112 lines
3.9 KiB
Ruby
112 lines
3.9 KiB
Ruby
# frozen_string_literal: true
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#
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# Query a recursively defined namespace hierarchy using linear methods through
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# the traversal_ids attribute.
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#
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# Namespace is a nested hierarchy of one parent to many children. A search
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# using only the parent-child relationships is a slow operation. This process
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# was previously optimized using Postgresql recursive common table expressions
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# (CTE) with acceptable performance. However, it lead to slower than possible
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# performance, and resulted in complicated queries that were difficult to make
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# performant.
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#
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# Instead of searching the hierarchy recursively, we store a `traversal_ids`
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# attribute on each node. The `traversal_ids` is an ordered array of Namespace
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# IDs that define the traversal path from the root Namespace to the current
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# Namespace.
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#
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# For example, suppose we have the following Namespaces:
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#
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# GitLab (id: 1) > Engineering (id: 2) > Manage (id: 3) > Access (id: 4)
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#
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# Then `traversal_ids` for group "Access" is [1, 2, 3, 4]
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#
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# And we can match against other Namespace `traversal_ids` such that:
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#
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# - Ancestors are [1], [1, 2], [1, 2, 3]
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# - Descendants are [1, 2, 3, 4, *]
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# - Root is [1]
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# - Hierarchy is [1, *]
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#
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# Note that this search method works so long as the IDs are unique and the
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# traversal path is ordered from root to leaf nodes.
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#
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# We implement this in the database using Postgresql arrays, indexed by a
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# generalized inverted index (gin).
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module Namespaces
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module Traversal
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module Linear
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extend ActiveSupport::Concern
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UnboundedSearch = Class.new(StandardError)
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included do
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after_create :sync_traversal_ids, if: -> { sync_traversal_ids? }
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after_update :sync_traversal_ids, if: -> { sync_traversal_ids? && saved_change_to_parent_id? }
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scope :traversal_ids_contains, ->(ids) { where("traversal_ids @> (?)", ids) }
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end
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def sync_traversal_ids?
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Feature.enabled?(:sync_traversal_ids, root_ancestor, default_enabled: :yaml)
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end
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def use_traversal_ids?
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Feature.enabled?(:use_traversal_ids, root_ancestor, default_enabled: :yaml)
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end
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def self_and_descendants
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if use_traversal_ids?
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lineage(self)
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else
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super
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end
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end
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private
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# Update the traversal_ids for the full hierarchy.
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#
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# NOTE: self.traversal_ids will be stale. Reload for a fresh record.
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def sync_traversal_ids
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# Clear any previously memoized root_ancestor as our ancestors have changed.
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clear_memoization(:root_ancestor)
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Namespace::TraversalHierarchy.for_namespace(root_ancestor).sync_traversal_ids!
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end
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# Make sure we drop the STI `type = 'Group'` condition for better performance.
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# Logically equivalent so long as hierarchies remain homogeneous.
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def without_sti_condition
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self.class.unscope(where: :type)
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end
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# Search this namespace's lineage. Bound inclusively by top node.
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def lineage(top)
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raise UnboundedSearch.new('Must bound search by a top') unless top
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without_sti_condition
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.traversal_ids_contains(latest_traversal_ids(top))
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end
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# traversal_ids are a cached value.
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#
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# The traversal_ids value in a loaded object can become stale when compared
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# to the database value. For example, if you load a hierarchy and then move
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# a group, any previously loaded descendant objects will have out of date
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# traversal_ids.
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#
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# To solve this problem, we never depend on the object's traversal_ids
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# value. We always query the database first with a sub-select for the
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# latest traversal_ids.
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#
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# Note that ActiveRecord will cache query results. You can avoid this by
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# using `Model.uncached { ... }`
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def latest_traversal_ids(namespace = self)
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without_sti_condition.where('id = (?)', namespace)
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.select('traversal_ids as latest_traversal_ids')
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end
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end
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end
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end
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