Re: checkpoint clarifications needed

On 01/09/2017 06:47 AM, Tom DalPozzo wrote:
> https://www.postgresql.org/docs/9.5/static/wal-internals.html
> <https://www.postgresql.org/docs/9.5/static/wal-internals.html>
>
>
> "After a checkpoint has been made and the log flushed, the
> checkpoint's position is saved in the file pg_control. Therefore, at
> the start of recovery, the server first reads pg_control and then
> the checkpoint record; then it performs the REDO operation by
> scanning forward from the log position indicated in the checkpoint
> record. Because the entire content of data pages is saved in the log
> on the first page modification after a checkpoint (assuming
> full_page_writes is not disabled), all pages changed since the
> checkpoint will be restored to a consistent state."
>
>
> Hi, yes I know that, it's what I meant in my point 3). As it says first
> "the checkpoint's position (NOT the record)is saved in the file
> pg_control" then I had some doubt.

Yes it is just one piece of information stored in the file.

To see what else is stored there do:

pg_controldata -D your_cluster_data_directory

> Regards
> Pupillo
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com