Module: Gitlab::Database::PartitioningMigrationHelpers::ForeignKeyHelpers

Includes:
SchemaHelpers
Included in:
Gitlab::Database::PartitioningMigrationHelpers
Defined in:
lib/gitlab/database/partitioning_migration_helpers/foreign_key_helpers.rb

Constant Summary collapse

ERROR_SCOPE = 
'foreign keys'

Instance Method Summary collapse

Methods included from SchemaHelpers

#assert_not_in_transaction_block, #create_comment, #create_trigger, #create_trigger_function, #drop_function, #drop_trigger, #function_exists?, #object_name, #tmp_table_name, #trigger_exists?, #with_lock_retries

Instance Method Details

#add_concurrent_partitioned_foreign_key(source, target, column:, on_delete: :cascade, name: nil) ⇒ Object

Adds a foreign key with only minimal locking on the tables involved.

In concept it works similarly to add_concurrent_foreign_key, but we have to add a special helper for partitioned tables for the following reasons:

  • add_concurrent_foreign_key sets the constraint to `NOT VALID` before validating it

  • Setting an FK to NOT VALID is not supported currently in Postgres (up to PG13)

  • Also, PostgreSQL will currently ignore NOT VALID constraints on partitions when adding a valid FK to the partitioned table, so they have to also be validated before we can add the final FK.

Solution:

  • Add the foreign key first to each partition by using add_concurrent_foreign_key and validating it

  • Once all partitions have a foreign key, add it also to the partitioned table (there will be no need for a validation at that level)

For those reasons, this method does not include an option to delay the validation, we have to force validate: true.

source - The source (partitioned) table containing the foreign key. target - The target table the key points to. column - The name of the column to create the foreign key on. on_delete - The action to perform when associated data is removed,

defaults to "CASCADE".

name - The name of the foreign key.


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# File 'lib/gitlab/database/partitioning_migration_helpers/foreign_key_helpers.rb', line 36

def add_concurrent_partitioned_foreign_key(source, target, column:, on_delete: :cascade, name: nil)
  assert_not_in_transaction_block(scope: ERROR_SCOPE)

  partition_options = {
    column: column,
    on_delete: on_delete,

    # We'll use the same FK name for all partitions and match it to
    # the name used for the partitioned table to follow the convention
    # used by PostgreSQL when adding FKs to new partitions
    name: name.presence || concurrent_partitioned_foreign_key_name(source, column),

    # Force the FK validation to true for partitions (and the partitioned table)
    validate: true
  }

  if foreign_key_exists?(source, target, **partition_options)
    warning_message = "Foreign key not created because it exists already " \
      "(this may be due to an aborted migration or similar): " \
      "source: #{source}, target: #{target}, column: #{partition_options[:column]}, "\
      "name: #{partition_options[:name]}, on_delete: #{partition_options[:on_delete]}"

    Gitlab::AppLogger.warn warning_message

    return
  end

  partitioned_table = find_partitioned_table(source)

  partitioned_table.postgres_partitions.order(:name).each do |partition|
    add_concurrent_foreign_key(partition.identifier, target, **partition_options)
  end

  with_lock_retries do
    add_foreign_key(source, target, **partition_options)
  end
end

#concurrent_partitioned_foreign_key_name(table, column, prefix: 'fk_rails_') ⇒ Object

Returns the name for a concurrent partitioned foreign key.

Similar to concurrent_foreign_key_name (Gitlab::Database::MigrationHelpers) we just keep a separate method in case we want a different behavior for partitioned tables


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# File 'lib/gitlab/database/partitioning_migration_helpers/foreign_key_helpers.rb', line 80

def concurrent_partitioned_foreign_key_name(table, column, prefix: 'fk_rails_')
  identifier = "#{table}_#{column}_fk"
  hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)

  "#{prefix}#{hashed_identifier}"
end