Re: server auto-restarts and ipcs

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> "Ed L." <pgsql(at)bluepolka(dot)net> writes:
> > A power failure led to failed postmaster restart using 7.4.6 (see
> > output below). The short-term fix is usually to delete the pid file
> > and restart.
>
> Thinking some more about this ... does anyone know the algorithm used
> in Linux to assign shared memory segment IDs?

At least in 2.6 it seems to avoid reuse of ids by keeping a global counter
that is incremented every time a segment is created which ranges from 0..128k
that it multiplies by 32k and adds to the array index (which is reused
quickly).

So it doesn't seem plausible that there was an id collision unless this was
different in 2.4.20. However looking at his list of ids they're all separated
by multiples of 32769 which is what you would expect from this algorithm at
least until they start being reused.

--
greg