Re: DSM segment handle generation in background workers

On Thu, Oct 11, 2018 at 5:51 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The comment adjacent to the change in InitStandaloneProcess bothers me.
> In particular, it points out that what BackendRun() is currently doing
> creates more entropy in the process's random seed than what you have
> here: MyStartTime is only good to the nearest second, whereas the code
> you removed from BackendRun() factors in fractional seconds to whatever
> the precision of GetCurrentTimestamp is.  This does not seem like an
> improvement.

True.

> I'm inclined to think we should refactor a bit more aggressively so
> that, rather than dumbing backends down to the standard of other
> processes, we make them all use the better method.  A reasonable way
> to approach this would be to invent a global variable MyStartTimestamp
> beside MyStartTime, and initialize both of them in the places that
> currently initialize the latter, using code like that in
> BackendInitialize:
>
>         /* save process start time */
>         port->SessionStartTime = GetCurrentTimestamp();
>         MyStartTime = timestamptz_to_time_t(port->SessionStartTime);
>
> and then this new InitRandomSeeds function could adopt BackendRun's
> seed initialization method instead of the stupider way.

Ok, done.

With MyStartTimestamp in the picture, port->SessionStartTime is
probably redundant... <looks around> and in fact the comment in struct
Port says it shouldn't even be there.  So... I removed it, and used
the new MyStartTimestamp in the couple of places that wanted it.
Thoughts?

> Possibly it'd be sane to merge the MyStartTime* initializations
> and the srandom resets into one function, not sure.

+1

The main difficulty was coming up with a name for the function that
does those things.  I went with InitProcessGlobals().  Better
suggestions welcome.

-- 
Thomas Munro
http://www.enterprisedb.com