Rewind IID on Ci::Pipelines

If no pipeline is created we currently have IID gap.
This is due to fact that we generate IID not on save,
but rather ahead of time. This results, us,
losing IIDs.

2 files changed, 49 insertions, 12 deletions

diff --git a/app/models/concerns/atomic_internal_id.rb b/app/models/concerns/atomic_internal_id.rb
index ab3d9e923c0..dc1735a7e48 100644
--- a/app/models/concerns/atomic_internal_id.rb
+++ b/app/models/concerns/atomic_internal_id.rb
@@ -53,6 +53,20 @@ module AtomicInternalId
 
         value
       end
+
+      define_method("reset_#{scope}_#{column}") do
+        if value = read_attribute(column)
+          scope_value = association(scope).reader
+          scope_attrs = { scope_value.class.table_name.singularize.to_sym => scope_value }
+          usage = self.class.table_name.to_sym
+
+          if InternalId.reset(self, scope_attrs, usage, value)
+            write_attribute(column, nil)
+          end
+        end
+
+        read_attribute(column)
+      end
     end
   end
 end
diff --git a/app/models/internal_id.rb b/app/models/internal_id.rb
index 3f2d368a3f2..401b94d36e5 100644
--- a/app/models/internal_id.rb
+++ b/app/models/internal_id.rb
@@ -55,7 +55,8 @@ class InternalId < ApplicationRecord
     def track_greatest(subject, scope, usage, new_value, init)
       return new_value unless available?
 
-      InternalIdGenerator.new(subject, scope, usage, init).track_greatest(new_value)
+      InternalIdGenerator.new(subject, scope, usage)
+        .track_greatest(init, new_value)
     end
 
     def generate_next(subject, scope, usage, init)
@@ -63,7 +64,15 @@ class InternalId < ApplicationRecord
       # This can be the case in other (unrelated) migration specs
       return (init.call(subject) || 0) + 1 unless available?
 
-      InternalIdGenerator.new(subject, scope, usage, init).generate
+      InternalIdGenerator.new(subject, scope, usage)
+        .generate(init)
+    end
+
+    def reset(subject, scope, usage, value)
+      return false unless available?
+
+      InternalIdGenerator.new(subject, scope, usage)
+        .reset(value)
     end
 
     # Flushing records is generally safe in a sense that those
@@ -103,14 +112,11 @@ class InternalId < ApplicationRecord
     # subject: The instance we're generating an internal id for. Gets passed to init if called.
     # scope: Attributes that define the scope for id generation.
     # usage: Symbol to define the usage of the internal id, see InternalId.usages
-    # init: Block that gets called to initialize InternalId record if not present
-    #       Make sure to not throw exceptions in the absence of records (if this is expected).
-    attr_reader :subject, :scope, :init, :scope_attrs, :usage
+    attr_reader :subject, :scope, :scope_attrs, :usage
 
-    def initialize(subject, scope, usage, init)
+    def initialize(subject, scope, usage)
       @subject = subject
       @scope = scope
-      @init = init
       @usage = usage
 
       raise ArgumentError, 'Scope is not well-defined, need at least one column for scope (given: 0)' if scope.empty?
@@ -121,23 +127,40 @@ class InternalId < ApplicationRecord
     end
 
     # Generates next internal id and returns it
-    def generate
+    # init: Block that gets called to initialize InternalId record if not present
+    #       Make sure to not throw exceptions in the absence of records (if this is expected).
+    def generate(init)
       subject.transaction do
         # Create a record in internal_ids if one does not yet exist
         # and increment its last value
         #
         # Note this will acquire a ROW SHARE lock on the InternalId record
-        (lookup || create_record).increment_and_save!
+        (lookup || create_record(init)).increment_and_save!
       end
     end
 
+    # Reset tries to rewind to `value-1`. This will only succeed,
+    # if `value` stored in database is equal to `last_value`.
+    # value: The expected last_value to decrement
+    def reset(value)
+      return false unless value
+
+      updated =
+        InternalId
+          .where(**scope, usage: usage_value)
+          .where(last_value: value)
+          .update_all('last_value = last_value - 1')
+
+      updated > 0
+    end
+
     # Create a record in internal_ids if one does not yet exist
     # and set its new_value if it is higher than the current last_value
     #
     # Note this will acquire a ROW SHARE lock on the InternalId record
-    def track_greatest(new_value)
+    def track_greatest(init, new_value)
       subject.transaction do
-        (lookup || create_record).track_greatest_and_save!(new_value)
+        (lookup || create_record(init)).track_greatest_and_save!(new_value)
       end
     end
 
@@ -158,7 +181,7 @@ class InternalId < ApplicationRecord
     # was faster in doing this, we'll realize once we hit the unique key constraint
     # violation. We can safely roll-back the nested transaction and perform
     # a lookup instead to retrieve the record.
-    def create_record
+    def create_record(init)
       subject.transaction(requires_new: true) do
         InternalId.create!(
           **scope,