Accumulo processes (i.e. manager, tablet server, monitor, etc.) are configured by server properties whose values can be set in the following configuration locations (with increasing precedence):

Default - All properties have a default value
Site - Properties set in accumulo.properties
System - Properties set using shell or Java API that apply to entire Accumulo instance
Namespace - Table properties set using shell or Java API that apply to a table namespace
Table - Table properties set using shell or Java API that apply to a table.

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:

Default

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

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 (manager, 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

System configuration refers to server properties set for the entire Accumulo instance/cluster. These settings are stored in ZooKeeper and can be 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 InstanceOperations in the Java API:

client.instanceOperations().setProperty("table.durability", "flush");

The java api also supports adding, modifying and removing multiple properties in a single operation:

client.instanceOperations().modifyProperties(properties -> {
  properties.remove("table.file.max");
  properties.put("table.bloom.enabled", "true");
  properties.put("table.bloom.error.rate", "0.75");
  properties.put("table.bloom.size", "128000");
});

Namespace

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 NamespaceOperations in the Java API:

client.namespaceOperations().setProperty("mynamespace", "table.durability", "sync");

The java api also supports adding, modifying and removing multiple properties in a single operation:

client.namespaceOperations().modifyProperties("mynamespace", properties -> {
        properties.remove("table.file.max");
        properties.put("table.bloom.enabled", "true");
        properties.put("table.bloom.error.rate", "0.75");
        properties.put("table.bloom.size", "128000");
        });

### Table

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 [TableOperations](https://static.javadoc.io/org.apache.accumulo/accumulo-core/2.1.2/org/apache/accumulo/core/client/admin/TableOperations.html) in the Java API:

```java
client.tableOperations().setProperty("mytable", "table.durability", "log");

The java api also supports adding, modifying and removing multiple properties in a single operation:

client.tableOperations().modifyProperties("mytable", properties -> {
        properties.remove("table.file.max");
        properties.put("table.bloom.enabled", "true");
        properties.put("table.bloom.error.rate", "0.75");
        properties.put("table.bloom.size", "128000");
        });

Zookeeper Considerations

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.

Viewing Server Configuration

Accumulo’s current configuration can be viewed in the shell using the config command.

config - view configuration for the entire system
config -ns <NAMESPACE> - view configuration for a specific namespace
config -t <TABLE> - view configuration for a specific table

Below is an 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 because 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

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