Going from average ~100ms to ~10ms or so. The previous query had a
tendency to be much slower sometimes, let's see if this cache also takes
care of those outliers.
Migration script:
ALTER TABLE packages ADD COLUMN c_hasman boolean NOT NULL DEFAULT FALSE;
DROP INDEX packages_system_name_key;
CREATE UNIQUE INDEX packages_system_name_key ON packages (system, name) INCLUDE (id, c_hasman, dead);
UPDATE packages SET c_hasman = NOT c_hasman
WHERE c_hasman <> EXISTS(SELECT 1 FROM package_versions pv WHERE pv.package = packages.id AND EXISTS(SELECT 1 FROM files f WHERE f.pkgver = pv.id));
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