[pve-devel] [PATCH manager] Jobs: fix scheduling when updating on unrelated nodes

[Dominik Csapak]

On 7/15/22 10:51, Fabian Ebner wrote:
> In the subject, I wouldn't call the nodes "unrelated". How about "after
> updating job from a different node"?
> 

sure makes sense

> Am 14.07.22 um 09:42 schrieb Dominik Csapak:
>> since the jobs are configured clusterwide in pmxcfs, a user can use any
>> node to update the config of them. for some configs (schedule/enabled)
>> we need to update the last runtime in the state file, but this
>> is sadly only node-local.
>>
>> to also update the state file on the other nodes, we introduce
>> a new 'update_job_props' function that saves relevant properties from
>> the config to the statefile each round of the scheduler if they changed.
>>
>> this way, we can detect changes in those and update the last runtime too.
>>
>> the only situation where that would not be enough is when a user
>> changes schedules and back to the original one within a single minute
>> (so between scheduler runs). in that case, the other nodes won't
>> detect that change, but it seems to be a rather unlikely edge case
>> that we can ignore.
> 
> Even with that edge case, there's no effect on when the job actually
> runs, or? Just the 'updated' time stamp in the job state will not be
> correct (from a global perspective) on the other nodes until the job
> runs again.

the more i think about it, the more i think you're right

for some reason i thought that no updating the timestamp in
this scenario might mean that it can run instantly, but that
can only happen when the last runtime is older than it should be.
(e.g. even when the node is offline/pvescheduler is not running,
we'll (by default) update the timestamp on the first iteration)

so yes, i think we can safely ignore that edge case then
> 
>>
>> if we really want to solve that too, we'd have to save the 'updated'
>> timestamp in the config too, just to sync it to the job state file
>> later.
>>
>> in 'synchronize_job_states_with_config' we switch from reading the
>> jobstate unconditionally to check the existing of the statefile
>> (which is the only condition where that can return undef anyway)
> 
> typos:
> s/existing/existence/
> 'where' should be dropped

ok

> 
>> so that we don't read the file multiple times each round.
>>
>> Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
> 
> What about starting_job and started_job? The saved_props are lost when
> that function writes its new state. Maybe there should be a wrapper for
> updating the job state that always preserves certain properties.

i guess you're right, but currently that makes no difference since
we're only concerned with not running too early which is irrelevant
for the starting/started case
(and it'll be synced up again after the next iteration)

> 
>> ---
>>   PVE/Jobs.pm | 62 ++++++++++++++++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 57 insertions(+), 5 deletions(-)
>>
>> diff --git a/PVE/Jobs.pm b/PVE/Jobs.pm
>> index 1091bc22..822f0454 100644
>> --- a/PVE/Jobs.pm
>> +++ b/PVE/Jobs.pm
>> @@ -25,6 +25,8 @@ my $default_state = {
>>       time => 0,
>>   };
>>   
>> +my $saved_props = [qw(enabled schedule)];
> 
> Maybe move update_job_props to right below here, so the comment
> describing the use is closer? Or maybe something like
> runtime_updating_props is more descriptive?
> 
>> +
>>   # lockless, since we use file_get_contents, which is atomic
>>   sub read_job_state {
>>       my ($jobid, $type) = @_;
>> @@ -93,8 +95,15 @@ sub update_job_stopped {
>>   		upid => $state->{upid},
>>   	    };
>>   
>> -	    if ($state->{updated}) { # save updated time stamp
>> -		$new_state->{updated} = $state->{updated};
>> +	    # save some old props
>> +	    if (my $updated = $state->{updated}) {
>> +		$new_state->{updated} = $updated;
>> +	    }
>> +
>> +	    for my $prop (@$saved_props) {
>> +		if (defined($state->{$prop})) {
>> +		    $new_state->{$prop} = $state->{$prop};
>> +		}
>>   	    }
>>   
>>   	    my $path = $get_state_file->($jobid, $type);
>> @@ -105,7 +114,7 @@ sub update_job_stopped {
>>   
>>   # must be called when the job is first created
>>   sub create_job {
>> -    my ($jobid, $type) = @_;
>> +    my ($jobid, $type, $cfg) = @_;
> 
> The caller in PVE/API2/Backup.pm could also be adapted to this change.
> Although I suppose any new job will be caught by
> synchronize_job_states_with_config, like on nodes different from the one
> on which it was created.

true, better still to give the config right away

> 
>>   
>>       lock_job_state($jobid, $type, sub {
>>   	my $state = read_job_state($jobid, $type) // $default_state;
>> @@ -115,6 +124,11 @@ sub create_job {
>>   	}
>>   
>>   	$state->{time} = time();
>> +	for my $prop (@$saved_props) {
>> +	    if (defined($cfg->{$prop})) {
>> +		$state->{$prop} = $cfg->{$prop};
>> +	    }
>> +	}
>>   
>>   	my $path = $get_state_file->($jobid, $type);
>>   	PVE::Tools::file_set_contents($path, encode_json($state));
>> @@ -192,6 +206,39 @@ sub update_last_runtime {
>>       });
>>   }
>>   
>> +# saves some properties of the jobcfg into the jobstate so we can track
>> +# them on different nodes (where the update was not done)
>> +# and update the last runtime when they change
>> +sub update_job_props {
> 
> update_saved_props or detect_changed_runtime_props might be a bit more
> telling

then i'd opt for 'detect_changed_runtime_props' since it's a bit more
verbose imho

> 
>> +    my ($jobid, $type, $cfg) = @_;
>> +
>> +    lock_job_state($jobid, $type, sub {
>> +	my $old_state = read_job_state($jobid, $type) // $default_state;
>> +
>> +	my $updated = 0;
>> +	for my $prop (@$saved_props) {
>> +	    my $old_prop = $old_state->{$prop} // '';
>> +	    my $new_prop = $cfg->{$prop} // '';
>> +	    next if "$old_prop" eq "$new_prop";
>> +
>> +	    if (defined($cfg->{$prop})) {
>> +		$old_state->{$prop} = $cfg->{$prop};
>> +	    } else {
>> +		delete $old_state->{$prop};
>> +	    }
>> +
>> +	    $updated = 1;
>> +	}
>> +
>> +	return if !$updated;
>> +	$old_state->{updated} = time();
>> +
>> +	my $path = $get_state_file->($jobid, $type);
>> +	PVE::Tools::file_set_contents($path, encode_json($old_state));
>> +    });
>> +}
>> +
>> +
>>   sub get_last_runtime {
>>       my ($jobid, $type) = @_;
>>