Command-line Options¶
When an instance of H2O is started from the command-line, users generally call a Java command similar to “java -Xmx1g -jar h2o.jar ” Users can customize their running instance of H2O by changing options from their default value during launch.
There are two different argument types: JVM arguments and H2O arguments that follows the following format when ran: java [JVM OPTIONS] -jar h2o.jar [H2O OPTIONS]
JVM Options¶
For other common as well as advance JVM options not mentioned below search through available VM Options. Typically there are only two options used commonly for H2O’s case.
- -version
- Print java version info and exit. Run a check on the java version to make sure the Java and H2O’s versions are compatible. In particular H2O supports Java 1.6+.
- -Xmx<Heap Size>
- Is a memory allocation option that sets the total heap size for a H2O node. By default this option is set to -Xmx1g. It is recommended to launch nodes with a total of four times the memory than your data. Note: Do not try to launch with more memory than you have available.
H2O Options¶
To access the following list from the command line use option -h or -help.
- -h | -help
- Print this help.
- -version
- Print version info and exit.
- -name <h2oCloudName>
- Cloud name used for discovery of other nodes. Nodes with the same cloud name will form an H2O cloud (also known as an H2O cluster).
- -flatfile <flatFileName>
- Configuration file explicitly listing H2O cloud node members.
- -ip <ipAddressOfNode>
- IP address of this node.
- -port <port>
- Port number for this node (note: port+1 is also used). (The default port is 54321.)
- -network <IPv4network1Specification>[,<IPv4network2Specification> ...]
- The IP address discovery code will bind to the first interface that matches one of the networks in the comma-separated list. Use instead of -ip when a broad range of addresses is legal. (Example network specification: ‘10.1.2.0/24’ allows 256 legal possibilities.)
- -ice_root <fileSystemPath>
- The directory where H2O spills temporary data to disk. (The default is ‘/tmp/h2o-Amy’.)
- -single_precision
- Reduce the max. (storage) precision for floating point numbers from double to single precision to save memory of numerical data. (The default is double precision.)
- -nthreads <# of threads>
- Maximum number of threads in the low priority batch-work queue. (The default is 4*numcpus.)
- -license <licenseFilePath>
- Path to license file on local filesystem.
Cloud formation behavior¶
New H2O nodes join together to form a cloud at startup time. Once a cloud is given work to perform, it locks out new members from joining. H2O works best on distributed multinode clusters when the clusters are similar in configuration, and allocated equal amounts of memory.
Examples:
- Start an H2O node with 4GB of memory and a default cloud name:
- $ java -Xmx4g -jar h2o.jar
- Start an H2O node with 6GB of memory and a specified cloud name:
- $ java -Xmx6g -jar h2o.jar -name TomsCloud
- Start an H2O cloud with three 2GB nodes and a specified cloud name:
- $ java -Xmx2g -jar h2o.jar -name TomsCloud $ java -Xmx2g -jar h2o.jar -name TomsCloud $ java -Xmx2g -jar h2o.jar -name TomsCloud