原文地址: https://blog.cndenis.com/erlang/2014/06/ets_read_write_concurrency.html
ETS在创建表时, 有 write_concurrency 和 read_concurrency 这两个选项,
可以用以优化ETS的并发性能.
write_concurrency 默认设置是 false, 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 true, 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 order_set 类型的表, 目前的Erlang版本下是不受这个选项影响的.
read_concurrency 默认设置也是 false, 当设置为 true,
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.
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只改变性能, 不影响逻辑.
显然, write_concurrency 适用于读少写多的表,
read_concurrency 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).
这两个选项是可以同时开启的, 但额外的内存消耗会更大.
测试一下, 分别对默认, 开启read_concurrency, 开启write_concurrency 这三种设置,
测试 insert, lookup, update_counter 三种操作
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
可以看出, 开启并发性能优化的选项, 对于多进程的update_counter的性能有很大帮助.
原文地址: https://blog.cndenis.com/erlang/2014/06/ets_read_write_concurrency.html