changelog ID as a sequence

As noted elsewhere, auto-increment sequences in postgres, mysql, and
cockroach can have gaps: when transactions that increment a number are
rolled back, a "gap" is left.

I didn't realize this, and it's problematic for the external changelog
API. I'll need to re-write the changelog inserter to query for the
current highest number when inserting, which is unfortunate and might
slow down bulk imports.

2 files changed, 5 insertions, 1 deletions

diff --git a/rust/migrations/2018-05-12-001226_init/down.sql b/rust/migrations/2018-05-12-001226_init/down.sql
index 3f796db6..7667d122 100644
--- a/rust/migrations/2018-05-12-001226_init/down.sql
+++ b/rust/migrations/2018-05-12-001226_init/down.sql
@@ -31,3 +31,5 @@ DROP TABLE IF EXISTS abstracts CASCADE;
 DROP TABLE IF EXISTS editor CASCADE;
 DROP TABLE IF EXISTS editgroup CASCADE;
 DROP TABLE IF EXISTS changelog CASCADE;
+
+DROP SEQUENCE IF EXISTS changelog_seq CASCADE;
diff --git a/rust/migrations/2018-05-12-001226_init/up.sql b/rust/migrations/2018-05-12-001226_init/up.sql
index 6b0e9c6e..3ca954ca 100644
--- a/rust/migrations/2018-05-12-001226_init/up.sql
+++ b/rust/migrations/2018-05-12-001226_init/up.sql
@@ -30,8 +30,10 @@ ALTER TABLE editor
     ADD CONSTRAINT editor_editgroupid_fkey FOREIGN KEY (active_editgroup_id)
         REFERENCES editgroup(id);
 
+CREATE SEQUENCE changelog_seq START 1 INCREMENT 1;
+
 CREATE TABLE changelog (
-    id                  BIGSERIAL PRIMARY KEY,
+    id                  BIGINT PRIMARY KEY DEFAULT nextval('changelog_seq'),
     editgroup_id        UUID REFERENCES editgroup(id) NOT NULL,
     timestamp           TIMESTAMP WITHOUT TIME ZONE DEFAULT now() NOT NULL
 );