Create fake revisions for every commit in the base of a linked package

This is a rather complex operation, but whenever a package changes in
Factory, the inherited package gets a shadow revision consisting of the
3-way merge. If this happens due to a request being accepted, this is
actually in most cases also commited by 'buildservice-autocommit',
so we're making sure this is always happening (and are actually
duplicating revisions in cases that we filter out later as empty
commits).

To differenciate the fake revisions from the real revisions, I add
a fraction part

lib/db.py

@@ -1,4 +1,7 @@
+import logging
+
 import psycopg2
+from psycopg2.extras import LoggingConnection
 
 from lib.config import config
 
@@ -14,7 +17,9 @@ class DB:
             # read the connection parameters
             params = config(section=self.config_section)
             # connect to the PostgreSQL server
-            self.conn = psycopg2.connect(**params)
+            self.conn = psycopg2.connect(connection_factory=LoggingConnection, **params)
+            logger = logging.getLogger(__name__)
+            self.conn.initialize(logger)
 
         except (Exception, psycopg2.DatabaseError) as error:
             print(error)
@@ -96,6 +101,7 @@ class DB:
             "UPDATE scheme SET version=4",
         )
         schemes[5] = (
+            """DROP TABLE IF EXISTS files""",
             """
             CREATE TABLE files (
                 id              SERIAL PRIMARY KEY,
@@ -109,6 +115,7 @@ class DB:
             "UPDATE scheme SET version=5",
         )
         schemes[6] = (
+            """DROP TABLE IF EXISTS requests""",
             """
             CREATE TABLE requests (
                 id              SERIAL PRIMARY KEY,
@@ -154,6 +161,7 @@ class DB:
             "UPDATE scheme SET version=12",
         )
         schemes[13] = (
+            """DROP TABLE IF EXISTS linked_revs""",
             """
             CREATE TABLE users (
                 id              SERIAL PRIMARY KEY,
@@ -174,6 +182,30 @@ class DB:
             """,
             "UPDATE scheme SET version=14",
         )
+        schemes[14] = (
+            "ALTER TABLE revisions ALTER COLUMN rev TYPE real USING rev::real",
+            "UPDATE scheme SET version=14",
+        )
+        schemes[15] = (
+            """DROP TABLE IF EXISTS fake_revs""",
+            """
+            CREATE TABLE fake_revs (
+                id              SERIAL PRIMARY KEY,
+                revision_id     INTEGER NOT NULL,
+                linked_id       INTEGER NOT NULL
+            )
+            """,
+            "create index revs_linked on fake_revs (revision_id,linked_id)",
+            "UPDATE scheme SET version=15",
+        )
+        schemes[16] = (
+            "ALTER TABLE revisions ADD COLUMN files_hash VARCHAR(40)",
+            "UPDATE scheme SET version=16",
+        )
+        schemes[17] = (
+            "ALTER TABLE linked_revs ADD COLUMN considered BOOLEAN DEFAULT FALSE",
+            "UPDATE scheme SET version=17",
+        )
         schema_version = self.schema_version()
         if (schema_version + 1) not in schemes:
             return