Add a module to handle deleting data

This, along with the way of specifying which branches are processed is a way
to manage the data stored within the Guix Data Service.

This only goes so far, it doesn't delete derivations, but it does delete some
of the information related to a revision.

Makefile.am

@@ -70,6 +70,7 @@ SOURCES =									\
   guix-data-service/comparison.scm						\
   guix-data-service/config.scm							\
   guix-data-service/database.scm						\
+  guix-data-service/data-deletion.scm						\
   guix-data-service/jobs.scm							\
   guix-data-service/jobs/load-new-guix-revision.scm				\
   guix-data-service/model/build-server.scm					\

guix-data-service/data-deletion.scm

@@ -0,0 +1,165 @@
+;;; Guix Data Service -- Information about Guix over time
+;;; Copyright © 2020 Christopher Baines <mail@cbaines.net>
+;;;
+;;; This program is free software: you can redistribute it and/or
+;;; modify it under the terms of the GNU Affero General Public License
+;;; as published by the Free Software Foundation, either version 3 of
+;;; the License, or (at your option) any later version.
+;;;
+;;; This program is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; Affero General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Affero General Public
+;;; License along with this program.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+(define-module (guix-data-service data-deletion)
+  #:use-module (squee)
+  #:use-module (guix-data-service database)
+  #:export (delete-data-for-branch))
+
+(define (delete-data-for-branch conn git-repository-id branch-name)
+  (define commits
+    (map car
+         (exec-query conn
+                     "
+SELECT commit
+FROM git_branches
+WHERE git_repository_id = $1 AND name = $2"
+                     (list (number->string git-repository-id)
+                           branch-name))))
+
+
+  (with-postgresql-transaction
+   conn
+   (lambda (conn)
+     (exec-query
+      conn
+      (simple-format
+       #f
+       "
+DELETE FROM git_branches
+WHERE git_repository_id = ~A AND
+  name = '~A' AND
+  commit IN (~A)"
+       git-repository-id
+       branch-name
+       (string-join
+        (map (lambda (commit)
+               (string-append "'" commit "'"))
+             commits)
+        ", ")))
+
+     (for-each
+      (lambda (table)
+        (exec-query
+         conn
+         (simple-format
+          #f
+          "
+DELETE FROM ~A
+WHERE branch_name = $1 AND git_repository_id = $2"
+          table)
+         (list branch-name
+               (number->string git-repository-id))))
+      '("package_versions_by_guix_revision_range"
+        "package_derivations_by_guix_revision_range"))
+
+     (for-each
+      (lambda (table)
+        (exec-query
+         conn
+         (string-append
+          "
+DELETE FROM " table "
+WHERE job_id IN (
+  SELECT id
+  FROM load_new_guix_revision_jobs
+  WHERE git_repository_id = " (number->string git-repository-id) " AND
+    commit IN ("
+  (string-join
+   (map (lambda (commit)
+          (string-append "'" commit "'"))
+        commits)
+   ", ")
+  ")
+)")))
+      '("load_new_guix_revision_job_events"
+        "load_new_guix_revision_job_logs"))
+
+     (exec-query
+      conn
+      (string-append
+       "
+DELETE FROM load_new_guix_revision_jobs
+WHERE git_repository_id = " (number->string git-repository-id) " AND
+  commit IN ("
+      (string-join
+       (map (lambda (commit)
+              (string-append "'" commit "'"))
+            commits)
+       ", ")
+      ")"))
+
+     (let ((guix-revision-ids
+            (map
+             car
+             (exec-query
+              conn
+              (string-append
+               "
+SELECT guix_revisions.id
+FROM (VALUES "
+               (string-join
+                (map (lambda (commit)
+                       (string-append "('" commit "')"))
+                     commits)
+                ", ")
+               ") AS commits
+INNER JOIN guix_revisions
+  ON guix_revisions.commit = commits.column1
+WHERE guix_revisions.git_repository_id = "
+               (number->string git-repository-id) " AND
+  commits.column1 NOT IN (
+    SELECT commit
+    FROM git_branches
+)")))))
+
+       (unless (null? guix-revision-ids)
+         (for-each
+          (lambda (table)
+            (exec-query
+             conn
+             (simple-format
+              #f
+              "
+DELETE FROM ~A WHERE ~A IN (VALUES ~A)"
+              table
+              (if (string=? table
+                            "guix_revision_package_derivations")
+                  "revision_id"
+                  "guix_revision_id")
+              (string-join
+               (map (lambda (guix-revision-id)
+                      (string-append "(" guix-revision-id ")"))
+                    guix-revision-ids)
+               ", "))))
+          '("channel_instances"
+            "guix_revision_channel_news_entries"
+            "guix_revision_lint_checkers"
+            "guix_revision_lint_warnings"
+            "guix_revision_package_derivations"
+            "guix_revision_system_test_derivations"))
+
+         (exec-query
+          conn
+          (string-append
+           "
+DELETE FROM guix_revisions
+WHERE id IN ("
+           (string-join guix-revision-ids ", ")
+           ")")))))))
+
+(with-postgresql-connection "foo" (lambda (conn) (for-each (lambda (branch-name) (delete-data-for-branch conn 1 branch-name)) (map car (exec-query conn "SELECT DISTINCT name FROM git_branches WHERE git_repository_id = 1 AND name != 'master'")))))