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Re: increasing the default WAL segment size

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Jim Nasby <Jim.Nasby@bluetreble.com>, Michael Paquier <michael.paquier@gmail.com>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>, Beena Emerson <memissemerson@gmail.com>
Date: 2017-01-09T19:40:55Z
Lists: pgsql-hackers 
On 10 January 2017 at 07:40, Robert Haas <robertmhaas@gmail.com> wrote:
> On Sat, Jan 7, 2017 at 7:45 PM, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:
>> Well, now that there's 3 places that need to do almost the same thing, I
>> think it'd be best to just centralize this somewhere. I realize that's not
>> going to save any significant amount of code, but it would make it crystal
>> clear what's going on (assuming the excellent comment above RIGHTMOST_ONE
>> was kept).
>
> Hmm.  This sounds a lot like what fls() and my_log2() also do.  I've
> been quietly advocating for fls() because we only provide an
> implementation in src/port if the operating system doesn't have it,
> and the operating system may have an implementation that optimizes to
> a single machine-language instruction (bsrl on x86, I think, see
> 4f658dc851a73fc309a61be2503c29ed78a1592e).  But the fact that our
> src/port implementation uses a loop instead of the RIGHTMOST_ONE()
> trick seems non-optimal.

It does really sound like we need a bitutils.c as mentioned in [1].
It would be good to make use of GCC's __builtin_popcount [2] instead
of the number_of_ones[] array in bitmapset.c. It should be a bit
faster and less cache polluting.

[1] https://www.postgresql.org/message-id/14578.1462595165@sss.pgh.pa.us
[2] https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html


-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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.