From mboxrd@z Thu Jan  1 00:00:00 1970
From: Robin Roevens <robin.roevens@disroot.org>
To: development@lists.ipfire.org
Subject: Re: [PATCH] collectd: Do not sync
Date: Tue, 30 Jan 2024 20:50:02 +0100
Message-ID: <e7c6bffc3ac66756d89e41ca7f0732e9756ee14c.camel@sicho.home>
In-Reply-To: <20240130180152.4161491-1-michael.tremer@ipfire.org>
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Hi Michael, all

First, this mail does not contain critique, I'm only trying to learn,
if I'm wrong. But I think your remark about fixing hardware is not
correct?

In my understanding, sync synchronizes the not-yet-written data
currently in kernel managed cache memory (hence in volatile system
memory) to permanent storage. 
Normally storage hardware also has its own cache, which I presume you
are referring to, but I don't think sync cares or even knows about that
and that is/should be handled within the hardware itself. 
As soon as storage hardware returns an ACK on a write operation, sync
is happy. Not actually guaranteeing any physical write, only that all
to-be-written data is actually delivered to the storage hardware. 

I do agree that a (full) sync there is probably overkill. The content
of the config will be available to the collectd daemon whether it is
actually written on disk or still in cache, so no sync needed. 
If the server crashes/powercycles/... on that point, I think a possible
commented line that should be uncommented in that config is then
probably of the least concern.
On the other hand, a sync that blocks forever, is probably more of an
indicator that the hardware should be fixed, as this would mean sync
doesn't get all the ACK's it expects.

Please correct me if I'm wrong.


Regards
Robin

Michael Tremer schreef op di 30-01-2024 om 18:01 [+0000]:
> Calling a global sync operation manually is generally a bad idea as
> it
> can block for forever. If people have storage that does not retain
> anything that is being written to it, they need to fix their
> hardware.
> 
> Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
> ---
>  src/initscripts/system/collectd | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/src/initscripts/system/collectd
> b/src/initscripts/system/collectd
> index bb8a2f54f..56b799d56 100644
> --- a/src/initscripts/system/collectd
> +++ b/src/initscripts/system/collectd
> @@ -146,9 +146,6 @@ case "$1" in
>  			sed -i -e "s|^#LoadPlugin swap|LoadPlugin
> swap|g" /etc/collectd.conf
>  		fi
>  
> -		# sync after config update...
> -		sync
> -
>  		if [ $(date +%Y) -gt 2011 ]; then
>  			boot_mesg "Starting Collection daemon..."
>  			/usr/sbin/collectd -C /etc/collectd.conf
> -- 
> 2.39.2
> 
> 

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