boinc/doc/file_access.html

<title>Compute Model: Remote File Access</title> 
<h2>Compute Model: Remote File Access</h2> 
<p>
Output files can be designated as sticky but not
upload-when-present.
Sometimes this is done because the file will be
used as an input for a later workunit; it may also be done to spread
large output data across participant disks, in cases where the data may
be too large to store on the project back-end. 
<p>
To access such a file, the back end inserts a <b>file access
request</b> in the database.
This specifies a file and a data-server URL.
When a host storing the file contacts the scheduling server (which
may not happen for a while) the scheduling server forwards the file
access request.
The host confirms the file transfer when it is
completed; the back-end must poll for this event.