Re: [DOC] Document concurrent index builds waiting on each other

On 2020-Nov-30, James Coleman wrote:

> On Mon, Nov 30, 2020 at 4:53 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> >
> > On 2020-Sep-30, Michael Paquier wrote:

> > Yeah, I think it might be more sensible to document this in
> > maintenance.sgml, as part of the paragraph that discusses removing
> > tuples "to save space".  But making it inline with the rest of the flow,
> > it seems to distract from higher-level considerations, so I suggest to
> > make it a footnote instead.
> 
> I have mixed feelings about wholesale moving it; users aren't likely
> to read the vacuum doc when considering how running CIC might impact
> their system, though I do understand why it otherwise fits there.

Makes sense.  ISTM that if we want to have a cautionary blurb CIC docs,
it should go in REINDEX CONCURRENTLY as well.

> > I'm not sure on the wording to use; what about this?
> 
> The wording seems fine to me.

Great, thanks.

> This is a replacement for what was 0002 earlier? And 0001 from earlier
> still seems to be a useful standalone patch?

0001 is the one that I got pushed yesterday, I think -- correct?
src/tools/git_changelog says:

Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Branch: master [58ebe967f] 2020-11-30 18:24:55 -0300
Branch: REL_13_STABLE [3fe0e7c3f] 2020-11-30 18:24:55 -0300
Branch: REL_12_STABLE [b2603f16a] 2020-11-30 18:24:55 -0300
Branch: REL_11_STABLE [ed9c9b033] 2020-11-30 18:24:55 -0300
Branch: REL_10_STABLE [d3bd36a63] 2020-11-30 18:24:55 -0300
Branch: REL9_6_STABLE [b3d33bf59] 2020-11-30 18:24:55 -0300
Branch: REL9_5_STABLE [968a537b4] 2020-11-30 18:24:55 -0300

    Document concurrent indexes waiting on each other
    
    Because regular CREATE INDEX commands are independent, and there's no
    logical data dependency, it's not immediately obvious that transactions
    held by concurrent index builds on one table will block the second phase
    of concurrent index creation on an unrelated table, so document this
    caveat.
    
    Backpatch this all the way back.  In branch master, mention that only
    some indexes are involved.
    
    Author: James Coleman <jtc331@gmail.com>
    Reviewed-by: David Johnston <david.g.johnston@gmail.com>
    Discussion: https://postgr.es/m/CAAaqYe994=PUrn8CJZ4UEo_S-FfRr_3ogERyhtdgHAb2WG_Ufg@mail.gmail.com