ArcadeDB Manual

ArcadeDB is the new generation of DBMS that runs on pretty much every hardware/software configuration. ArcadeDB is Multi-Model, that means it can work with graphs, documents and other forms of data.

ArcadeDB is written in LLJ ("Low-Level-Java"), that means it’s written in Java (Java8+), but without using high-level API. The result is that ArcadeDB does not allocate many objects at run-time on the Heap, so the Garbage Collection doesn’t do much. At the same time, it’s still able to run on pretty much every sw/hw configuration and leverage of the hyper optimized Java Virtual Machine*. Furthermore, the kernel is built to be efficient on multi-core CPUs by using novel Mechanical Sympathy techniques.

ArcadeDB is a Native Graph Database:

ArcadeDB was born on the cloud. Even though you can run ArcadeDB as embedded and in an on-premise setup, you can spin an ArcadeDB server/cluster in a few seconds with Docker, Kubernetes, Amazon AWS (coming soon) and Microsoft Azure consoles (coming soon).

ArcadeDB Community Edition is really FREE for any purpose because released under Apache 2.0 license. We love knowing about your project with ArcadeDB and any contributions back to the Open Community (reports, patches, test cases, documentations, etc) are welcome.

Which is more likely to have better quality? A DBMS created and tested by a handful of developers or one tested by over 100,000 developers globally? When code is public, everyone can scrutinize, test, report and resolve issues. All things Open Source move faster compared to the proprietary world.

The ArcadeDB engine supports Graph, Document, Key/Value, and Time-Series models, so you can use ArcadeDB as a replacement for a product in any of these categories. However, the main reason why users choose ArcadeDB is because of its true Multi-Model DBMS abilities, which combine all the features of the four models into the core. These abilities are not just interfaces to the database engine, but rather the engine itself was built to support all four models. This is also the main difference to other multi-model DBMSs, as they implement an additional layer with an API, which mimics additional models. However, under the hood, they’re truly only one model, therefore they are limited in speed and scalability.

You can run ArcadeDB in the following ways:

To reach the best performance, use ArcadeDB in embedded mode to reach 2 Million insertions per second on common hardware. If you need to scale up with the queries, run a HA configuration with at least 3 servers, with a load balancer in front. Run ArcadeDB with Kubernetes to have an automatic setup of servers in HA with a load balancer upfront.

This mode is possible only if your application is running in a JVM* (Java* Virtual Machine). In this configuration ArcadeDB runs in the same JVM of your application. In this way you completely avoid the client/server communication cost (TCP/IP, marshalling/unmarshalling, etc.) If the JVM that hosts your application crashes, then also ArcadeDB crashes, but don’t worry, ArcadeDB uses a WAL to recover partially committed transactions. Your data is safe.

This is the classic way people use a DBMS, like with Relational Databases. The ArcadeDB server exposes HTTP/JSON API, so you can connect to ArcadeDB from any language without even using drivers. Take a look at the driver chapter for more information.

You can spin up as many ArcadeDB servers you want to have a HA setup and scale up with queries that can be executed on any servers. ArcadeDB uses a RAFT based election system to guarantee the consistency of the database. For more information look at High Availability.

A record is the smallest unit you can load from and store in the database. Records come in three types:

Documents are softly typed and are defined by schema types, but you can also use them in a schema-less mode too. Documents handle fields in a flexible manner. You can easily import and export them in JSON format. For example,

In Graph databases the vertices (also named vertexes), or nodes represent the main entity that holds the information. It can be a Patient, a Company or a Product. Vertices are themselves documents with some additional features. This means they can contain embedded records and arbitrary properties exactly like documents. Vertices are connected with other vertices through Edges.

An Edge, or Arc, is the connection between two vertices. Edges can be unidirectional and bidirectional. One edge can only connect two vertices.

For more information on connecting vertices in general, see Relationships below.

When ArcadeDB generates a record, it auto-assigns a unique identifier called a Record ID, RID for short. The syntax for the RID is the pound sign with the bucket identifier, colon, and the position like so:

#<bucket-identifier>:<record-position>.

#-1:-1 is a null RID.

Each Record ID is immutable, universal, and is never reused. Additionally, records can be accessed directly through their RIDs at O(1) complexity which means the query speed is constant, unaffected by database size. For this reason, you don’t need to create a field to serve as the primary key as you do in Relational databases.

The concept of the Type is taken from the Object Oriented Programming paradigm, sometimes as 'Class'. In ArcadeDB, types define records. It is closest to the concept of a 'Table' in Relational databases and a 'Class' in an Object Database.

Types can be schema-less, schema-full, or a mix. They can inherit from other types, creating a tree of types. Inheritance, in this context, means that a subtype extends a parent type, inheriting all of its attributes.

Each type has its own buckets (data files). A type can support multiple buckets. When you execute a query against a type, it automatically fetches from all the buckets that are part of the type. When you create a new record, ArcadeDB selects the bucket to store it in using a configurable strategy.

As a default, ArcadeDB creates as many buckets per type as many cores (processors) the host machine has. In this, CRUD operations can go full speed in parallel with zero contention between CPUs and/or COREs. Having many buckets per type means having more files at file system level. Check if your Operative System has any limitation with the number of files supported and opened at the same time (ulimit for Unix-like systems).

Where types provide you with a logical framework for organizing data, buckets provide physical or in-memory space in which ArcadeDB actually stores the data. Each bucket is one file at file system level. It is comparable to the "collection" in Document databases, the "table" in Relational databases and the "cluster" in OrientDB. You can have up to 2,147,483,648 buckets in a database.

A bucket can only be part of one type. This means two types can not share the same bucket.

When you create a new type, the CREATE TYPE statement automatically creates the physical buckets (files) that serve as the default location in which to store data for that type. ArcadeDB forms the bucket names by using the type name + underscore + a sequential number starting from 0. For example, the first bucket for the type Beer will be Beer_0 and the correspondent file in the file system will be Beer_0.31.65536.bucket. ArcadeDB creates additional buckets for each type, (one for each CPU core on the server), to improve performance of parallelism.

The combination of types and buckets is very powerful and has a number of use cases. In most case, you can work with Types and you will be fine. But if you are able to split your database into multiple buckets, you could address a specific bucket based instead of the entire Type. By wisely using the buckets to divide your database in a way that help you with the retrieval means zero or less use of indexes. Indexes slow down insertion and take space on disk and RAM. In most cases you need indexes to speed up your queries, but in some use cases you could totally or partially avoid using indexes and still having good performance on queries.

Consider an example where you create a type Invoice, with one bucket per year. Invoice_2015 and Invoice_2016. You can query all invoices using the type as a target with the SELECT statement.

In addition to this, you can filter the result set by the year. The type Invoice includes a year field, you can filter it through the WHERE clause.

You can also query specific records from a single bucket. By splitting the type Invoice across multiple buckets, (that is, one per year in our example), you can optimize the query by narrowing the potential result set.

By using the explicit bucket instead of the logical type, this query runs significantly faster, because ArcadeDB can narrow the search to the targeted bucket. No index is needed on the year, because all the invoices for year 2016 will be stored in the bucket Invoice_2016 by the application.

Like with the example above, we could split our records by location creating one bucket per location. Example:

Here we are using the graph model by creating a vertex type, but it’s the same with documents. Use CREATE DOCUMENT TYPE instead.

Now in your application store the vertices or documents in the right bucket, based on the location of such customer. You can use any API and set the bucket. If you’re using SQL, this is the way you can insert a new Customer into a specific bucket.

Since a bucket can only be part of one type, when you use the bucket notation with SQL, the type is inferred from the bucket, "Customer" in this case.

When you’re looking for customers based in Europe, you could execute this query:

You can go even more specific by creating a bucket per country, not just for continent, and query from that bucket. Example:

Now get all the customers that live in Italy.

You can also specify a list of buckets in your query. This is the query to retrieve both Italian and Spanish customers.

ArcadeDB supports two kinds of relationships: referenced and embedded. It can manage relationships in a schema-full or schema-less scenario.

In Relational databases, tables are linked through JOIN commands, which can prove costly on computing resources. ArcadeDB manages relationships natively without computing `JOIN’s by storing direct links to the target objects of the relationship. This boosts the load speed for the entire graph of connected objects, such as in Graph and Object database systems.

Example

When using Embedded relationships, ArcadeDB stores the relationship within the record that embeds it. These relationships are stronger than Reference relationships. You can represent it as a UML Composition relationship.

Embedded records do not have their own RID, given that you can’t directly reference it through other records. It is only accessible through the container record.

In the event that you delete the container record, the embedded record is also deleted. For example,

Here,record A contains the entirety of record B in the property address. You can reach record B only by traversing the container record. For example,

ArcadeDB expresses relationships of these kinds using the EMBEDDED type.

ArcadeDB expresses relationships of these kinds using a list or a map of links, such as:

In ArcadeDB, all Edges in the Graph model are bidirectional. This differs from the Document model, where relationships are always unidirectional, requiring the developer to maintain data integrity. In addition, ArcadeDB automatically maintains the consistency of all bidirectional relationships.

Each server or Java VM can handle multiple database instances, but the database name must be unique.

ArcadeDB uses its own URL format, of engine and database name as <engine>:<db-name>. The embedded engine is the default and can be omitted. To open a database on the local file system you can use directly the path as URL.

You must always close the database once you finish working on it.

A transaction comprises a unit of work performed within a database management system (or similar system) against a database, and treated in a coherent and reliable way independent of other transactions. Transactions in a database environment have two main purposes:

A database transaction, by definition, must be atomic, consistent, isolated and durable. Database practitioners often refer to these properties of database transactions using the acronym ACID). - Wikipedia

ArcadeDB is an ACID compliant DBMS.

"Atomicity requires that each transaction is 'all or nothing': if one part of the transaction fails, the entire transaction fails, and the database state is left unchanged. An atomic system must guarantee atomicity in each and every situation, including power failures, errors, and crashes. To the outside world, a committed transaction appears (by its effects on the database) to be indivisible ("atomic"), and an aborted transaction does not happen." - Wikipedia

"The consistency property ensures that any transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including but not limited to constraints, cascades, triggers, and any combination thereof. This does not guarantee correctness of the transaction in all ways the application programmer might have wanted (that is the responsibility of application-level code) but merely that any programming errors do not violate any defined rules." - Wikipedia

ArcadeDB uses the MVCC to assure consistency by versioning the page where the record are stored.

Look at this example:

"The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially, i.e. one after the other. Providing isolation is the main goal of concurrency control. Depending on concurrency control method, the effects of an incomplete transaction might not even be visible to another transaction." - Wikipedia

Using remote access all the commands are executed on the server, so out of transaction scope. Look below for more information.

Look at these examples:

At operation 7 the client 1 continues to read the same version of x read in operation 2.

At operation 7 the client 1 reads the version of y which was written at operation 6 by client 2. This is because it never reads y before.

"Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors. In a relational database, for instance, once a group of SQL statements execute, the results need to be stored permanently (even if the database crashes immediately thereafter). To defend against power loss, transactions (or their effects) must be recorded in a non-volatile memory." - Wikipedia

An ArcadeDB instance can fail for several reasons:

You can use the ArcadeDB engine directly in the same process of your application. This gives superior performance due to the lack of inter-process communication. In this case, should your application crash (for any reason), the ArcadeDB Engine also crashes.

If you’re using an ArcadeDB Server connected remotely, if your application crashes the engine continue to work, but any pending transaction owned by the client will be rolled back.

At start-up the ArcadeDB Engine checks to if it is restarting from a crash. In this case, the auto-recovery phase starts which rolls back all pending transactions.

ArcadeDB has different levels of durability based on storage type, configuration and settings.

This mode uses the well known Multi Version Control System MVCC by allowing multiple reads and writes on the same records. The integrity check is made on commit. If the record has been saved by another transaction in the interim, then an OConcurrentModificationException will be thrown. The application can choose either to repeat the transaction or abort it.

ArcadeDB does support nested transaction. If further begin() are called after a transaction is already begun, then the new transaction is the current one until commit or rollback. When the nested transaction is completed, the previous transaction becomes the current transaction.

Unlike many Object-relational mapping tools, ArcadeDB does not split documents between different types. Each document resides in one or a number of buckets associated with its specific type. When you execute a query against a type that has subtypes, ArcadeDB searches the buckets of the target type and all subtypes.

In developing your application, bear in mind that ArcadeDB needs to know the type inheritance relationship.

For example,

By default, ArcadeDB treats all queries as polymorphic. Using the example above, you can run the following query from the console:

This query returns all instances of the types Account and Company that have a property name that matches Google.

Consider an example, where you have three types, listed here with the bucket identifier in the parentheses.

By default, ArcadeDB creates a separate bucket for each type. It indicates this bucket by the defaultBucketId property in the type OType and indicates the bucket used by default when not specified. However, the type OType has a property bucketIds, (as int[]), that contains all the buckets able to contain the records of that type. bucketIds and defaultBucketId are the same by default.

When you execute a query against a type, ArcadeDB limits the result-sets to only the records of the buckets contained in the bucketIds property. For example,

This query returns all the records with the name property set to GOOGLE from all three types, given that the base type Account was specified. For the type Account, ArcadeDB searches inside the buckets 10, 13 and 27, following the inheritance specified in the schema.

To start ArcadeDB as a server run the script server.sh under the bin directory of ArcadeDB distribution. If you’re using MS Windows OS, replace server.sh with server.bat.

The first time the server is running, the root password must be inserted and confirmed. The hash (+salt) of the inserted password will be stored in the file config/security.json. To know more about this topic, look at Security. Delete this file and restart the server to reinsert the password for server’s root user.

The default rule of security are pretty basic. The password length must be between 8 and 256 characters. You can implement your own security policy. Check Security Policy.

You can skip the request for the password by passing it as a setting. Example:

-Darcadedb.server.rootPassword=this_is_a_password

Once inserted the password for the root user, you should see this output.

By default, the following components start with the server:

In the output above, the name ArcadeDB_0 is the server name. By default, ArcadeDB_0 is used. To specify a different name define it with the setting server.name, example:

In HA configuration, it’s mandatory all the servers in cluster have different names.

To change the default value of a setting, always put arcadedb. as a prefix. Example:

To change the same setting via Java code:

Check the Appendix for all the available settings.

ArcadeDB supports a High Availability mode where multiple servers share the same database (replication).

In order to start an ArcadeDB server with the support for replication, you need to:

Example:

The log should look like this:

At startup, the ArcadeDB server will look for an existent cluster to join based on the configured list of servers, otherwise a new cluster will be created. In this example we set the server name to FloridaServer.

Every time a server joins a cluster, it starts the process to elect the new Leader. If the cluster exists and already contains a Leader, then the existent Leader is kept. Every time a server leaves the cluster (because it becomes unreachable), the election process is started again. To know more about the RAFT election process, look at RAFT protocol.

Embedding the server in your JVM allows to have all the benefits of working in embedded mode with ArcadeDB (zero cost for network transport and marshalling) and still having the database accessible from the outside, such as Studio, remote API, Postgres, REDIS and MongoDB drivers.

First, add the server library in your classpath. If you’re using Maven include this dependency in your pom.xml file.

This library depends on arcadedb-network-<version>.jar. If you’re using Maven or Gradle it will be imported automatically as a dependency, otherwise please add also the arcadedb-network library to your classpath.

To run ArcadeDB Server with Docker, type this (replace <password> with the root password you want to use):

If there are no errors, Docker prints immediately the container id. You can use that id to stop the container, or execute some commands from it.

To run the console from the container started above, use:

Before starting the cluster, set ArcadeDB Server root password as a secret (replace <password> with the root password you want to use):

This will set the password in the environment variable arcadedb.server.rootPassword. The ArcadeDB server will use this password for the root user.

Now you can start a Kubernetes cluster with 3 servers by using the default configuration:

In order to scale up or down with the number of replicas, use this:

Where the value of <new-number-of-replicas> is the new number of replicas. Example:

Scaling up and down doesn’t affect current workload. There are no pauses when a server enters/exits from the cluster.

More coming soon.

Run the console by executing console.sh under bin directory:

The console supports the following commands (you can always retrieve this help by typing HELP or just ?:

ArcadeDB allows to execute a non-stop backup of a database while it is used without blocking writes or affecting performance. You can execute the backup of a database from SQL.

Look at Backup Database SQL command for more information.

ArcadeDB allows to restore a database previously backed up.

Example

Example for restoring the database "mydb" from the backup located in backups/mysb/mydb-backup-20210921-172750767.zip.

ArcadeDB provides some basic ETL capabilities for automatically importing datasets in any of the following formats:

From file of types:

Located on:

To start importing it’s super easy as providing the URL where the source file to import is located. URLs can be local paths or from the Internet by using http and https.

Example of loading the Freebase RDF dataset:

Example of loading the Discogs dataset in the database on path "/temp/discogs":

Note that in this case the URL is https and the file is compressed with GZip.

Example of importing New York Taxi dataset in CSV format. The first line of the CSV file set the property names:

See also:

SQL Import Database command, Neo4j Importer, OrientDB Importer

ArcadeDB is able to automatically upgrade a database when a newer version of ArcadeDB is used. The migration is completely automatic and transparent.

In the case you need to downgrade to an older version of ArcadeDB, check the binary compatibility between the versions. ArcadeDB uses the semantic versioning with 100% compatibility for migration of databases up or down between patch version (the Z in X.Y.Z). To downgrade to a minor or major, the safest way is to export the database with the newest version and re-import the database with the older version.

ArcadeDB provides HTTP API to interface to the server from a remote application. You can use any programming language that supports HTTP calls (pretty much any language) or use a driver to have a little abstraction over HTTP API.

Add the following dependency in your Maven pom.xml file under the tag <dependencies>: