From 896c0bdbfb1a83ff5a7d0a755ac249ac2a895798 Mon Sep 17 00:00:00 2001 From: Zeger-Jan van de Weg Date: Mon, 3 Dec 2018 14:49:58 +0100 Subject: Allow public forks to be deduplicated When a project is forked, the new repository used to be a deep copy of everything stored on disk by leveraging `git clone`. This works well, and makes isolation between repository easy. However, the clone is at the start 100% the same as the origin repository. And in the case of the objects in the object directory, this is almost always going to be a lot of duplication. Object Pools are a way to create a third repository that essentially only exists for its 'objects' subdirectory. This third repository's object directory will be set as alternate location for objects. This means that in the case an object is missing in the local repository, git will look in another location. This other location is the object pool repository. When Git performs garbage collection, it's smart enough to check the alternate location. When objects are duplicated, it will allow git to throw one copy away. This copy is on the local repository, where to pool remains as is. These pools have an origin location, which for now will always be a repository that itself is not a fork. When the root of a fork network is forked by a user, the fork still clones the full repository. Async, the pool repository will be created. Either one of these processes can be done earlier than the other. To handle this race condition, the Join ObjectPool operation is idempotent. Given its idempotent, we can schedule it twice, with the same effect. To accommodate the holding of state two migrations have been added. 1. Added a state column to the pool_repositories column. This column is managed by the state machine, allowing for hooks on transitions. 2. pool_repositories now has a source_project_id. This column in convenient to have for multiple reasons: it has a unique index allowing the database to handle race conditions when creating a new record. Also, it's nice to know who the host is. As that's a short link to the fork networks root. Object pools are only available for public project, which use hashed storage and when forking from the root of the fork network. (That is, the project being forked from itself isn't a fork) In this commit message I use both ObjectPool and Pool repositories, which are alike, but different from each other. ObjectPool refers to whatever is on the disk stored and managed by Gitaly. PoolRepository is the record in the database. --- .../20181128123704_add_state_to_pool_repository.rb | 19 +++++++++++++++++++ db/schema.rb | 4 ++++ 2 files changed, 23 insertions(+) create mode 100644 db/migrate/20181128123704_add_state_to_pool_repository.rb (limited to 'db') diff --git a/db/migrate/20181128123704_add_state_to_pool_repository.rb b/db/migrate/20181128123704_add_state_to_pool_repository.rb new file mode 100644 index 00000000000..714232ede56 --- /dev/null +++ b/db/migrate/20181128123704_add_state_to_pool_repository.rb @@ -0,0 +1,19 @@ +# frozen_string_literal: true + +class AddStateToPoolRepository < ActiveRecord::Migration[5.0] + include Gitlab::Database::MigrationHelpers + + DOWNTIME = false + + # Given the table is empty, and the non concurrent methods are chosen so + # the transactions don't have to be disabled + # rubocop: disable Migration/AddConcurrentForeignKey, Migration/AddIndex + def change + add_column(:pool_repositories, :state, :string, null: true) + + add_column :pool_repositories, :source_project_id, :integer + add_index :pool_repositories, :source_project_id, unique: true + add_foreign_key :pool_repositories, :projects, column: :source_project_id, on_delete: :nullify + end + # rubocop: enable Migration/AddConcurrentForeignKey, Migration/AddIndex +end diff --git a/db/schema.rb b/db/schema.rb index d7124100621..ff2dde3243c 100644 --- a/db/schema.rb +++ b/db/schema.rb @@ -1512,8 +1512,11 @@ ActiveRecord::Schema.define(version: 20181203002526) do create_table "pool_repositories", id: :bigserial, force: :cascade do |t| t.integer "shard_id", null: false t.string "disk_path" + t.string "state" + t.integer "source_project_id" t.index ["disk_path"], name: "index_pool_repositories_on_disk_path", unique: true, using: :btree t.index ["shard_id"], name: "index_pool_repositories_on_shard_id", using: :btree + t.index ["source_project_id"], name: "index_pool_repositories_on_source_project_id", unique: true, using: :btree end create_table "programming_languages", force: :cascade do |t| @@ -2393,6 +2396,7 @@ ActiveRecord::Schema.define(version: 20181203002526) do add_foreign_key "oauth_openid_requests", "oauth_access_grants", column: "access_grant_id", name: "fk_oauth_openid_requests_oauth_access_grants_access_grant_id" add_foreign_key "pages_domains", "projects", name: "fk_ea2f6dfc6f", on_delete: :cascade add_foreign_key "personal_access_tokens", "users" + add_foreign_key "pool_repositories", "projects", column: "source_project_id", on_delete: :nullify add_foreign_key "pool_repositories", "shards", on_delete: :restrict add_foreign_key "project_authorizations", "projects", on_delete: :cascade add_foreign_key "project_authorizations", "users", on_delete: :cascade -- cgit v1.2.3