Hi Ismael,
This is something I can think of for migration plan:
So the migration plan can look something like this, with up conversion :
1) Currently lets say we have Broker at version x.
2) Currently we have clients at version x.
3) a) We move the version to Broker(x+1) : supports both tombstone and null
for log compaction.
b) We upgrade the client to version client(x+1) : if in the producer
client(x+1) the value is set to null, we will automatically set the
Tombstone bit internally. If the producer client(x+1) sets the tombstone
itself, well and good. For producer client(x), the broker will up convert
to have the tombstone bit. Broker(x+1) is supporting both. Consumer
client(x+1) will be aware of this and should be able to handle this. For
consumer client(x) we will down convert the message on the broker side.
c) At this point we will have to specify a warning or clearly specify
in docs that this behavior is about to be changed for log compaction.
4) a) In next release of the Broker(x+2), we say that only Tombstone is
used for log compaction on the Broker side. Clients(x+1) still is
supported.
b) We upgrade the client to version client(x+2) : if value is set to
null, tombstone will not be set automatically. The client will have to call
setTombstone() to actually set the tombstone.
We should compare this migration plan with the migration plan for magic
byte bump and do whatever looks good.
I am just worried that if we go down magic byte route, unless I am missing
something, it sounds like kafka will be stuck with supporting both null
value and tombstone bit for log compaction for life long, which does not
look like a good end state.
Thanks,
Mayuresh
On Wed, Nov 16, 2016 at 9:32 AM, Mayuresh Gharat <gharatmayures...@gmail.com
> wrote:
> Hi Ismael,
>
> That's a very good point which I might have not considered earlier.
>
> Here is a plan that I can think of:
>
> Stage 1) The broker from now on, up converts the message to have the
> tombstone marker. The log compaction thread does log compaction based on
> both null and tombstone marker. This is our transition period.
> Stage 2) The next release we only say that log compaction is based on
> tombstone marker. (Open source kafka makes this as a policy). By this time,
> the organization which is moving to this release will be sure that they
> have gone through the entire transition period.
>
> My only goal of doing this is that Kafka clearly specifies the end state
> about what log compaction means (is it null value or a tombstone marker,
> but not both).
>
> What do you think?
>
> Thanks,
>
> Mayuresh
> .
>
> On Wed, Nov 16, 2016 at 9:17 AM, Ismael Juma <ism...@juma.me.uk> wrote:
>
>> One comment below.
>>
>> On Wed, Nov 16, 2016 at 5:08 PM, Mayuresh Gharat <
>> gharatmayures...@gmail.com
>> > wrote:
>>
>> > - If we don't bump up the magic byte, on the broker side, the broker
>> > will always have to look at both tombstone bit and the value when do
>> the
>> > compaction. Assuming we do not bump up the magic byte,
>> > imagine the broker sees a message which does not have a tombstone bit
>> > set. The broker does not know when the message was produced (i.e.
>> > whether
>> > the message has been up converted or not), it has to take a further
>> > look at
>> > the value to see if it is null or not in order to determine if it is
>> a
>> > tombstone. The same logic has to be put on the consumer as well
>> because
>> > the
>> > consumer does not know if the message has been up converted or not.
>> > - If we upconvert while appending, this is not the case, right?
>>
>>
>> If I understand you correctly, this is not sufficient because the log may
>> have messages appended before it was upgraded to include KIP-87.
>>
>> Ismael
>>
>
>
>
> --
> -Regards,
> Mayuresh R. Gharat
> (862) 250-7125
>
--
-Regards,
Mayuresh R. Gharat
(862) 250-7125
