Remove version_downloads.id

This column is no longer being used, and can be safely removed. Rolling
back this migration in production requires creating indexes
concurrently, which Diesel CLI doesn't support, so rolling back this
migration in production will require queries to be run manually. A
blocking version is included for development and testing

Author: sgrif

migrations/2019-03-22-174825_remove_version_downloads_pk/down.sql

@@ -0,0 +1,28 @@
+-- Diesel always runs migrations in a transaction, and we can't create indexes
+-- concurrently in a transaction. We can't block crate downloads on this, so
+-- just raise if we try to run this in production
+DO $$
+DECLARE
+  tmp_index_exists boolean;
+BEGIN
+  tmp_index_exists := (SELECT EXISTS (
+      SELECT * FROM pg_index
+        INNER JOIN pg_class
+          ON pg_class.oid = pg_index.indexrelid
+        WHERE relname = 'version_downloads_tmp'
+  ));
+  IF NOT tmp_index_exists THEN
+    IF (SELECT COUNT(*) FROM version_downloads) > 1000 THEN
+      RAISE EXCEPTION 'Indexes need to be created concurrently in production, manually create them and try again';
+    ELSE
+      ALTER TABLE version_downloads ADD COLUMN id SERIAL;
+      CREATE UNIQUE INDEX version_downloads_tmp ON version_downloads (id);
+      CREATE UNIQUE INDEX version_downloads_unique ON version_downloads (version_id, date);
+      CREATE UNIQUE INDEX index_version_downloads_not_processed ON version_downloads (id) WHERE processed = false;
+    END IF;
+  END IF;
+END $$;
+
+ALTER TABLE version_downloads
+  DROP CONSTRAINT version_downloads_pkey,
+  ADD CONSTRAINT version_downloads_pkey PRIMARY KEY USING INDEX version_downloads_tmp;

migrations/2019-03-22-174825_remove_version_downloads_pk/up.sql

@@ -0,0 +1,6 @@
+-- ALERT! DESTRUCTIVE MIGRATION
+-- DO NOT DEPLOY UNTIL PREVIOUS COMMIT IS DEPLOYED
+ALTER TABLE version_downloads
+  DROP CONSTRAINT version_downloads_pkey,
+  ADD CONSTRAINT version_downloads_pkey PRIMARY KEY USING INDEX version_downloads_unique,
+  DROP COLUMN id;