General Options

Database Upgrade

--database.auto-upgrade

Specifying this option will make the server perform a database upgrade at start. A database upgrade will first compare the version number stored in the file VERSION in the database directory with the current server version.

If the two version numbers match, the server will start normally.

If the version number found in the database directory is higher than the version number the server is running, the server expects this is an unintentional downgrade and will warn about this. It will however start normally. Using the server in these conditions is however not recommended nor supported.

If the version number found in the database directory is lower than the version number the server is running, the server will check whether there are any upgrade tasks to perform. It will then execute all required upgrade tasks and print their statuses. If one of the upgrade tasks fails, the server will exit and refuse to start. Re-starting the server with the upgrade option will then again trigger the upgrade check and execution until the problem is fixed. If all tasks are finished, the server will start normally.

Whether or not this option is specified, the server will always perform a version check on startup. Running the server with a non-matching version number in the VERSION file will make the server refuse to start.

Storage Engine

As of ArangoDB 3.2 two storage engines are supported. The "traditional" engine is called MMFiles, which is also the default storage engine.

An alternative engine based on RocksDB is also provided and can be turned on manually.

One storage engine type is supported per server per installation. Live switching of storage engines on already installed systems isn't supported. Configuring the wrong engine (not matching the previously used one) will result in the server refusing to start. You may however use auto to let ArangoDB choose the previously used one.

--server.storage-engine [auto|mmfiles|rocksdb]

Daemon

--daemon

Runs the server as a daemon (as a background process). This parameter can only be set if the pid (process id) file is specified. That is, unless a value to the parameter pid-file is given, then the server will report an error and exit.

Default Language

--default-language default-language

The default language ist used for sorting and comparing strings. The language value is a two-letter language code (ISO-639) or it is composed by a two-letter language code with and a two letter country code (ISO-3166). Valid languages are "de", "en", "en_US" or "en_UK".

The default default-language is set to be the system locale on that platform.

Supervisor

--supervisor

Executes the server in supervisor mode. In the event that the server unexpectedly terminates due to an internal error, the supervisor will automatically restart the server. Setting this flag automatically implies that the server will run as a daemon. Note that, as with the daemon flag, this flag requires that the pid-file parameter will set.

unix> ./arangod --supervisor --pid-file /var/run/arangodb.pid /tmp/vocbase/
2012-06-27T15:58:28Z [10133] INFO starting up in supervisor mode

As can be seen (e.g. by executing the ps command), this will start a supervisor process and the actual database process:

unix> ps fax | grep arangod
10137 ?        Ssl    0:00 ./arangod --supervisor --pid-file /var/run/arangodb.pid /tmp/vocbase/
10142 ?        Sl     0:00  \_ ./arangod --supervisor --pid-file /var/run/arangodb.pid /tmp/vocbase/

When the database process terminates unexpectedly, the supervisor process will start up a new database process:

> kill -SIGSEGV 10142

> ps fax | grep arangod
10137 ?        Ssl    0:00 ./arangod --supervisor --pid-file /var/run/arangodb.pid /tmp/vocbase/
10168 ?        Sl     0:00  \_ ./arangod --supervisor --pid-file /var/run/arangodb.pid /tmp/vocbase/

User identity

--uid uid

The name (identity) of the user the server will run as. If this parameter is not specified, the server will not attempt to change its UID, so that the UID used by the server will be the same as the UID of the user who started the server. If this parameter is specified, then the server will change its UID after opening ports and reading configuration files, but before accepting connections or opening other files (such as recovery files). This is useful when the server must be started with raised privileges (in certain environments) but security considerations require that these privileges be dropped once the server has started work.

Observe that this parameter cannot be used to bypass operating system security. In general, this parameter (and its corresponding relative gid) can lower privileges but not raise them.

Group identity

--gid gid

The name (identity) of the group the server will run as. If this parameter is not specified, then the server will not attempt to change its GID, so that the GID the server runs as will be the primary group of the user who started the server. If this parameter is specified, then the server will change its GID after opening ports and reading configuration files, but before accepting connections or opening other files (such as recovery files).

This parameter is related to the parameter uid.

Process identity

--pid-file filename

The name of the process ID file to use when running the server as a daemon. This parameter must be specified if either the flag daemon or supervisor is set.

Console

--console

Runs the server in an exclusive emergency console mode. When starting the server with this option, the server is started with an interactive JavaScript emergency console, with all networking and HTTP interfaces of the server disabled.

No requests can be made to the server in this mode, and the only way to work with the server in this mode is by using the emergency console. Note that the server cannot be started in this mode if it is already running in this or another mode.

Random Generator

--random.generator arg

The argument is an integer (1,2,3 or 4) which sets the manner in which random numbers are generated. The default method (3) is to use the a non-blocking random (or pseudorandom) number generator supplied by the operating system.

Specifying an argument of 2, uses a blocking random (or pseudorandom) number generator. Specifying an argument 1 sets a pseudorandom number generator using an implication of the Mersenne Twister MT19937 algorithm. Algorithm 4 is a combination of the blocking random number generator and the Mersenne Twister.

Enable/disable authentication

--server.authentication Setting this option to false will turn off authentication on the server side so all clients can execute any action without authorization and privilege checks. The default value is true.

JWT Secret

--server.jwt-secret secret

ArangoDB will use JWTs to authenticate requests. Using this option lets you specify a JWT.

In single server setups and when not specifying this secret ArangoDB will generate a secret.

In cluster deployments which have authentication enabled a secret must be set consistently across all cluster tasks so they can talk to each other.

Enable/disable authentication for UNIX domain sockets

--server.authentication-unix-sockets value

Setting value to true will turn off authentication on the server side for requests coming in via UNIX domain sockets. With this flag enabled, clients located on the same host as the ArangoDB server can use UNIX domain sockets to connect to the server without authentication. Requests coming in by other means (e.g. TCP/IP) are not affected by this option.

The default value is false.

Note: this option is only available on platforms that support UNIX domain sockets.

Enable/disable authentication for system API requests only

--server.authentication-system-only boolean Controls whether incoming requests need authentication only if they are directed to the ArangoDB's internal APIs and features, located at /_api/, /_admin/ etc. If the flag is set to true, then HTTP authentication is only required for requests going to URLs starting with /_, but not for other URLs. The flag can thus be used to expose a user-made API without HTTP authentication to the outside world, but to prevent the outside world from using the ArangoDB API and the admin interface without authentication. Note that checking the URL is performed after any database name prefix has been removed. That means when the actual URL called is /_db/_system/myapp/myaction, the URL /myapp/myaction will be used for authentication-system-only check. The default is true. Note that authentication still needs to be enabled for the server regularly in order for HTTP authentication to be forced for the ArangoDB API and the web interface. Setting only this flag is not enough. You can control ArangoDB's general authentication feature with the --server.authentication flag.

Enable/disable replication applier

--database.replication-applier flag

If false the server will start with replication appliers turned off, even if the replication appliers are configured with the autoStart option. Using the command-line option will not change the value of the autoStart option in the applier configuration, but will suppress auto-starting the replication applier just once.

If the option is not used, ArangoDB will read the applier configuration from the file REPLICATION-APPLIER-CONFIG on startup, and use the value of the autoStart attribute from this file.

The default is true.

Keep-alive timeout

--http.keep-alive-timeout

Allows to specify the timeout for HTTP keep-alive connections. The timeout value must be specified in seconds. Idle keep-alive connections will be closed by the server automatically when the timeout is reached. A keep-alive-timeout value 0 will disable the keep alive feature entirely.

Hide Product header

--http.hide-product-header

If true, the server will exclude the HTTP header "Server: ArangoDB" in HTTP responses. If set to false, the server will send the header in responses.

The default is false.

Allow method override

--http.allow-method-override

When this option is set to true, the HTTP request method will optionally be fetched from one of the following HTTP request headers if present in the request:

x-http-method
x-http-method-override
x-method-override

If the option is set to true and any of these headers is set, the request method will be overridden by the value of the header. For example, this allows issuing an HTTP DELETE request which to the outside world will look like an HTTP GET request. This allows bypassing proxies and tools that will only let certain request types pass.

Setting this option to true may impose a security risk so it should only be used in controlled environments.

The default value for this option is false.

Server threads

--server.threads number

Specifies the number of threads that are spawned to handle requests.

Toggling server statistics

--server.statistics value

If this option is value is false, then ArangoDB's statistics gathering is turned off. Statistics gathering causes regular CPU activity so using this option to turn it off might relieve heavy-loaded instances a bit.

Session timeout

time to live for server sessions --server.session-timeout value

The timeout for web interface sessions, using for authenticating requests to the web interface (/_admin/aardvark) and related areas.

Sessions are only used when authentication is turned on.

Foxx queues

enable or disable the Foxx queues feature --foxx.queues flag If true, the Foxx queues will be available and jobs in the queues will be executed asynchronously. The default is true. When set to false the queue manager will be disabled and any jobs are prevented from being processed, which may reduce CPU load a bit.

Foxx queues poll interval

poll interval for Foxx queues --foxx.queues-poll-interval value The poll interval for the Foxx queues manager. The value is specified in seconds. Lower values will mean more immediate and more frequent Foxx queue job execution, but will make the queue thread wake up and query the queues more often. When set to a low value, the queue thread might cause CPU load. The default is 1 second. If Foxx queues are not used much, then this value may be increased to make the queues thread wake up less.

Journal size

--database.maximal-journal-size size Maximal size of journal in bytes. Can be overwritten when creating a new collection. Note that this also limits the maximal size of a single document. The default is 32MB.

Wait for sync

default wait for sync behavior --database.wait-for-sync boolean Default wait-for-sync value. Can be overwritten when creating a new collection. The default is false.

Force syncing of properties

force syncing of collection properties to disk --database.force-sync-properties boolean Force syncing of collection properties to disk after creating a collection or updating its properties. If turned off, no fsync will happen for the collection and database properties stored in parameter.json files in the file system. Turning off this option will speed up workloads that create and drop a lot of collections (e.g. test suites). The default is true.

Limiting memory for AQL queries

--query.memory-limit value

The default maximum amount of memory (in bytes) that a single AQL query can use. When a single AQL query reaches the specified limit value, the query will be aborted with a resource limit exceeded exception. In a cluster, the memory accounting is done per shard, so the limit value is effectively a memory limit per query per shard.

The global limit value can be overriden per query by setting the memoryLimit option value for individual queries when running an AQL query.

The default value is 0, meaning that there is no memory limit.

Turning AQL warnings into errors

--query.fail-on-warning value

When set to true, AQL queries that produce warnings will instantly abort and throw an exception. This option can be set to catch obvious issues with AQL queries early. When set to false, AQL queries that produce warnings will not abort and return the warnings along with the query results. The option can also be overridden for each individual AQL query.

Enable/disable AQL query tracking

--query.tracking flag

If true, the server's AQL slow query tracking feature will be enabled by default. Tracking of queries can be disabled by setting the option to false.

The default is true.

Threshold for slow AQL queries

--query.slow-threshold value

By setting value it can be controlled after what execution time an AQL query is considered "slow". Any slow queries that exceed the execution time specified in value will be logged when they are finished. The threshold value is specified in seconds. Tracking of slow queries can be turned off entirely by setting the option --query.tracking to false.

The default value is 10.0.

Throw collection not loaded error

--database.throw-collection-not-loaded-error flag

Accessing a not-yet loaded collection will automatically load a collection on first access. This flag controls what happens in case an operation would need to wait for another thread to finalize loading a collection. If set to true, then the first operation that accesses an unloaded collection will load it. Further threads that try to access the same collection while it is still loading will get an error (1238, collection not loaded). When the initial operation has completed loading the collection, all operations on the collection can be carried out normally, and error 1238 will not be thrown.

If set to false, the first thread that accesses a not-yet loaded collection will still load it. Other threads that try to access the collection while loading will not fail with error 1238 but instead block until the collection is fully loaded. This configuration might lead to all server threads being blocked because they are all waiting for the same collection to complete loading. Setting the option to true will prevent this from happening, but requires clients to catch error 1238 and react on it (maybe by scheduling a retry for later).

The default value is false.

AQL Query caching mode

--query.cache-mode

Toggles the AQL query cache behavior. Possible values are:

off: do not use query cache
on: always use query cache, except for queries that have their cache attribute set to false
demand: use query cache only for queries that have their cache attribute set to true

AQL Query cache size

--query.cache-entries

Maximum number of query results that can be stored per database-specific query cache. If a query is eligible for caching and the number of items in the database's query cache is equal to this threshold value, another cached query result will be removed from the cache.

This option only has an effect if the query cache mode is set to either on or demand.

V8 contexts

--javascript.v8-contexts number

Specifies the maximum number of V8 contexts that are created for executing JavaScript code. More contexts allow executing more JavaScript actions in parallel, provided that there are also enough threads available. Please note that each V8 context will use a substantial amount of memory and requires periodic CPU processing time for garbage collection.

Note that this value configures the maximum number of V8 contexts that can be used in parallel. Upon server start only as many V8 contexts will be created as are configured in option --javascript.v8-contexts-minimum. The actual number of available V8 contexts may float at runtime between --javascript.v8-contexts-minimum and --javascript.v8-contexts. When there are unused V8 contexts that linger around, the server's garbage collector thread will automatically delete them.

--javascript.v8-contexts-minimum number

Specifies the minimum number of V8 contexts that will be present at any time the server is running. The actual number of V8 contexts will never drop below this value, but it may go up as high as specified via the option --javascript.v8-contexts.

When there are unused V8 contexts that linger around and the number of V8 contexts is greater than --javascript.v8-contexts-minimum the server's garbage collector thread will automatically delete them.

Garbage collection frequency (time-based)

--javascript.gc-frequency frequency

Specifies the frequency (in seconds) for the automatic garbage collection of JavaScript objects. This setting is useful to have the garbage collection still work in periods with no or little numbers of requests.

Garbage collection interval (request-based)

--javascript.gc-interval interval

Specifies the interval (approximately in number of requests) that the garbage collection for JavaScript objects will be run in each thread.

V8 options

--javascript.v8-options options

Optional arguments to pass to the V8 Javascript engine. The V8 engine will run with default settings unless explicit options are specified using this option. The options passed will be forwarded to the V8 engine which will parse them on its own. Passing invalid options may result in an error being printed on stderr and the option being ignored.

Options need to be passed in one string, with V8 option names being prefixed with double dashes. Multiple options need to be separated by whitespace. To get a list of all available V8 options, you can use the value "--help" as follows:

--javascript.v8-options="--help"

Another example of specific V8 options being set at startup:

--javascript.v8-options="--log"

Names and features or usable options depend on the version of V8 being used, and might change in the future if a different version of V8 is being used in ArangoDB. Not all options offered by V8 might be sensible to use in the context of ArangoDB. Use the specific options only if you are sure that they are not harmful for the regular database operation.