Merge ~cjwatson/launchpad:db-archive-file-history into launchpad:db-devel

[Colin Watson]

Add ArchiveFile.date_created and ArchiveFile.date_superseded

LP: #1765933

This is essentially the same as https://code.launchpad.net/~cjwatson/launchpad/db-archive-file-history/+merge/343750, converted to git and rebased on master, and with a new patch number since we've rebaselined the schema since I originally proposed this.

[William Grant (wgrant)]

Not terribly useful without indexes, but for the cold patch this is good.

It might, though, be interesting to clarify in the comments that date_superseded is when it ceased to hold its name -- it remains on disk for somewhat longer.

review: Approve (db)

e019f4e... by Colin Watson on 2020-04-08

Clarify meaning of ArchiveFile.date_superseded

diff --git a/database/schema/patch-2210-09-0.sql b/database/schema/patch-2210-09-0.sql
new file mode 100644
index 0000000..b4c3153
--- /dev/null
+++ b/database/schema/patch-2210-09-0.sql
@@ -0,0 +1,13 @@
+-- Copyright 2018 Canonical Ltd.  This software is licensed under the
+-- GNU Affero General Public License version 3 (see the file LICENSE).
+
+SET client_min_messages=ERROR;
+
+ALTER TABLE ArchiveFile
+    ADD COLUMN date_created timestamp without time zone,
+    ADD COLUMN date_superseded timestamp without time zone;
+
+COMMENT ON COLUMN ArchiveFile.date_created IS 'The date when this file was created.';
+COMMENT ON COLUMN ArchiveFile.date_superseded IS 'The date when this file ceased to hold its path in the archive, due to being removed or superseded by a newer version.';
+
+INSERT INTO LaunchpadDatabaseRevision VALUES (2210, 09, 0);