lMemory access latency issues: ØDirect reclaim • Background reclaim (kswapd) • Foreground reclaim (direct reclaim) ØPage fault • Major page fault will produce latency Memory Access Latency(Page Fault) Fault) alloc mem free mem? No Latency Page Reclaiming back-reclaim No Latency Direct Reclaim Y N Enough NOT Enough Latency lDirect reclaim Øvm.min_free_kbytes: 3g Øvm.extra_free_kbytes: 8g Used add_to_page_cache_locked 自旋锁- treelock 1.4万亿 低延迟分布式存储系统 – PageCache的毛刺内核源码分析 lMemory access latency issues: ØMemory lock ØWake_up_page ØWait_on_page_locked() ØWait_on_page_writebacfk() LOCKED DIRTY

lMemory access latency issues: ØDirect reclaim • Background reclaim (kswapd) • Foreground reclaim (direct reclaim) ØPage fault • Major page fault will produce latency Memory Access Latency(Page Fault) Fault) alloc mem free mem? No Latency Page Reclaiming back-reclaim No Latency Direct Reclaim Y N Enough NOT Enough Latency lDirect reclaim Øvm.min_free_kbytes: 3g Øvm.extra_free_kbytes: 8g Used add_to_page_cache_locked 自旋锁- treelock 1.4万亿 低延迟分布式存储系统 – PageCache的毛刺内核源码分析 lMemory access latency issues: ØMemory lock ØWake_up_page ØWait_on_page_locked() ØWait_on_page_writebacfk() LOCKED DIRTY

.................................................................................. 6 4.7 Low Latency Messaging ...................................................................................... 术可以完全避免单点， 同步双写势必会影响性能，适合对消息可靠性要求极高的场合，例如不 Money 相关的应用。 RocketMQ 从 3.0 版本开始支持同步双写。 4.7 Low Latency Messaging 在消息丌堆积情冴下，消息到达 Broker 后，能立刻到达 Consumer。 RocketMQ 使用长轮询 Pull 方式，可保证消息非常实时，消息实时性丌低亍 Push。

Supported Supported, property filter expressi ns based on SQL92 Supported High performance and low latency file storage upported timestamp and offset two indicates Not Supported Supported, Master-Sl ve