[OASIS Issue Tracker] Commented: (MQTT-10) Should Qos=0 retained messages be persisted in the server?

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    [ http://tools.oasis-open.org/issues/browse/MQTT-10?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33390#action_33390 ] 

Raphael Cohen commented on MQTT-10:
-----------------------------------

My 2 cents:-

I think it depends on what someone means to achieve by doing a server restart. Some scenarios:-

- Physical Host in someone's data centre, administrator wants to try to 'fix' a broker configuration issue, so does a restart to flush configuration (eg invoke-rc.d restart x on classic init.d based systems). Probably does want to drop in-memory messages (which might be == QoS 0)

- Virtual Host in the cloud, underlying infrastructure needs patching, server stopped and restarted, end user of messaging probably shouldn't know or have to care

- Physical or Virtual Host, kernel needs patching, but there's a 5 9s SLA (uggh but true), so a quick restart is needed. So either restart doesn't cause QoS to be lost (as user shouldn't be ware) or it does (to satisfy fast restart goals, so any in-memory QoS aren't flushed to disk first).

- 9 to 5 system (a lot of trading systems run only daily), powered off at end of day, probably QoS 0 and everything else can be destroyed.

So really, it comes down to what level of g'tee a provider (ie server infrastructure + broker)  (either internal datacentre, or virtuals, or cloud) interprets as QoS 0. Perhaps we should offer guidance only / use a MAY (eg, a conforming implementation MAY decide to not retain QoS 0 retained messages over server restarts).


> Should Qos=0 retained messages be persisted in the server?
> ----------------------------------------------------------
>
>                 Key: MQTT-10
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-10
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>         Environment: MQTT server
>            Reporter: Andrew Banks
>
> The current specification states that :
> Retained messages should be kept over restarts of the server.
> Is this correct even for Qos=0 retained publications?

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