Hi,
I would like to restart from zero the voting on KIP-663 that proposes to
add methods to the Kafka Streams client to add and remove stream threads
during execution.
https://cwiki.apache.org/confluence/display/KAFKA/KIP-663%3A+API+to+Start+and+Shut+Down+Stream+Threads
Matthias, if you are still +1, please vote again.
Best,
Bruno
On 04.09.20 23:12, John Roesler wrote:
Hi Sophie,
Uh, oh, it's never a good sign when the discussion moves
into the vote thread :)
I agree with you, it seems like a good touch for
removeStreamThread() to return the name of the thread that
got removed, rather than a boolean flag. Maybe the return
value would be `null` if there is no thread to remove.
If we go that way, I'd suggest that addStreamThread() also
return the name of the newly created thread, or null if no
thread can be created right now.
I'm not completely sure if I think that callers of this
method would know exactly how many threads there are. Sure,
if a human being is sitting there looking at the metrics or
logs and decides to call the method, it would work out, but
I'd expect this kind of method to find its way into
automated tooling that reacts to things like current system
load or resource saturation. Those kinds of toolchains often
are part of a distributed system, and it's probably not that
easy to guarantee that the thread count they observe is
fully consistent with the number of threads that are
actually running. Therefore, an in-situ `int
numStreamThreads()` method might not be a bad idea. Then
again, it seems sort of optional. A caller can catch an
exception or react to a `null` return value just the same
either way. Having both add/remove methods behave similarly
is probably more valuable.
Thanks,
-John
On Thu, 2020-09-03 at 12:15 -0700, Sophie Blee-Goldman
wrote:
Hey, sorry for the late reply, I just have one minor suggestion. Since we
don't
make any guarantees about which thread gets removed or allow the user to
specify, I think we should return either the index or full name of the
thread
that does get removed by removeThread().
I know you just updated the KIP to return true/false if there are/aren't any
threads to be removed, but I think this would be more appropriate as an
exception than as a return type. I think it's reasonable to expect users to
have some sense to how many threads are remaining, and not try to remove
a thread when there is none left. To me, that indicates something wrong
with the user application code and should be treated as an exceptional case.
I don't think the same code clarify argument applies here as to the
addStreamThread() case, as there's no reason for an application to be
looping and retrying removeStreamThread() since if that fails, it's because
there are no threads left and thus it will continue to always fail. And if
the
user actually wants to shut down all threads, they should just close the
whole application rather than call removeStreamThread() in a loop.
While I generally think it should be straightforward for users to track how
many stream threads they have running, maybe it would be nice to add
a small utility method that does this for them. Something like
// Returns the number of currently alive threads
boolean runningStreamThreads();
On Thu, Sep 3, 2020 at 7:41 AM Matthias J. Sax <mj...@apache.org> wrote:
+1 (binding)
On 9/3/20 6:16 AM, Bruno Cadonna wrote:
Hi,
I would like to start the voting on KIP-663 that proposes to add methods
to the Kafka Streams client to add and remove stream threads during
execution.
https://cwiki.apache.org/confluence/display/KAFKA/KIP-663%3A+API+to+Start+and+Shut+Down+Stream+Threads
Best,
Bruno
