Re: WAL page magic number (was Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct)

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> The correct way to reflect a change in WAL contents is to
>> bump the WAL page magic number.

> Browsing the history of XLOG_PAGE_MAGIC, it used to be incremented by
> one whenever the format changes, at least as long as it has been been in
> xlog_internal.h. It started at 0xD05B in 2005, and was incremented by
> one by each commit till 0xD062. But then the hot standby patch bumped it
> to 0xD166, and on March 19th Simon changed it to 0x9002, and on March
> 28th to 0x9003.

> Is there a plan somewhere on all that, or was it just random whacking?

Random whacking. Simon seems to have decided to try to make the number
mean something, but it never meant anything before. It's not a version
number, it's a magic identifier. We might need to avoid certain values
to prevent collisions with other file formats, so I'm suspicious of
trying to make it match up with some expectation.

regards, tom lane