Features and Improvements in ArangoDB 2.2

The following list shows in detail which features have been added or improved in ArangoDB 2.2. ArangoDB 2.2 also contains several bugfixes that are not listed here.

AQL improvements

Data modification AQL queries

Up to including version 2.1, AQL supported data retrieval operations only. Starting with ArangoDB version 2.2, AQL also supports the following data modification operations:

  • INSERT: insert new documents into a collection
  • UPDATE: partially update existing documents in a collection
  • REPLACE: completely replace existing documents in a collection
  • REMOVE: remove existing documents from a collection

Data-modification operations are normally combined with other AQL statements such as FOR loops and FILTER conditions to determine the set of documents to operate on. For example, the following query will find all documents in collection users that match a specific condition and set their status variable to inactive:

FOR u IN users
  FILTER u.status == 'not active'
  UPDATE u WITH { status: 'inactive' } IN users

The following query copies all documents from collection users into collection backup:

FOR u IN users
  INSERT u IN backup

And this query removes documents from collection backup:

FOR doc IN backup
  FILTER doc.lastModified < DATE_NOW() - 3600
  REMOVE doc IN backup

For more information on data-modification queries, please refer to Data modification queries.

Updatable variables

Previously, the value of a variable assigned in an AQL query with the LET keyword was not updatable in an AQL query. This prevented statements like the following from being executable:

LET sum = 0
FOR v IN values
  SORT v.year
  LET sum = sum + v.value
  RETURN { year: v.year, value: v.value, sum: sum }

Other AQL improvements

  • added AQL TRANSLATE function

    This function can be used to perform lookups from static objects, e.g.

    LET countryNames = { US: "United States", UK: "United Kingdom", FR: "France" }
    RETURN TRANSLATE("FR", countryNames) 
    LET lookup = { foo: "foo-replacement", bar: "bar-replacement", baz: "baz-replacement" }
    RETURN TRANSLATE("foobar", lookup, "not contained!")

Write-ahead log

All write operations in an ArangoDB server will now be automatically logged in the server’s write-ahead log. The write-ahead log is a set of append-only logfiles, and it is used in case of a crash recovery and for replication.

Data from the write-ahead log will eventually be moved into the journals or datafiles of collections, allowing the server to remove older write-ahead logfiles.

Cross-collection transactions in ArangoDB should benefit considerably by this change, as less writes than in previous versions are required to ensure the data of multiple collections are atomically and durably committed. All data-modifying operations inside transactions (insert, update, remove) will write their operations into the write-ahead log directly now. In previous versions, such operations were buffered until the commit or rollback occurred. Transactions with multiple operations should therefore require less physical memory than in previous versions of ArangoDB.

The data in the write-ahead log can also be used in the replication context. In previous versions of ArangoDB, replicating from a master required turning on a special replication logger on the master. The replication logger caused an extra write operation into the _replication system collection for each actual write operation. This extra write is now superfluous. Instead, slaves can read directly from the master’s write-ahead log to get informed about most recent data changes. This removes the need to store data-modification operations in the _replication collection altogether.

The introduction of the write-ahead log also removes the need to configure and start the replication logger on a master. Though the replication logger object is still available in ArangoDB 2.2 to ensure API compatibility, starting, stopping, or configuring it will have no effect.

Performance improvements

  • Removed sorting of attribute names when in collection shaper

    In previous versions of ArangoDB, adding a document with previously not-used attribute names caused a full sort of all attribute names used in the collection. The sorting was done to ensure fast comparisons of attribute names in some rare edge cases, but it considerably slowed down inserts into collections with many different or even unique attribute names.

  • Specialized primary index implementation to allow faster hash table rebuilding and reduce lookups in datafiles for the actual value of _key. This also reduces the amount of random memory accesses for primary index inserts.

  • Reclamation of index memory when deleting last document in collection

    Deleting documents from a collection did not lead to index sizes being reduced. Instead, the index memory was kept allocated and re-used later when a collection was refilled with new documents. Now, index memory of primary indexes and hash indexes is reclaimed instantly when the last document in a collection is removed.

  • Prevent buffering of long print results in arangosh’s and arangod’s print command

    This change will emit buffered intermediate print results and discard the output buffer to quickly deliver print results to the user, and to prevent constructing very large buffers for large results.

Miscellaneous improvements

  • Added insert method as an alias for save. Documents can now be inserted into a collection using either method:

    db.test.save({ foo: "bar" }); 
    db.test.insert({ foo: "bar" }); 
  • Cleanup of options for data-modification operations

    Many of the data-modification operations had signatures with many optional bool parameters, e.g.:

    db.test.update("foo", { bar: "baz" }, true, true, true)
    db.test.replace("foo", { bar: "baz" }, true, true)
    db.test.remove("foo", true, true)
    db.test.save({ bar: "baz" }, true)

    Such long parameter lists were unintuitive and hard to use when only one of the optional parameters should have been set.

    To make the APIs more usable, the operations now understand the following alternative signature:

    collection.update(key, update-document, options)
    collection.replace(key, replacement-document, options)
    collection.remove(key, options)
    collection.save(document, options)


    db.test.update("foo", { bar: "baz" }, { overwrite: true, keepNull: true, waitForSync: true })
    db.test.replace("foo", { bar: "baz" }, { overwrite: true, waitForSync: true })
    db.test.remove("foo", { overwrite: true, waitForSync: true })
    db.test.save({ bar: "baz" }, { waitForSync: true })
  • Added --overwrite option to arangoimp

    This allows removing all documents in a collection before importing into it using arangoimp.

  • Honor startup option --server.disable-statistics when deciding whether or not to start periodic statistics collection jobs

    Previously, the statistics collection jobs were started even if the server was started with the --server.disable-statistics flag being set to true. Now if the option is set to true, no statistics will be collected on the server.

  • Disallow storing of JavaScript objects that contain JavaScript native objects of type Date, Function, RegExp or External, e.g.

    db.test.save({ foo: /bar/ });
    db.test.save({ foo: new Date() });

    This will now print

    Error: <data> cannot be converted into JSON shape: could not shape document

    Previously, objects of these types were silently converted into an empty object (i.e. { }) and no warning was issued.

    To store such objects in a collection, explicitly convert them into strings like this:

    db.test.save({ foo: String(/bar/) });
    db.test.save({ foo: String(new Date()) });

Removed features

MRuby integration for arangod

ArangoDB had an experimental MRuby integration in some of the publish builds. This wasn’t continuously developed, and so it has been removed in ArangoDB 2.2.

This change has led to the following startup options being superfluous:

  • --ruby.gc-interval
  • --ruby.action-directory
  • --ruby.modules-path
  • --ruby.startup-directory

Specifying these startup options will do nothing in ArangoDB 2.2, so using these options should be avoided from now on as they might be removed in a future version of ArangoDB.

Removed startup options

The following startup options have been removed in ArangoDB 2.2. Specifying them in the server’s configuration file will not produce an error to make migration easier. Still, usage of these options should be avoided as they will not have any effect and might fully be removed in a future version of ArangoDB:

  • --database.remove-on-drop
  • --database.force-sync-properties
  • --random.no-seed
  • --ruby.gc-interval
  • --ruby.action-directory
  • --ruby.modules-path
  • --ruby.startup-directory
  • --server.disable-replication-logger

Multi Collection Graphs

ArangoDB is a multi model database with native graph support. In version 2.2 the features for graphs have been improved by integration of a new graph module. All graphs created with the old module are automatically migrated into the new module but can still be used by the old module.

New graph module

Up to including version 2.1, ArangoDB offered a module for graphs and graph operations. This module allowed you to use exactly one edge collection together with one vertex collection in a graph. With ArangoDB version 2.2 this graph module is deprecated and a new graph module is offered. This new module allows to combine an arbitrary number of vertex collections and edge collections in the same graph. For each edge collection a list of collections containing source vertices and a list of collections containing target vertices can be defined. If an edge is stored ArangoDB checks if this edge is valid in this collection. Furthermore if a vertex is removed from one of the collections all connected edges will be removed as well, giving the guarantee of no loose ends in the graphs. The layout of the graph can be modified at runtime by adding or removing collections and changing the definitions for edge collections. All operations on the graph level are transactional by default.

Graphs in AQL

Multi collection graphs have been added to AQL as well. Basic functionality (getting vertices, edges, neighbors) can be executed using the entire graph. Also more advanced features like shortest path calculations, characteristic factors of the graph or traversals have been integrated into AQL. For these functions all graphs created with the graph module can be used.