[pgpool-hackers: 4053] Re: [pgpool-general: 7543] VIP with one node
Muhammad Usama
m.usama at gmail.com
Mon Nov 1 23:57:03 JST 2021
Hi Tatsuo,
On Mon, Nov 1, 2021 at 12:21 PM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> Hi Usama,
>
> Thank you for the patch. Unfortunately the patch does not apply to the
> master branch anymore. Can you please rebase it?
>
Please find the rebased patch
Thanks
Best regards
Muhammad Usama
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
>
> > Hi,
> >
> > So I have cooked up a WIP patch that implements the above discussed
> > behavior.
> >
> > The attached patch adds three new configuration parameters
> >
> > #wd_remove_shutdown_nodes = off
> > # when enabled properly shutdown
> > watchdog nodes get
> > # removed from the cluster and does
> not
> > count towards
> > # the quorum and consensus
> computations
> >
> > #wd_lost_node_removal_timeout = 0s
> > # Time after which the LOST watchdog
> > nodes get
> > # removed from the cluster and does
> not
> > count towards
> > # the quorum and consensus
> computations
> > # setting it to 0 will never remove
> the
> > LOST nodes
> >
> > #wd_initial_node_showup_time = 0s
> >
> > # Time to wait for Watchdog nodes to
> > connect to the cluster.
> > # After that time the nodes are
> > considered to be not part of
> > # the cluster and will not count
> towards
> > # the quorum and consensus
> computations
> > # setting it to 0 will wait forever
> >
> >
> > Keeping the default values for these parameters retains the existing
> > behavior.
> >
> >
> > Moreover, the patch also enhances the wd_watchdog_info utility to output
> > the current "Quorum State"
> >
> > for each watchdog node and "number of nodes require for quorum" and
> "valid
> > remote nodes count" as per
> >
> > the current status of watchdog cluster. This change might also require
> the
> > bump of pcp lib version.
> >
> >
> >
> > bin/pcp_watchdog_info -U postgres -v
> > Watchdog Cluster Information
> > Total Nodes : 3
> > Remote Nodes : 2
> >
> > *Valid Remote Nodes : 1*Alive Remote Nodes : 0
> >
> > *Nodes required for quorum: 2*Quorum state : QUORUM ABSENT
> > VIP up on local node : NO
> > Leader Node Name : localhost:9990 Darwin Usama-Macbook-Pro.local
> > Leader Host Name : localhost
> >
> > Watchdog Node Information
> > Node Name : localhost:9990 Darwin Usama-Macbook-Pro.local
> > ...
> > Status Name : LEADER
> >
> > *Quorum State : ACTIVE*
> > Node Name : localhost:9991 Darwin Usama-Macbook-Pro.local
> > ...
> > Status : 10
> > Status Name : SHUTDOWN
> > *Quorum State : ACTIVE*
> >
> > Node Name : Not_Set
> > ...
> > Status Name : DEAD
> >
> > *Quorum State : REMOVED-NO-SHOW*
> >
> > The patch is still in WIP state mainly because it lacks the documentation
> > updates, and I am
> > sharing it to get an opinion and suggestions on the behavior and
> > configuration parameter names.
> >
> > Thanks
> > Best regards
> > Muhammad Usama
> >
> >
> > On Mon, Aug 23, 2021 at 6:05 AM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> >
> >> Hi Usama,
> >>
> >> Sorry for late reply.
> >>
> >> From: Muhammad Usama <m.usama at gmail.com>
> >> Subject: Re: [pgpool-hackers: 3898] Re: [pgpool-general: 7543] VIP with
> >> one node
> >> Date: Thu, 22 Jul 2021 14:12:59 +0500
> >> Message-ID: <
> >> CAEJvTzXsKE2B0QMd0AjGBmXK6zocWZZcGU7yzzkSnmff0iAfqA at mail.gmail.com>
> >>
> >> > On Tue, Jul 20, 2021 at 4:40 AM Tatsuo Ishii <ishii at sraoss.co.jp>
> wrote:
> >> >
> >> >> >> Is it possible to configure watchdog to enable the lost node
> removal
> >> >> >> function only when a node is properly shutdown?
> >> >> >>
> >> >>
> >> >> > Yes if we disable the wd_lost_node_to_remove_timeout (by setting it
> >> to 0)
> >> >> > the lost node removal will only happen for properly shutdown nodes.
> >> >>
> >> >> Oh, I thought setting wd_lost_node_to_remove_timeout to 0 will keep
> >> >> the existing behavior.
> >> >>
> >> >
> >> > As there are two parts of the proposal, First one deals with removing
> the
> >> > lost node
> >> > from the cluster after wd_lost_node_to_remove_timeout amount of time.
> >> While
> >> > the
> >> > second part is about removing the properly shutdown nodes from the
> >> cluster.
> >> >
> >> > Now disabling the wd_lost_node_to_remove_timeout (setting it to 0)
> will
> >> > keep the
> >> > existing behaviour as far as removing the lost node portion of
> proposal
> >> is
> >> > concerned.
> >> >
> >> > While not counting the properly shutdown node as part of watchdog
> cluster
> >> > is not configurable (as per original proposal), So if we want to make
> >> this
> >> > part configurable
> >> > as well so that we can switch to 100% current behaviour then we can
> add
> >> > another
> >> > config parameter for that. like
> >> consider_shutdown_nodes_part_of_wd_cluster
> >> > = [on|off]
> >>
> >> +1 to add the new parameter.
> >>
> >> The reason is, some users may want to avoid split brain problem even
> >> if quorum/VIP is lost. Suppose there are two admins A for the system
> >> (OS), B for the database. B never wants to have the split brain
> >> possibility. If A shutdowns the system, B may not notice there are not
> >> enough nodes to form consensus anymore because if
> >> consider_shutdown_nodes_part_of_wd_cluster is on because the
> >> quorum/VIP will be kept until no node remains.
> >>
> >> In summary I think there are two use-cases for both
> >> consider_shutdown_nodes_part_of_wd_cluster is on and off.
> >> --
> >> Tatsuo Ishii
> >> SRA OSS, Inc. Japan
> >> English: http://www.sraoss.co.jp/index_en.php
> >> Japanese:http://www.sraoss.co.jp
> >>
> >>
>
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