| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: should there be a hard-limit on the number of transactions pending undo? |
| Date: | 2019-07-29 20:01:54 |
| Message-ID: | CAH2-WzksYJ=Y8nK3QPbJGW5zwDZPAutf+mB4Z=twSWKbA7TdNQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jul 29, 2019 at 12:39 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> I think that indexes (or at least B-Tree indexes) will ideally almost
> always have tuples that are the latest versions with zheap. The
> exception is tuples whose ghost bit is set, whose visibility varies
> based on the MVCC snapshot in use. But the instant that the
> deleting/updating xact commits it becomes legal to recycle the old
> heap TID.
Sorry, I meant the instant the ghost bit index tuple cannot be visible
to any possible MVCC snapshot. Which, in general, will be pretty soon
after the deleting/updating xact commits.
--
Peter Geoghegan
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