Configuration is managed differently for Accumulo clients and servers.
[Accumulo clients][accumulo-client] are created using Java builder methods, a Java properties object or an [accumulo-client.properties] file containing [client properties].
Accumulo processes (i.e master, tablet server, monitor, etc) are configured by [server properties] whose values can be set in the following configuration locations (with increasing precedence) that are described in detail below:
If a property is set in multiple locations, the value in the location with the highest precedence is used.
These configuration locations are described in detail below:
All [server properties] have a default value. Default values are set in the source code and can be viewed for each property on the [server properties] page. While default values have the lowest precedence, they are usually optimal. However, there are cases where a change can increase query and ingest performance.
Site configuration refers to [server properties] set in the [accumulo.properties] file which can be found in the conf/ directory. Site configuration will override the default value of a property. If you are running Accumulo on a cluster, any updates to accumulo.properties must be synced across the cluster. Accumulo processes (master, tserver, etc) read their local [accumulo.properties] on start up so processes must be restarted to apply changes. Certain properties can only be set in accumulo.properties. These properties have zk mutable: no in their description. Setting properties in accumulo.properties allows you to configure tablet servers with different settings.
Site configuration can be overriden when starting an Accumulo process on the command line (by using the -o option):
accumulo tserver -o instance.secret=mysecret -o instance.zookeeper.host=localhost:2181
Overriding properties is useful if you can‘t change [accumulo.properties]. It’s done when running Accumulo using Docker.
System configuration refers to [server properties] set for the entire Accumulo instance/cluster. These settings are stored in ZooKeeper and can identified by zk mutable: yes in their description on the [server properties] page. System configuration will override any site configuration set in [accumulo.properties]. While most system configuration settings take effect immediately, some require a restart of the process which is indicated in the zk mutable section of their description. System configuration can be set using the following shell command:
config -s PROPERTY=VALUE
They can also be set using {% jlink org.apache.accumulo.core.client.admin.InstanceOperations %} in the Java API:
client.instanceOperations().setProperty("table.durability", "flush");
Namespace configuration refers to [table.* properties] set for a certain table namespace (i.e group of tables). These settings are stored in ZooKeeper. Namespace configuration will override System configuration and can be set using the following shell command:
config -ns NAMESPACE -s PROPERTY=VALUE
It can also be set using {% jlink org.apache.accumulo.core.client.admin.NamespaceOperations %} in the Java API:
client.namespaceOperations().setProperty("mynamespace", "table.durability", "sync");
Table configuration refers to [table.* properties] set for a certain table. These settings are stored in ZooKeeper and can be set using the following shell command:
config -t TABLE -s PROPERTY=VALUE
They can also be set using {% jlink org.apache.accumulo.core.client.admin.TableOperations %} in the Java API:
client.tableOperations().setProperty("mytable", "table.durability", "log");
Any [server properties] that are set in Zookeeper should consider the limitations of Zookeeper itself with respect to the number of nodes and the size of the node data. Custom table properties and options for Iterators configured on tables are two areas in which there aren't any fail safes built into the API that can prevent the user from making this mistake.
While these properties have the ability to add some much needed dynamic configuration tools, use cases which might fall into these warnings should be reconsidered.
Accumulo's current configuration can be viewed in the shell using the config command.
config - view configuration for the entire systemconfig -ns <NAMESPACE> - view configuration for a specific namespaceconfig -t <TABLE> - view configuration for a specific tableBelow is example shell output from viewing configuration for the table foo. Please note how table.compaction.major.ratio is set in multiple locations but the value 1.6 set in the table scope is used as it has the highest precedence.
root@accumulo-instance> config -t foo ---------+---------------------------------------------+----------------------- SCOPE | NAME | VALUE ---------+---------------------------------------------+----------------------- default | table.bloom.enabled ....................... | false default | table.bloom.error.rate .................... | 0.5% default | table.bloom.hash.type ..................... | murmur default | table.bloom.load.threshold ................ | 1 default | table.bloom.size .......................... | 1048576 default | table.cache.block.enable .................. | false default | table.cache.index.enable .................. | false default | table.compaction.major.everything.at ...... | 19700101000000GMT default | table.compaction.major.everything.idle .... | 1h default | table.compaction.major.ratio .............. | 1.3 site | @override .............................. | 1.4 system | @override .............................. | 1.5 table | @override .............................. | 1.6 default | table.compaction.minor.idle ............... | 5m default | table.compaction.minor.logs.threshold ..... | 3 default | table.failures.ignore ..................... | false
[accumulo-client]: {% durl getting-started/clients#creating-an-accumulo-client %} [client properties]: {% durl configuration/client-properties %} [server properties]: {% durl configuration/server-properties %} [table.* properties]: {% purl table.* %} [accumulo-client.properties]: {% durl configuration/files#accumulo-clientproperties %} [accumulo.properties]: {% durl configuration/files#accumuloproperties %} [Zookeeper Administration Documentation]: https://zookeeper.apache.org/doc/r3.5.7/zookeeperAdmin.html