[pve-devel] [RFC PATCH manager] pvestatd: fix status server udp overflow

[Thomas Lamprecht]

On 2/27/20 4:14 PM, Dominik Csapak wrote:
> for big vms (many disks/nics) a single status update can be bigger
> than 20k (i measured about 21k for a vm with 31 disks and nics)
> which means that a single update can bring the length of
> $txn->{data} over 65k (if it was >45k before)

nice catch

> 
> we could reduce the limit when we send, but this would only move
> the problem, and we might run into it later on again
> 
> to solve it (mostly) completely, append the data to $txn->{olddata}
> as long as the new and old data together do not get over 65k
> 
> in that case, flush the olddata instead
> 
> on finish flush olddata and if somehow data was left in data, flush
> that also
> 
> one problem remains: if a single update from a vm/node/etc.. is over
> 65k, but this would require a bigger refactoring of the status
> plugins...

hmm, your changes seems wrong, or better said unnecessarily complicated
while not solving all issues..

I'll simply loop over data in 64k chunks if it's bigger than that and
send those out, simple package segmentation..

> 
> Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
> ---
>  PVE/ExtMetric.pm | 32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/PVE/ExtMetric.pm b/PVE/ExtMetric.pm
> index 14d98317..2f52b883 100644
> --- a/PVE/ExtMetric.pm
> +++ b/PVE/ExtMetric.pm
> @@ -34,10 +34,16 @@ sub update_all($$@) {
>  
>  	$plugin->$method($txn, @params);
>  
> -	if (length($txn->{data}) > 48000) {
> +	$txn->{olddata} //= '';
> +	$txn->{data} //= '';
> +
> +	if ((length($txn->{olddata}) + length($txn->{data})) > 65000) {
>  	    # UDP stack cannot handle messages > 65k, if we've alot of data we
>  	    # do smaller batch sends then, but keep the connection alive
> -	    transaction_flush($txn, 1);
> +	    transaction_flush($txn, 1, 1);
> +	    $txn->{olddata} = delete $txn->{data};
> +	} else {
> +	    $txn->{olddata} .= delete $txn->{data};
>  	}
>      }
>  }
> @@ -70,17 +76,27 @@ sub transactions_start {
>  }
>  
>  sub transaction_flush {
> -    my ($txn, $keepconnected) = @_;
> +    my ($txn, $keepconnected, $useolddata) = @_;
>  
>      if (!$txn->{connection}) {
>  	return if !$txn->{data}; # OK, if data was already sent/flushed
>  	die "cannot flush metric data, no connection available!\n";
>      }
> -    return if !defined($txn->{data}) || $txn->{data} eq '';
> +    if ($useolddata) {
> +	return if !defined($txn->{olddata}) || $txn->{olddata} eq '';
> +    } else {
> +	return if !defined($txn->{data}) || $txn->{data} eq '';
> +    }
>  
>      my $plugin = PVE::Status::Plugin->lookup($txn->{cfg}->{type});
>  
> -    my $data = delete $txn->{data};
> +    my $data;
> +    if ($useolddata) {
> +	$data = delete $txn->{olddata};
> +    } else {
> +	$data = delete $txn->{data};
> +    }
> +
>      eval { $plugin->send($txn->{connection}, $data) };
>      my $senderr = $@;
>  
> @@ -97,7 +113,11 @@ sub transactions_finish {
>      my ($transactions) = @_;
>  
>      for my $txn (@$transactions) {
> -	eval { transaction_flush($txn) };
> +	eval { transaction_flush($txn, undef, 1) };
> +	if ($txn->{data}) {
> +	    # should not happen, just for safety
> +	    eval { transaction_flush($txn) };
> +	}
>  	warn "$@" if $@;
>      }
>  }
>