zookeeper-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From kishore g <g.kish...@gmail.com>
Subject Re: Maximum size of a snapshot
Date Wed, 17 Jul 2013 01:46:57 GMT
Thanks Thawan. Another question to follow up, so lets say client c1 is
connected to leader and leader fails. Now c1 is trying to connect to
another zk server but all servers are busy loading snapshot and can take a
minute or two. According to Flavio zk servers dont accept any request while
synchronization, but most clients dont keep that high connection timeout.
So does this mean clients will timeout on connection?. Is my understanding
correct or zk servers will accept connection requests but reject read/write
requests.

thanks,
Kishore G


On Tue, Jul 16, 2013 at 3:45 PM, Thawan Kooburat <thawan@fb.com> wrote:

> There is a plan to work on this optimization ZOOKEEPER-1674.
>
>
> --
> Thawan Kooburat
>
>
>
>
>
> On 7/16/13 1:37 PM, "kishore g" <g.kishore@gmail.com> wrote:
>
> >All servers in the quorum reading the snapshot from disk as part of the
> >synchronization phase. From Thawan's email it looks like when ever there
> >is
> >a leader election, all zk servers read the snapshot from disk. I am not
> >sure why all servers should reload the snapshot from disk as this
> >increases
> >unavailability time.
> >
> >
> >On Tue, Jul 16, 2013 at 12:35 PM, Flavio Junqueira
> ><fpjunqueira@yahoo.com>wrote:
> >
> >> The synchronization phase is part of the protocol and we use it to
> >> guarantee that we expose a consistent view of the state. During the
> >> synchronization phase, servers do not accept requests.
> >>
> >> Which behavior are you proposing we change, Kishore?
> >>
> >> -Flavio
> >>
> >> On Jul 16, 2013, at 7:04 PM, kishore g <g.kishore@gmail.com> wrote:
> >>
> >> > Thanks for clarification Flavio. Does this mean during the leader
> >> election,
> >> > both reads and writes are not supported?. Do we start a separate
> >> > thread/jira of changing this behavior?.
> >> >
> >> > thanks,
> >> > Kishore G
> >> >
> >> >
> >> > On Tue, Jul 16, 2013 at 9:16 AM, Flavio Junqueira
> >><fpjunqueira@yahoo.com
> >> >wrote:
> >> >
> >> >> The disk state should be the authoritative state of a server, so if
I
> >> >> remember correctly, we load the database as a way of validating the
> >>disk
> >> >> state. I don't claim that this is strictly necessary, but if we are
> >>to
> >> >> change it, then I would need to think this through.
> >> >>
> >> >> About leader election, if a leader loses support from a quorum of
> >> >> followers,
> >> >> then it will drop leadership. Any event that causes a follower to
> >>stop
> >> >> receiving messages from the leader or the follower to disconnect from
> >> the
> >> >> leader will make it stop supporting the current leader.
> >> >>
> >> >> -Flavio
> >> >>
> >> >> -----Original Message-----
> >> >> From: Sergey Maslyakov [mailto:evolvah@gmail.com]
> >> >> Sent: 16 July 2013 16:16
> >> >> To: user@zookeeper.apache.org
> >> >> Subject: Re: Maximum size of a snapshot
> >> >>
> >> >> And another extension on top of Kishore's question: do the
> >>reelections
> >> >> happen if the previously elected leader remains in the cluster? In
> >>other
> >> >> words, what events can trigger re-election and the corresponding
> >> temporary
> >> >> degradation of the service provided by Zookeeper?
> >> >>
> >> >>
> >> >> Thank you,
> >> >> /Sergey
> >> >>
> >> >>
> >> >> On Tue, Jul 16, 2013 at 2:21 AM, kishore g <g.kishore@gmail.com>
> >>wrote:
> >> >>
> >> >>> Regarding #2. Is that really true that during leader election every
> >> >>> machine reloads snapshot data from disk? Any reason why this is
> >>needed
> >> >>> unless it really needs to truncate or undo conflicting transactions
> >> >> already applied?
> >> >>>
> >> >>>
> >> >>> On Mon, Jul 15, 2013 at 9:50 PM, Thawan Kooburat <thawan@fb.com>
> >> wrote:
> >> >>>
> >> >>>> Max snapshot size:
> >> >>>>
> >> >>>> Here is my take on these issue,  others feel free to add or
> >>correct.
> >> >>>>
> >> >>>> 1. Depends on how much RAM your machine has.  Snapshot is should
be
> >> >>>> less than the available RAM since everything is loaded into
memory.
> >> >>>> 2. Depends on what is the availability guarantee that the client
> >> needs.
> >> >>>> If there is leader election, every machine need to reload the
data
> >> >>>> from disk. So the quorum will be down for at least the same
as
> >> >>>> snapshot
> >> >>> loading
> >> >>>> time. The session timeout on the client side should be at least
> >> >>>> longer than expected downtime during leader election.
> >> >>>>
> >> >>>> --
> >> >>>> Thawan Kooburat
> >> >>>>
> >> >>>>
> >> >>>>
> >> >>>>
> >> >>>>
> >> >>>> On 7/15/13 8:46 PM, "Sergey Maslyakov" <evolvah@gmail.com>
wrote:
> >> >>>>
> >> >>>>> I have a couple of sizing questions to the users and developers.
> >> >>>>> Hope,
> >> >>> you
> >> >>>>> don't mind answering those.
> >> >>>>>
> >> >>>>> What is the guideline for the maximum reasonable size of
a
> >>DataTree
> >> >>> that a
> >> >>>>> single ZK server can manage? If ZK server writes out a
snapshot of
> >> >>>>> about 1GB in size, is it pushed beyond the limits or is
it still
> >> >> manageable?
> >> >>> If
> >> >>>>> so, where is the critical threshold when ZK is really being
> >>abused?
> >> >>>>>
> >> >>>>> Similarly, how can I estimate the propagation delay of
a change
> >> >>>>> across
> >> >>> an
> >> >>>>> ensemble of three ZK servers?
> >> >>>>>
> >> >>>>>
> >> >>>>> Thank you,
> >> >>>>> /Sergey
> >> >>>>
> >> >>>>
> >> >>>
> >> >>
> >> >>
> >>
> >>
>
>

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