Re: [pve-devel] [PATCH manager 1/1] api: journal: stream the journal data to the client

[Stoiko Ivanov <s.ivanov@proxmox.com>]

On Wed, 24 Nov 2021 18:46:04 +0100
Thomas Lamprecht <t.lamprecht@proxmox.com> wrote:

> On 24.11.21 18:32, Stoiko Ivanov wrote:
> > Huge thanks for addressing this so quickly and elegantly!
> > 
> > One question/nit:
> > 
> > On Wed, 24 Nov 2021 15:47:48 +0100
> > Dominik Csapak <d.csapak@proxmox.com> wrote:
> >   
> >> instead of accumulating the whole output of 'mini-journalreader' in
> >> the api call (this can be quite big), use the download mechanic of the
> >> http-server to stream the output to the client.
> >>
> >> we lose some error handling possibilities, but we do not have
> >> to allocate anything here, and since perl does not free memory after
> >> allocating[0] this is our desired behaviour.
> >>
> >> to keep api compatiblitiy, we need to give the journalreader the '-j'
> >> flag to let it output json.
> >>
> >> also tell the http server that the encoding is gzip and pipe
> >> the output through it.
> >>
> >> 0: https://perldoc.perl.org/perlfaq3#How-can-I-free-an-array-or-hash-so-my-program-shrinks?
> >>
> >> Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
> >> ---
> >>  PVE/API2/Nodes.pm | 22 ++++++++++++++--------
> >>  1 file changed, 14 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/PVE/API2/Nodes.pm b/PVE/API2/Nodes.pm
> >> index 565cbccc..d57a1937 100644
> >> --- a/PVE/API2/Nodes.pm
> >> +++ b/PVE/API2/Nodes.pm
> >> @@ -819,19 +819,25 @@ __PACKAGE__->register_method({
> >>  	my $rpcenv = PVE::RPCEnvironment::get();
> >>  	my $user = $rpcenv->get_user();
> >>  
> >> -	my $cmd = ["/usr/bin/mini-journalreader"];
> >> +	my $cmd = ["/usr/bin/mini-journalreader", "-j"];
> >>  	push @$cmd, '-n', $param->{lastentries} if $param->{lastentries};
> >>  	push @$cmd, '-b', $param->{since} if $param->{since};
> >>  	push @$cmd, '-e', $param->{until} if $param->{until};
> >> -	push @$cmd, '-f', $param->{startcursor} if $param->{startcursor};
> >> -	push @$cmd, '-t', $param->{endcursor} if $param->{endcursor};
> >> +	push @$cmd, '-f', PVE::Tools::shellquote($param->{startcursor}) if $param->{startcursor};
> >> +	push @$cmd, '-t', PVE::Tools::shellquote($param->{endcursor}) if $param->{endcursor};
> >> +	push @$cmd, ' | gzip ';  
> > Not sure which would be more efficient - but the http-server does support
> > gzipping the result from the API  
> 
> It has no api result in that case, it just returns the open file handle and anyevent
> can then stream that directly, see the response_stream method in PVE::APIServer::AnyEvent.
Thanks for the explanation! (and sorry for the noise)

> 
> > might it make sense to let the worker do the gzip-encoding vs. forking
> > gzip here?  
> 
> contrary to our rust infra from PBS we do not have a streaming encoder directly in
> the server that we can just layer in between, pve-http-server can currently only compress
> if it has the whole response, and that's, which is what we want to avoid here.
> 
> The response method explicitly guards for the stream-an-fh case, AnyEvent.pm line 325:
> 
> if ($content && !$stream_fh) {
>    # ...
>    my $comp = Compress::Zlib::memGzip($content);
> 
> What we can do though is compress directly in the mini-journal reader, but that'll be
> way easier once we rewrite in in rust (heh), as then we can reuse our existing
> infrastructure to just layer that in-between.