Re: Which process is actually doing the WAL writes/calls XLogFlush?

>On 06/23/2017 05:50 AM, Daniel Westermann wrote:
>> Hi all,
>>
>> as I did not find the answer in the documentation: Which background
>> process is actually doing the writes/flushes to the WAL? In the docs
>> ( https://www.postgresql.org/docs/10/static/wal-configuration.html ) it is
>> explained which internal functions are responsible for this:
>> XLogInsertRecord and XLogFlush but who does call them, especially the
>> flush? Is it the process for the user connection itself then which calls
>> this after commit?
>
>For all the details see here:
>
> https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/access/transam/README;h=4ae4715339e707ab5ed879a628aa96b73002ef43;hb=6a18e4bc2d13d077c52cf90a4c6ec68343808ba7 >
>>
>> Initially I thought it is the job of the wal_writer but according to
>> this blog post
>> ( http://www.cybertec.at/postgresql-writer-and-wal-writer-processes-explained/ )
>> this seems not to be true, right? Why do I need the wal_writer at all
>> then when synchronous_commit is set to something else than off?
>
>See here:
>
> https://www.postgresql.org/docs/9.6/static/wal-async-commit.html
Thanks, Adrian
It is clear now for the asynchronous stuff and wal_writer.
But I still did not figure out (or I am just not able to understand it from the README linked above)
which process is actually doing the write to the wal when you have synchronous commit set to on. Can
someone put some light on this?

Thanks
Daniel