[rabbitmq-discuss] publishing confirms with persistent messages?

[Ernest Staszuk]

In fact it is possible that rabbit sends confirmation and data
is not stored. The fsync does NOT guarantee that data has been
actually written. What it does is a assurance that hard disk
reported completion of data transfer. Due to writing cashe
of hard memory there could exist a time window when
data has not been permanently stored yet. This could be
prevented by disabling hard disk's writing cache.


W dniu 2012-07-20 10:48, Francesco Mazzoli pisze:
> At Fri, 20 Jul 2012 16:33:23 +0800,
> 黄大鹏 wrote:
>> Hi all,
>>     I read this  "Persistent messages are confirmed when all queues have either
>> delivered the message and received an acknowledgement (if required), or
>> persisted the message." on the offical blog. but when i read the source code,
>> I found maybe it's not true.
>>      in rabbit_msg_store.erl , when write a message to a file, it will record
>> pending confirms,.and sync these confirms very 25 milliseconds, the problem is
>> the file is cached file, so after sended the confirms, the messages may not
>> have been written to disk. am i correct?
> The confirm is sent after fsyncing the msg store file (via
> `file_handle_cache:sync/1'), which flushes all the in-memory changes to
> disc. I'm not sure what you mean by "the file is a cached file".
>
> --
> Francesco * Often in error, never in doubt
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