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https://issues.apache.org/jira/browse/ROCKETMQ-317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16279735#comment-16279735
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ASF GitHub Bot commented on ROCKETMQ-317:
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githublaohu commented on issue #195: [ROCKETMQ-317] Take advantage of Linux
native libaio
URL: https://github.com/apache/rocketmq/pull/195#issuecomment-349550112
@lizhanhui
读取 mmap的数据，有两种情况，
第一种是 读取的数据，被mmap映射到内存空间了，那么从内存读取
第二种是 读取的数据，的内存空间被刷下了。从而从磁盘读，mmap默认是读取4K，
1. netty io线程阻塞是因为 第二种情况造成的。引入linux aio是解决第二种情况，致使netty io线程阻塞，造成响应慢的情况。
但是也屏蔽掉了第一种情况，数据被mmap映射到内存中的读取速度 比linux aio的读取数据块太多了，
2. ，linux aio 不使用内存，mmap会把数据映射到内存中，而使用大量的内存，在某些情况下，会占用大量的内存，而不使用。
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> Make full use of Linux native libaio
> -------------------------------------
>
> Key: ROCKETMQ-317
> URL: https://issues.apache.org/jira/browse/ROCKETMQ-317
> Project: Apache RocketMQ
> Issue Type: Improvement
> Reporter: Zhanhui Li
> Assignee: vongosling
>
> libaio is a library, developed as part of the Linux kernel project. With
> libaio, writes are submitted to the operating system where they are processed
> asynchronously. When the writes have been processed, the operating system
> calls the code back.
> When messages being pulled were reclaimed out of main memory, making use of
> Linux native AIO system calls still allows zero-copy without blocking netty
> IO threads.
> https://activemq.apache.org/artemis/docs/latest/libaio.html
> https://www.ibm.com/developerworks/library/l-async/
> https://access.redhat.com/documentation/en-us/jboss_enterprise_application_platform/5/html/hornetq_user_guide/libaio
> https://stackoverflow.com/questions/8768083/difference-between-posix-aio-and-libaio-on-linux
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