2448296 call per sec, 4096000 times in 1673 ms ets:lookup/2 Single Process: 6096372 call per sec, 8388608 times in 1376 ms 1000 Process: 9481481 call per sec, 16384000 times in 1728 ms ets:update_counter/3 Single Process: 5821379 call per sec, 8388608 times in 1441 ms 1000 Process: 105872 call per sec, 128000 times in 1209 ms bench for read_concurrency ets ets:insert/2 Single Process: 5418997 call per sec, 8388608 times in 1548 ms 1000 Process: 2493000 call per sec, 4096000 times in 1643 ms ets:lookup/2 Single Process: 4981358 call per sec, 8388608 times in 1684 ms 1000 Process: 10944555 call per sec, 16384000 times in 1497 ms ets:update_counter/3 Single Process: 5769331 call per sec, 8388608 times in 1454 ms 1000 Process: 1935727 call per sec, 2048000 times in 1058 ms bench for write_concurrency ets ets:insert/2 Single Process: 4371343 call per sec, 8388608 times in 1919 ms 1000 Process: 2617252 call per sec, 4096000 times in 1565 ms ets:lookup/2 Single Process: 4507580 call per sec, 8388608 times in 1861 ms 1000 Process: 8062992 call per sec, 8192000 times in 1016 ms ets:update_counter/3 Single Process: 4412734 call per sec, 8388608 times in 1901 ms 1000 Process: 1889298 call per sec, 2048000 times in 1084 ms </code></pre> <p>可以看出, 开启并发性能优化的选项, 对于多进程的<code>update_counter</code>的性能有很大帮助.</p>