Horton

Re: [Proposal] Fully WAL logged CREATE DATABASE - No Checkpoints

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Ashutosh Sharma <ashu.coek88@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>, Bruce Momjian <bruce@momjian.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Andrew Dunstan <andrew@dunslane.net>, Heikki Linnakangas <hlinnaka@iki.fi>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-03-20T05:34:39Z
Lists: pgsql-hackers 
On Sun, Mar 20, 2022 at 12:03 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Fri, Mar 18, 2022 at 12:39 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > > One question that occurred to me when looking this over is whether, or
> > > why, it's safe against concurrent smgr invalidations.
> >
> > We are only accessing the smgr of the source database and the
> > destination database.  And there is no one else that can be connected
> > to the source db and the destination db is not visible to anyone.  So
> > do we really need to worry about the concurrent smgr invalidation?
> > What am I missing?
>
> A sinval reset can occur at any moment due to an overflow of the
> queue. That acts as a universal reset of everything. So you can't
> reason on the basis of what somebody might be sending.

I thought that way because IIUC, when we are locking the database
tuple we are ensuring that we are calling
ReceiveSharedInvalidMessages() right?   And IIUC
ReceiveSharedInvalidMessages(), is designed such a way that it will
consume all the outstanding messages and that's the reason it loops
multiple times if it identifies that the queue is full.  And if my
assumption here is correct then I think it is also correct that now we
only need to worry about anyone generating new invalidations and that
is not possible in this case.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. When using the WAL-logged CREATE DATABASE strategy, bulk extend.

  2. Avoid using a fake relcache entry to own an SmgrRelation.

  3. Fix data-corruption hazard in WAL-logged CREATE DATABASE.

  4. initdb: When running CREATE DATABASE, use STRATEGY = WAL_COPY.

  5. Simplify a needlessly-complicated regular expression.

  6. In 020_createdb.pl, change order of command-line arguments.

  7. Add new block-by-block strategy for CREATE DATABASE.

  8. Fix replay of create database records on standby

  9. Refactor code for reading and writing relation map files.

  10. Replace RelationOpenSmgr() with RelationGetSmgr().

  11. Refactor the fsync queue for wider use.