Re: fixing old_snapshot_threshold's time->xid mapping

Thomas Munro <thomas.munro@gmail.com>

From: Thomas Munro <thomas.munro@gmail.com>

To: Dilip Kumar <dilipbalaut@gmail.com>

Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Kevin Grittner <kgrittn@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>

Date: 2020-04-21T10:14:01Z

Lists: pgsql-hackers

Attachments

v5-0001-Expose-oldSnapshotControl.patch (text/x-patch) patch v5-0001
v5-0002-contrib-old_snapshot-time-xid-mapping.patch (text/x-patch) patch v5-0002
v5-0003-Fix-bugs-in-MaintainOldSnapshotTimeMapping.patch (text/x-patch) patch v5-0003
v5-0004-Rewrite-the-snapshot_too_old-tests.patch (text/x-patch) patch v5-0004
v5-0005-Truncate-snapshot-too-old-time-map-when-CLOG-is-t.patch (text/x-patch) patch v5-0005
v5-0006-Add-TAP-test-for-snapshot-too-old-time-map-mainte.patch (text/x-patch) patch v5-0006

On Tue, Apr 21, 2020 at 2:05 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> As before, these two apply on top of Robert's patches (or at least his
> 0001 and 0002).

While trying to figure out if Robert's 0003 patch was correct, I added
yet another patch to this stack to test it.  0006 does basic xid map
maintenance that exercises the cases 0003 fixes, and I think it
demonstrates that they now work correctly.  Also some minor perl
improvements to 0005.  I'll attach 0001-0004 again but they are
unchanged.

Since confusion about head vs tail seems to have been at the root of
the bugs addressed by 0003, I wonder if we should also rename
head_{timestamp,offset} to oldest_{timestamp,offset}.

Commits

Remove the "snapshot too old" feature.
- f691f5b80a85 17.0 landed
Fix two bugs in MaintainOldSnapshotTimeMapping.
- 55b7e2f4d78d 14.0 landed
Add new 'old_snapshot' contrib module.
- aecf5ee2bb36 14.0 landed
Expose oldSnapshotControl definition via new header.
- f5ea92e8d620 14.0 landed