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Re: increasing the default WAL segment size

Beena Emerson <memissemerson@gmail.com>

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From: Beena Emerson <memissemerson@gmail.com>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Date: 2017-01-05T11:39:05Z
Lists: pgsql-hackers 
Hello,

On Tue, Jan 3, 2017 at 5:46 PM, Michael Paquier <michael.paquier@gmail.com>
wrote:

> On Tue, Jan 3, 2017 at 6:23 AM, Jim Nasby <Jim.Nasby@bluetreble.com>
> wrote:
> > +               /* Check if wal_segment_size is in the power of 2 */
> > +               for (i = 0;; i++, pow2 = pow(2, i))
> > +                       if (pow2 >= wal_segment_size)
> > +                               break;
> > +
> > +               if (wal_segment_size != 1 && pow2 > wal_segment_size)
> > +               {
> > +                       fprintf(stderr, _("%s: WAL segment size must be
> in the power of 2\n"), progname);
> > +                       exit(1);
> > +               }
>
> I recall taht pow(x, 2) and x * x result usually in the same assembly
> code, but pow() can never be more optimal than a simple
> multiplication. So I'd think that it is wiser to avoid it in this code
> path. Documentation is missing for the new replication command
> SHOW_WAL_SEG.


As mentioned earlier, documents are not fully updated.


> Actually, why not just having an equivalent of the SQL
> command and be able to query parameter values?
>

This patch only needed the wal_segment_size and hence I made this specific
command.
How often and why would we need other parameter values in the replication
connection?
Making it a more general command to fetch any parameter can be a separate
topic. If it gets consensus, maybe it could be done and used here.


Thank you,

Beena Emerson

Have a Great Day!

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Make WAL segment size configurable at initdb time.

  2. Perform only one ReadControlFile() during startup.

  3. Introduce BYTES unit for GUCs.

  4. Remove useless duplicate inclusions of system header files.

  5. Refactor other replication commands to use DestRemoteSimple.

  6. Add a SHOW command to the replication command language.

  7. Add a new DestReceiver for printing tuples without catalog access.

  8. Support fls().

  9. Extend yesterday's patch making BLCKSZ and RELSEG_SIZE configurable to also

  10. Commit the reasonably uncontroversial parts of J.R. Nield's PITR patch, to

  11. XLOG (also known as WAL -:)) Bootstrap/Startup/Shutdown.

  12. Transaction log manager core code.