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Re: increasing the default WAL segment size

Michael Paquier <michael.paquier@gmail.com>

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From: Michael Paquier <michael.paquier@gmail.com>
To: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: PostgreSQL mailing lists <pgsql-hackers@postgresql.org>, Beena Emerson <memissemerson@gmail.com>
Date: 2017-01-03T12:16:09Z
Lists: pgsql-hackers 
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. Actually, why not just having an equivalent of the SQL
command and be able to query parameter values?
-- 
Michael

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.