Re: increasing the default WAL segment size

On Tue, Feb 28, 2017 at 9:45 AM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)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

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