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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: Jim Nasby <Jim.Nasby@bluetreble.com>
Cc: Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Andres Freund <andres@anarazel.de>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-02-28T05:06:02Z
Lists: pgsql-hackers 
On Tue, Feb 28, 2017 at 9:45 AM, Jim Nasby <Jim.Nasby@bluetreble.com> wrote:

> On 2/24/17 6:30 AM, Kuntal Ghosh wrote:
>
>> * You're considering any WAL file with a power of 2 as valid. Suppose,
>> the correct WAL seg size is 64mb. For some reason, the server
>> generated a 16mb invalid WAL file(maybe it crashed while creating the
>> WAL file). Your code seems to treat this as a valid file which I think
>> is incorrect. Do you agree with that?
>>
>
> Detecting correct WAL size based on the size of a random WAL file seems
> like a really bad idea to me.


> I also don't see the reason for #2... or is that how initdb writes out the
> correct control file?


The initdb module reads the size from the option provided and sets the
environment variable. This variable is read
in src/backend/access/transam/xlog.c and the ControlFile written.
Unlike pg_resetwal and pg_rewind, pg_basebackup cannot access the Control
file. It only accesses the wal log folder.  So we get the XLogSegSize from
the SHOW command using  replication connection.
As Kuntal pointed out, I might need to set it from  pg_receivewal.c as
well.

Thank you,

Beena Emerson

EnterpriseDB: https://www.enterprisedb.com/
The Enterprise PostgreSQL Company

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.