[[PageOutline]]

= Distributed data management =

BOINC provides features for implementing distributed data management systems.

Such a system is implemented as several components:

 * A "plug-in" to the BOINC scheduler, which is called on each scheduler RPC;
 * A daemon program that handles timeouts;
 * Interface programs, for example, programs allowing users to submit and retrieve files.

Note: to use these features, you must include
{{{
<msg_to_host/>
}}}
in your config.xml.

== Sending files to hosts ==

From an interface program or daemon, call

{{{
int send_file(int host_id, const char* file_name)
}}}

or use the command line program

{{{
send_file --host_id X --file_name Y
}}}

From the scheduler plugin, call

{{{
int send_file_sched(const char* filename);
}}}

== Retrieving files ==

From an interface program or daemon, call

{{{
int get_file(int host_id, const char* file_name)
}}}

or use the command line program

{{{
get_file --host_id X --file_name Y
}}}


From the scheduler plugin, call

{{{
int get_file_sched(const char* filename);
}}}

== Deleting files ==

From an interface program or daemon, call

{{{
int delete_file(int host_id, const char* file_name)
}}}

or use the command line program

{{{
delete_file -host_id X -file_name Y
}}}

From the scheduler plugin, call

{{{
int delete_file_sched(const char* filename);
}}}

== Implementation ==

From interface programs,
'''put_file''' and '''get_file''' create a message to the host (in the msg_to_host table).
The message is a chunk of XML that describes a "virtual" app and app version
(with no associate executable),
and a workunit and result that contain a single input or output file.
The result has a name of the form '''file_xfer_*''',
which tells the scheduler to treat it specially.