Merge ~wgrant/launchpad:bprdc-ios into launchpad:master

[William Grant]

Index BinaryPackageReleaseDownloadCount for index-only scans

Creating an index on binarypackagereleasedownloadcount (archive, binary_package_release, day, count) allows BinaryPackagePublishingHistory.getDailyDownloadTotals and Archive.getPackageDownloadCount to execute as index-only scans and not touch the heap at all. One sample query drops from 2789 page reads to 177.

Should be applied hot.

[Colin Watson (cjwatson)]

review: Approve (db)

diff --git a/database/schema/patch-2210-01-4.sql b/database/schema/patch-2210-01-4.sql
new file mode 100644
index 0000000..be8b2d2
--- /dev/null
+++ b/database/schema/patch-2210-01-4.sql
@@ -0,0 +1,8 @@
+-- Copyright 2020 Canonical Ltd.  This software is licensed under the
+-- GNU Affero General Public License version 3 (see the file LICENSE).
+
+CREATE INDEX binarypackagereleasedownloadcount__index_only_scan__idx
+    ON binarypackagereleasedownloadcount (
+	archive, binary_package_release, day, country, count);
+
+INSERT INTO LaunchpadDatabaseRevision VALUES (2210, 01, 4);