ignite-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Andrey Kuznetsov <stku...@gmail.com>
Subject Re: Critical worker threads liveness checking drawbacks
Date Tue, 11 Sep 2018 15:54:41 GMT
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.

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message