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From Maxim Muzafarov <maxmu...@gmail.com>
Subject Re: Critical worker threads liveness checking drawbacks
Date Thu, 27 Sep 2018 13:00:34 GMT
Folks,

I've found in `GridCachePartitionExchangeManager:2684` [1] (master branch)
exchange future wrapped
with double `blockingSectionEnd` method. Is it correct? I just want to
understand this change and
how should I use this in the future.

Should I file a new issue to fix this? I think here `blockingSectionBegin`
method should be used.

-------------
blockingSectionEnd();

try {
    resVer = exchFut.get(exchTimeout, TimeUnit.MILLISECONDS);
} finally {
    blockingSectionEnd();
}


[1]
https://github.com/apache/ignite/blob/master/modules/core/src/main/java/org/apache/ignite/internal/processors/cache/GridCachePartitionExchangeManager.java#L2684

On Wed, 26 Sep 2018 at 22:47 Vyacheslav Daradur <daradurvs@gmail.com> wrote:

> Andrey Gura, thank you for the answer!
>
> I agree that wrapping of 'init' method reduces the profit of watchdog
> service in case of PME worker, but in other cases, we should wrap all
> possible long sections on GridDhtPartitionExchangeFuture. For example
> 'onCacheChangeRequest' method or
> 'cctx.affinity().onCacheChangeRequest' inside because it may take
> significant time (reproducer attached).
>
> I only want to point out a possible issue which may allow to end-user
> halt the Ignite cluster accidentally.
>
> I'm sure that PME experts know how to fix this issue properly.
> On Wed, Sep 26, 2018 at 10:28 PM Andrey Gura <agura@apache.org> wrote:
> >
> > Vyacheslav,
> >
> > Exchange worker is strongly tied with
> > GridDhtPartitionExchangeFuture#init and it is ok. Exchange worker also
> > shouldn't be blocked for long time but in reality it happens.It also
> > means that your change doesn't make sense.
> >
> > What actually make sense it is identification of places which
> > intentionally blocking. May be some places/actions should be braced by
> > blocking guards.
> >
> > If you have failing tests please make sure that your failureHandler is
> > NoOpFailureHandler or any other handler with ignoreFailureTypes =
> > [CRITICAL_WORKER_BLOCKED].
> >
> >
> > On Wed, Sep 26, 2018 at 9:43 PM Vyacheslav Daradur <daradurvs@gmail.com>
> wrote:
> > >
> > > Hi Igniters!
> > >
> > > Thank you for this important improvement!
> > >
> > > I've looked through implementation and noticed that
> > > GridDhtPartitionsExchangeFuture#init has not been wrapped in blocked
> > > section. This means it easy to halt the node in case of longrunning
> > > actions during PME, for example when we create a cache with
> > > StoreFactrory which connect to 3rd party DB.
> > >
> > > I'm not sure that it is the right behavior.
> > >
> > > I filled the issue [1] and prepared the PR [2] with reproducer and
> possible fix.
> > >
> > > Andrey, could you please look at and confirm that it makes sense?
> > >
> > > [1] https://issues.apache.org/jira/browse/IGNITE-9710
> > > [2] https://github.com/apache/ignite/pull/4845
> > > On Mon, Sep 24, 2018 at 9:46 PM Andrey Kuznetsov <stkuzma@gmail.com>
> wrote:
> > > >
> > > > Denis,
> > > >
> > > > I've created the ticket [1] with short description of the
> functionality.
> > > >
> > > > [1] https://issues.apache.org/jira/browse/IGNITE-9679
> > > >
> > > >
> > > > пн, 24 сент. 2018 г. в 17:46, Denis Magda <dmagda@apache.org>:
> > > >
> > > > > Andrey K. and G.,
> > > > >
> > > > > Thanks, do we have a documentation ticket created? Prachi (copied)
> can help
> > > > > with the documentation.
> > > > >
> > > > > --
> > > > > Denis
> > > > >
> > > > > On Mon, Sep 24, 2018 at 5:51 AM Andrey Gura <agura@apache.org>
> wrote:
> > > > >
> > > > > > Andrey,
> > > > > >
> > > > > > finally your change is merged to master branch. Congratulations
> and
> > > > > > thank you very much! :)
> > > > > >
> > > > > > I think that the next step is feature that will allow signal
> about
> > > > > > blocked threads to the monitoring tools via MXBean.
> > > > > >
> > > > > > I hope you will continue development of this feature and provide
> your
> > > > > > vision in new JIRA issue.
> > > > > >
> > > > > >
> > > > > > On Tue, Sep 11, 2018 at 6:54 PM Andrey Kuznetsov <
> stkuzma@gmail.com>
> > > > > > wrote:
> > > > > > >
> > > > > > > David, Maxim!
> > > > > > >
> > > > > > > Thanks a lot for you ideas. Unfortunately, I can't adopt
all
> of them
> > > > > > right
> > > > > > > now: the scope is much broader than the scope of the change
I
> > > > > implement.
> > > > > > I
> > > > > > > have had a talk to a group of Ignite commiters, and we
agreed
> to
> > > > > complete
> > > > > > > the change as follows.
> > > > > > > - Blocking instructions in system-critical which may resonably
> last
> > > > > long
> > > > > > > should be explicitly excluded from the monitoring.
> > > > > > > - Failure handlers should have a setting to suppress some
> failures on
> > > > > > > per-failure-type basis.
> > > > > > > According to this I have updated the implementation: [1]
> > > > > > >
> > > > > > > [1] https://github.com/apache/ignite/pull/4089
> > > > > > >
> > > > > > > пн, 10 сент. 2018 г. в 22:35, David Harvey <
> syssoftsol@gmail.com>:
> > > > > > >
> > > > > > > > When I've done this before,I've needed to find the
oldest
> thread,
> > > > > and
> > > > > > kill
> > > > > > > > the node running that.   From a language standpoint,
Maxim's
> "without
> > > > > > > > progress" better than "heartbeat".   For example,
what I'm
> most
> > > > > > interested
> > > > > > > > in on a distributed system is which thread started
the work
> it has
> > > > > not
> > > > > > > > completed the earliest, and when did that thread last
make
> forward
> > > > > > > > process.     You don't want to kill a node because
a thread
> is
> > > > > waiting
> > > > > > on a
> > > > > > > > lock held by a thread that went off-node and has not
gotten a
> > > > > response.
> > > > > > > > If you don't understand the dependency relationships,
you
> will make
> > > > > > > > incorrect recovery decisions.
> > > > > > > >
> > > > > > > > On Mon, Sep 10, 2018 at 4:08 AM Maxim Muzafarov <
> maxmuzaf@gmail.com>
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > > > I think we should find exact answers to these
questions:
> > > > > > > > >  1. What `critical` issue exactly is?
> > > > > > > > >  2. How can we find critical issues?
> > > > > > > > >  3. How can we handle critical issues?
> > > > > > > > >
> > > > > > > > > First,
> > > > > > > > >  - Ignore uninterruptable actions (e.g. worker\service
> shutdown)
> > > > > > > > >  - Long I/O operations (should be a configurable
timeout
> for each
> > > > > > type of
> > > > > > > > > usage)
> > > > > > > > >  - Infinite loops
> > > > > > > > >  - Stalled\deadlocked threads (and\or too many
parked
> threads,
> > > > > > exclude
> > > > > > > > I/O)
> > > > > > > > >
> > > > > > > > > Second,
> > > > > > > > >  - The working queue is without progress (e.g.
disco,
> exchange
> > > > > > queues)
> > > > > > > > >  - Work hasn't been completed since the last
heartbeat
> (checking
> > > > > > > > > milestones)
> > > > > > > > >  - Too many system resources used by a thread
for the long
> period
> > > > > of
> > > > > > time
> > > > > > > > > (allocated memory, CPU)
> > > > > > > > >  - Timing fields associated with each thread
status
> exceeded a
> > > > > > maximum
> > > > > > > > time
> > > > > > > > > limit.
> > > > > > > > >
> > > > > > > > > Third (not too many options here),
> > > > > > > > >  - `log everything` should be the default behaviour
in all
> these
> > > > > > cases,
> > > > > > > > > since it may be difficult to find the cause after
the
> restart.
> > > > > > > > >  - Wait some interval of time and kill the hanging
node
> (cluster
> > > > > > should
> > > > > > > > be
> > > > > > > > > configured stable enough)
> > > > > > > > >
> > > > > > > > > Questions,
> > > > > > > > >  - Not sure, but can workers miss their heartbeat
> deadlines if CPU
> > > > > > loads
> > > > > > > > up
> > > > > > > > > to 80%-90%? Bursts of momentary overloads can
be
> > > > > > > > >     expected behaviour as a normal part of system
> operations.
> > > > > > > > >  - Why do we decide that critical thread should
monitor
> each other?
> > > > > > For
> > > > > > > > > instance, if all the tasks were blocked and unable
to run,
> > > > > > > > >     node reset would never occur. As for me,
a better
> solution is
> > > > > to
> > > > > > use
> > > > > > > > a
> > > > > > > > > separate monitor thread or pool (maybe both with
software
> > > > > > > > >     and hardware checks) that not only checks
heartbeats
> but
> > > > > > monitors the
> > > > > > > > > other system as well.
> > > > > > > > >
> > > > > > > > > On Mon, 10 Sep 2018 at 00:07 David Harvey <
> syssoftsol@gmail.com>
> > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > It would be safer to restart the entire
cluster than to
> remove
> > > > > the
> > > > > > last
> > > > > > > > > > node for a cache that should be redundant.
> > > > > > > > > >
> > > > > > > > > > On Sun, Sep 9, 2018, 4:00 PM Andrey Gura
<
> agura@apache.org>
> > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > Hi,
> > > > > > > > > > >
> > > > > > > > > > > I agree with Yakov that we can provide
some option
> that manage
> > > > > > worker
> > > > > > > > > > > liveness checker behavior in case of
observing that
> some worker
> > > > > > is
> > > > > > > > > > > blocked too long.
> > > > > > > > > > > At least it will  some workaround for
cases when node
> fails is
> > > > > > too
> > > > > > > > > > > annoying.
> > > > > > > > > > >
> > > > > > > > > > > Backups count threshold sounds good
but I don't
> understand how
> > > > > it
> > > > > > > > will
> > > > > > > > > > > help in case of cluster hanging.
> > > > > > > > > > >
> > > > > > > > > > > The simplest solution here is alert
in cases of
> blocking of
> > > > > some
> > > > > > > > > > > critical worker (we can improve WorkersRegistry
for
> this
> > > > > purpose
> > > > > > and
> > > > > > > > > > > expose list of blocked workers) and
optionally call
> system
> > > > > > configured
> > > > > > > > > > > failure processor. BTW, failure processor
can be
> extended in
> > > > > > order to
> > > > > > > > > > > perform any checks (e.g. backup count)
and decide
> whether it
> > > > > > should
> > > > > > > > > > > stop node or not.
> > > > > > > > > > > On Sat, Sep 8, 2018 at 3:42 PM Andrey
Kuznetsov <
> > > > > > stkuzma@gmail.com>
> > > > > > > > > > wrote:
> > > > > > > > > > > >
> > > > > > > > > > > > David, Yakov, I understand your
fears. But liveness
> checks
> > > > > deal
> > > > > > > > with
> > > > > > > > > > > > _critical_ conditions, i.e. when
such a condition is
> met we
> > > > > > > > conclude
> > > > > > > > > > the
> > > > > > > > > > > > node as totally broken, and there
is no sense to
> keep it
> > > > > alive
> > > > > > > > > > regardless
> > > > > > > > > > > > the data it contains. If we want
to give it a
> chance, then
> > > > > the
> > > > > > > > > > condition
> > > > > > > > > > > > (long fsync etc.) should not considered
as critical
> at all.
> > > > > > > > > > > >
> > > > > > > > > > > > сб, 8 сент. 2018 г. в
15:18, Yakov Zhdanov <
> > > > > > yzhdanov@apache.org>:
> > > > > > > > > > > >
> > > > > > > > > > > > > Agree with David. We need
to have an opporunity
> set backups
> > > > > > count
> > > > > > > > > > > threshold
> > > > > > > > > > > > > (at runtime also!) that will
not allow any
> automatic stop
> > > > > if
> > > > > > > > there
> > > > > > > > > > > will be
> > > > > > > > > > > > > a data loss. Andrey, what
do you think?
> > > > > > > > > > > > >
> > > > > > > > > > > > > --Yakov
> > > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > >
> > > > > > > > > > > > --
> > > > > > > > > > > > Best regards,
> > > > > > > > > > > >   Andrey Kuznetsov.
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > --
> > > > > > > > > --
> > > > > > > > > Maxim Muzafarov
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > --
> > > > > > > Best regards,
> > > > > > >   Andrey Kuznetsov.
> > > > > >
> > > > >
> > > >
> > > >
> > > > --
> > > > Best regards,
> > > >   Andrey Kuznetsov.
> > >
> > >
> > >
> > > --
> > > Best Regards, Vyacheslav D.
>
>
>
> --
> Best Regards, Vyacheslav D.
>
-- 
--
Maxim Muzafarov

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