Re: [Postgres-xc-developers] Patch to lock cluster

[Abbas B. <abb...@en...>]

On Thu, Feb 28, 2013 at 10:10 AM, Nikhil Sontakke <ni...@st...>wrote:

> Hi Abbas,
>
> What is exactly meant by locking the cluster here?
>

Means we disallow changes to the catalog during this phase.


>
> Do we disallow DDL during this phase?


Yes


> Do we allow only SELECT queries
> in this phase?


Yes and DMLs too are allowed.


> Am sorry, if I missed any earlier discussion on this.
> How is the backup consistent in this phase?
>

Because changes to the catalog were prohibited cluster wide.
Please note that we are only talking about the schema changes and not the
data changes since DMLs are allowed.


>
> Regards,
> Nikhils
>
> On Tue, Feb 19, 2013 at 12:37 PM, Abbas Butt
> <abb...@en...> wrote:
> > Hi,
> > Attached please find a patch that locks the cluster so that dump can be
> > taken to be restored on the new node to be added.
> >
> > To lock the cluster the patch adds a new GUC parameter called
> > xc_lock_for_backup, however its status is maintained by the pooler. The
> > reason is that the default behavior of XC is to release connections as
> soon
> > as a command is done and it uses PersistentConnections GUC to control the
> > behavior. We in this case however need a status that is independent of
> the
> > setting of PersistentConnections.
> >
> > Assume we have two coordinator cluster, the patch provides this behavior:
> >
> > Case 1: set and show
> > ====================
> > psql test -p 5432
> > set xc_lock_for_backup=yes;
> > show xc_lock_for_backup;
> >  xc_lock_for_backup
> > --------------------
> >  yes
> > (1 row)
> >
> > Case 2: set from one client show from other
> > ==================================
> > psql test -p 5432
> > set xc_lock_for_backup=yes;
> > (From another tab)
> > psql test -p 5432
> > show xc_lock_for_backup;
> >  xc_lock_for_backup
> > --------------------
> >  yes
> > (1 row)
> >
> > Case 3: set from one, quit it, run again and show
> > ======================================
> > psql test -p 5432
> > set xc_lock_for_backup=yes;
> > \q
> > psql test -p 5432
> > show xc_lock_for_backup;
> >  xc_lock_for_backup
> > --------------------
> >  yes
> > (1 row)
> >
> > Case 4: set on one coordinator, show from other
> > =====================================
> > psql test -p 5432
> > set xc_lock_for_backup=yes;
> > (From another tab)
> > psql test -p 5433
> > show xc_lock_for_backup;
> >  xc_lock_for_backup
> > --------------------
> >  yes
> > (1 row)
> >
> > pg_dump and pg_dumpall seem to work fine after locking the cluster for
> > backup but I would test these utilities in detail next.
> >
> > Also I have yet to look in detail that standard_ProcessUtility is the
> only
> > place that updates the portion of catalog that is dumped. There may be
> some
> > other places too that need to be blocked for catalog updates.
> >
> > The patch adds no extra warnings and regression shows no extra failure.
> >
> > Comments are welcome.
> >
> > --
> > Abbas
> > Architect
> > EnterpriseDB Corporation
> > The Enterprise PostgreSQL Company
> >
> > Phone: 92-334-5100153
> >
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>
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-- 
--
Abbas
Architect
EnterpriseDB Corporation
The Enterprise PostgreSQL Company

Phone: 92-334-5100153

Website: www.enterprisedb.com
EnterpriseDB Blog: http://blogs.enterprisedb.com/
Follow us on Twitter: http://www.twitter.com/enterprisedb

This e-mail message (and any attachment) is intended for the use of
the individual or entity to whom it is addressed. This message
contains information from EnterpriseDB Corporation that may be
privileged, confidential, or exempt from disclosure under applicable
law. If you are not the intended recipient or authorized to receive
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the sender immediately by reply e-mail and delete this message.