Module: Gitlab::Database::Migrations::ConstraintsHelpers

Includes:
LockRetriesHelpers, TimeoutHelpers
Included in:
Gitlab::Database::MigrationHelpers
Defined in:
lib/gitlab/database/migrations/constraints_helpers.rb

Constant Summary collapse

MAX_IDENTIFIER_NAME_LENGTH =

www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS

63

Class Method Summary collapse

Instance Method Summary collapse

Methods included from TimeoutHelpers

#disable_statement_timeout

Methods included from LockRetriesHelpers

#with_lock_retries

Class Method Details

.check_constraint_exists?(table, constraint_name, connection:) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 13

def self.check_constraint_exists?(table, constraint_name, connection:)
  # Constraint names are unique per table in Postgres, not per schema
  # Two tables can have constraints with the same name, so we filter by
  # the table name in addition to using the constraint_name

  check_sql = <<~SQL
    SELECT COUNT(*)
    FROM pg_catalog.pg_constraint con
      INNER JOIN pg_catalog.pg_class rel
        ON rel.oid = con.conrelid
      INNER JOIN pg_catalog.pg_namespace nsp
        ON nsp.oid = con.connamespace
    WHERE con.contype = 'c'
    AND con.conname = #{connection.quote(constraint_name)}
    AND nsp.nspname = #{connection.quote(connection.current_schema)}
    AND rel.relname = #{connection.quote(table)}
  SQL

  connection.select_value(check_sql.squish) > 0
end

Instance Method Details

#add_check_constraint(table, check, constraint_name, validate: true) ⇒ Object

Adds a check constraint to a table

This method is the generic helper for adding any check constraint More specialized helpers may use it (e.g. add_text_limit or add_not_null)

This method only requires minimal locking:

  • The constraint is added using NOT VALID This allows us to add the check constraint without validating it

  • The check will be enforced for new data (inserts) coming in

  • If ‘validate: true` the constraint is also validated Otherwise, validate_check_constraint() can be used at a later stage

  • Check comments on add_concurrent_foreign_key for more info

table - The table the constraint will be added to check - The check clause to add

e.g. 'char_length(name) <= 5' or 'store IS NOT NULL'

constraint_name - The name of the check constraint (otherwise auto-generated)

Should be unique per table (not per column)

validate - Whether to validate the constraint in this call



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 76

def add_check_constraint(table, check, constraint_name, validate: true)
  # Transactions would result in ALTER TABLE locks being held for the
  # duration of the transaction, defeating the purpose of this method.
  validate_not_in_transaction!(:add_check_constraint)

  validate_check_constraint_name!(constraint_name)

  if check_constraint_exists?(table, constraint_name)
    warning_message = <<~MESSAGE
      Check constraint was not created because it exists already
      (this may be due to an aborted migration or similar)
      table: #{table}, check: #{check}, constraint name: #{constraint_name}
    MESSAGE

    Gitlab::AppLogger.warn warning_message
  else
    # Only add the constraint without validating it
    # Even though it is fast, ADD CONSTRAINT requires an EXCLUSIVE lock
    # Use with_lock_retries to make sure that this operation
    # will not timeout on tables accessed by many processes
    with_lock_retries do
      execute <<~SQL
      ALTER TABLE #{table}
      ADD CONSTRAINT #{constraint_name}
      CHECK ( #{check} )
      NOT VALID;
      SQL
    end
  end

  validate_check_constraint(table, constraint_name) if validate
end

#add_not_null_constraint(table, column, constraint_name: nil, validate: true) ⇒ Object

Migration Helpers for managing not null constraints



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 213

def add_not_null_constraint(table, column, constraint_name: nil, validate: true)
  if column_is_nullable?(table, column)
    add_check_constraint(
      table,
      "#{column} IS NOT NULL",
      not_null_constraint_name(table, column, name: constraint_name),
      validate: validate
    )
  else
    warning_message = <<~MESSAGE
      NOT NULL check constraint was not created:
      column #{table}.#{column} is already defined as `NOT NULL`
    MESSAGE

    Gitlab::AppLogger.warn warning_message
  end
end

#add_text_limit(table, column, limit, constraint_name: nil, validate: true) ⇒ Object

Migration Helpers for adding limit to text columns



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 191

def add_text_limit(table, column, limit, constraint_name: nil, validate: true)
  add_check_constraint(
    table,
    "char_length(#{column}) <= #{limit}",
    text_limit_name(table, column, name: constraint_name),
    validate: validate
  )
end

#check_constraint_exists?(table, constraint_name) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 52

def check_constraint_exists?(table, constraint_name)
  ConstraintsHelpers.check_constraint_exists?(table, constraint_name, connection: connection)
end

#check_constraint_name(table, column, type) ⇒ Object

Returns the name for a check constraint

type:

  • Any value, as long as it is unique

  • Constraint names are unique per table in Postgres, and, additionally, we can have multiple check constraints over a column So we use the (table, column, type) triplet as a unique name

  • e.g. we use ‘max_length’ when adding checks for text limits

    or 'not_null' when adding a NOT NULL constraint



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 44

def check_constraint_name(table, column, type)
  identifier = "#{table}_#{column}_check_#{type}"
  # Check concurrent_foreign_key_name() for info on why we use a hash
  hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)

  "check_#{hashed_identifier}"
end

#check_not_null_constraint_exists?(table, column, constraint_name: nil) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 245

def check_not_null_constraint_exists?(table, column, constraint_name: nil)
  check_constraint_exists?(
    table,
    not_null_constraint_name(table, column, name: constraint_name)
  )
end

#check_text_limit_exists?(table, column, constraint_name: nil) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 208

def check_text_limit_exists?(table, column, constraint_name: nil)
  check_constraint_exists?(table, text_limit_name(table, column, name: constraint_name))
end

#copy_check_constraints(table, old, new, schema: nil) ⇒ Object

Copies all check constraints for the old column to the new column.

table - The table containing the columns. old - The old column. new - The new column. schema - The schema the table is defined for

If it is not provided, then the current_schema is used



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 147

def copy_check_constraints(table, old, new, schema: nil)
  raise 'copy_check_constraints can not be run inside a transaction' if transaction_open?

  raise "Column #{old} does not exist on #{table}" unless column_exists?(table, old)

  raise "Column #{new} does not exist on #{table}" unless column_exists?(table, new)

  table_with_schema = schema.present? ? "#{schema}.#{table}" : table

  check_constraints_for(table, old, schema: schema).each do |check_c|
    validate = !(check_c["constraint_def"].end_with? "NOT VALID")

    # Normalize:
    # - Old constraint definitions:
    #    '(char_length(entity_path) <= 5500)'
    # - Definitionss from pg_get_constraintdef(oid):
    #    'CHECK ((char_length(entity_path) <= 5500))'
    # - Definitions from pg_get_constraintdef(oid, pretty_bool):
    #    'CHECK (char_length(entity_path) <= 5500)'
    # - Not valid constraints: 'CHECK (...) NOT VALID'
    # to a single format that we can use:
    #    '(char_length(entity_path) <= 5500)'
    check_definition = check_c["constraint_def"]
                        .sub(/^\s*(CHECK)?\s*\({0,2}/, '(')
                        .sub(/\){0,2}\s*(NOT VALID)?\s*$/, ')')

    constraint_name = if check_definition == "(#{old} IS NOT NULL)"
                        not_null_constraint_name(table_with_schema, new)
                      elsif check_definition.start_with? "(char_length(#{old}) <="
                        text_limit_name(table_with_schema, new)
                      else
                        check_constraint_name(table_with_schema, new, 'copy_check_constraint')
                      end

    add_check_constraint(
      table_with_schema,
      check_definition.gsub(old.to_s, new.to_s),
      constraint_name,
      validate: validate
    )
  end
end

#drop_constraint(table_name, constraint_name, cascade: false) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 259

def drop_constraint(table_name, constraint_name, cascade: false)
  execute <<~SQL
    ALTER TABLE #{quote_table_name(table_name)} DROP CONSTRAINT #{quote_column_name(constraint_name)} #{cascade_statement(cascade)}
  SQL
end

#remove_check_constraint(table, constraint_name) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 123

def remove_check_constraint(table, constraint_name)
  # This is technically not necessary, but aligned with add_check_constraint
  # and allows us to continue use with_lock_retries here
  validate_not_in_transaction!(:remove_check_constraint)

  validate_check_constraint_name!(constraint_name)

  # DROP CONSTRAINT requires an EXCLUSIVE lock
  # Use with_lock_retries to make sure that this will not timeout
  with_lock_retries do
    execute <<-SQL
    ALTER TABLE #{table}
    DROP CONSTRAINT IF EXISTS #{constraint_name}
    SQL
  end
end

#remove_not_null_constraint(table, column, constraint_name: nil) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 238

def remove_not_null_constraint(table, column, constraint_name: nil)
  remove_check_constraint(
    table,
    not_null_constraint_name(table, column, name: constraint_name)
  )
end

#remove_text_limit(table, column, constraint_name: nil) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 204

def remove_text_limit(table, column, constraint_name: nil)
  remove_check_constraint(table, text_limit_name(table, column, name: constraint_name))
end

#rename_constraint(table_name, old_name, new_name) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 252

def rename_constraint(table_name, old_name, new_name)
  execute <<~SQL
    ALTER TABLE #{quote_table_name(table_name)}
    RENAME CONSTRAINT #{quote_column_name(old_name)} TO #{quote_column_name(new_name)}
  SQL
end

#switch_constraint_names(table_name, constraint_a, constraint_b) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 265

def switch_constraint_names(table_name, constraint_a, constraint_b)
  validate_not_in_transaction!(:switch_constraint_names)

  with_lock_retries do
    rename_constraint(table_name, constraint_a, :temp_name_for_renaming)
    rename_constraint(table_name, constraint_b, constraint_a)
    rename_constraint(table_name, :temp_name_for_renaming, constraint_b)
  end
end

#text_limit_name(table, column, name: nil) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 281

def text_limit_name(table, column, name: nil)
  name.presence || check_constraint_name(table, column, 'max_length')
end

#validate_check_constraint(table, constraint_name) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 109

def validate_check_constraint(table, constraint_name)
  validate_check_constraint_name!(constraint_name)

  unless check_constraint_exists?(table, constraint_name)
    raise missing_schema_object_message(table, "check constraint", constraint_name)
  end

  disable_statement_timeout do
    # VALIDATE CONSTRAINT only requires a SHARE UPDATE EXCLUSIVE LOCK
    # It only conflicts with other validations and creating indexes
    execute("ALTER TABLE #{table} VALIDATE CONSTRAINT #{constraint_name};")
  end
end

#validate_check_constraint_name!(constraint_name) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 275

def validate_check_constraint_name!(constraint_name)
  return unless constraint_name.to_s.length > MAX_IDENTIFIER_NAME_LENGTH

  raise "The maximum allowed constraint name is #{MAX_IDENTIFIER_NAME_LENGTH} characters"
end

#validate_not_null_constraint(table, column, constraint_name: nil) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 231

def validate_not_null_constraint(table, column, constraint_name: nil)
  validate_check_constraint(
    table,
    not_null_constraint_name(table, column, name: constraint_name)
  )
end

#validate_text_limit(table, column, constraint_name: nil) ⇒ Object 



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# File 'lib/gitlab/database/migrations/constraints_helpers.rb', line 200

def validate_text_limit(table, column, constraint_name: nil)
  validate_check_constraint(table, text_limit_name(table, column, name: constraint_name))
end