Transparent Job Distribution With qtcsh

qtcsh is a fully compatible replacement for the widely known and used UNIX C shell derivative tcsh. qtcsh is built around tcsh. See the information that is provided in sge-root/3rd_party for details on the involvement of tcsh. qtcsh provides a command shell with the extension of transparently distributing execution of designated applications to suitable and lightly loaded hosts that use the grid engine system. The .qtask configuration files define the applications to execute remotely and the requirements that apply to the selection of an execution host.

These applications are transparent to the user and are submitted to the grid engine system through the qrsh facility. qrsh provides standard output, error output, and standard input handling as well as terminal control connection to the remotely executing application. Three noticeable differences between running such an application remotely and running the application on the same host as the shell are:

• The remote host might be more powerful, lower-loaded, and have required hardware and software resources installed. Therefore, such a remote host would be much better suited than the local host, which might not allow running the application at all.

• A small delay is incurred by the remote startup of the jobs and by their handling through the grid engine system.

• Administrators can restrict the use of resources through interactive jobs (qrsh) and thus through qtcsh. If not enough suitable resources are available for an application to be started through qrsh, or if all suitable systems are overloaded, the implicit qrsh submission fails. A corresponding error message is returned, such as Not enough resources ... try later.

In addition to the standard use, qtcsh is a suitable platform for third-party code and tool integration. The single-application execution form of qtcsh is qtcsh -c app-name. The use of this form of qtcsh inside integration environments presents a persistent interface that almost never needs to be changed. All the required application, tool, integration, site, and even user-specific configurations are contained in appropriately defined .qtask files. A further advantage is that this interface can be used in shell scripts of any type, in C programs, and even in Java applications.

qtcsh Usage

The invocation of qtcsh is exactly the same as for tcsh. qtcsh extends tcsh in providing support for the .qtask file and by offering a set of specialized shell built-in modes.

The .qtask file is defined as follows. Each line in the file has the following format:

% [!]app-name qrsh-options

The optional leading exclamation mark (!) defines the precedence between conflicting definitions in a global cluster .qtask file and the personal .qtask file of the qtcsh user. If the exclamation mark is missing in the global cluster file, a conflicting definition in the user file overrides the definition in the global cluster file. If the exclamation mark is in the global cluster file, the corresponding definition cannot be overridden.

app-name specifies the name of the application that, when typed on a command line in a qtcsh, is submitted to the grid engine system for remote execution.

qrsh-options specifies the options to the qrsh facility to use. These options define resource requirements for the application.

The application name must appear in the command line exactly as the application is defined in the .qtask file. If the application name is prefixed with a path name, a local binary is addressed. No remote execution is intended.

csh aliases are expanded before a comparison with the application names is performed. The applications intended for remote execution can also appear anywhere in a qtcsh command line, in particular before or after standard I/O redirections.

Hence, the following examples are valid and meaningful syntax:

# .qtask file
netscape -v DISPLAY=myhost:0
grep -l h=filesurfer

Given this .qtask file, the following qtcsh command lines:

netscape
~/mybin/netscape
cat very_big_file | grep pattern | sort | uniq

implicitly result in:

qrsh -v DISPLAY=myhost:0 netscape
~/mybin/netscape
cat very_big_file | qrsh -l h=filesurfer grep pattern | sort | uniq

qtcsh can operate in different modes, influenced by switches that can be set on or off:

• Local or remote execution of commands. Remote is the default.

• Immediate or batch remote execution. Immediate is the default.

• Verbose or nonverbose output. Nonverbose is the default.

The setting of these modes can be changed using option arguments of qtcsh at start time or with the shell built-in command qrshmode at runtime. See the qtcsh(1) man page for more information.