mirror of https://github.com/BOINC/boinc.git
67 lines
2.1 KiB
PHP
67 lines
2.1 KiB
PHP
<?
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require_once("docutil.php");
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page_head("Persistent file transfer");
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echo "
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<p>
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A file upload or download may experience various types of
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<b>transient failures</b>:
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<ul>
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<li> One or more data servers have failed.
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<li> A network connection fails.
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<li> The host PC is turned off or the core client quits.
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</ul>
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BOINC uses a mechanism called <b>persistent file transfer</b>
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for efficiently recovering from these conditions,
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and deciding when a <b>permanent failure</b> has occurred.
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<p>
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The FILE_XFER class encapsulates a single transfer session
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to a particular data server.
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If the file has previously partially transferred,
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FILE_XFER resumes at the appropriate point.
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<p>
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The PERS_FILE_XFER class encapsulates a persistent file transfer,
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which may involve a sequence of FILE_XFERs,
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possibly to different data servers.
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<p>
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When a file is involved in a persistent file transfer,
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the state is saved in the client state file
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in the following XML element
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(included in the <file_info> element):
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<pre>
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<persistent_file_xfer>
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<num_retries>2</num_retries>
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<first_request_time>1030665600</first_request_time>
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<next_request_time>1030665725</next_request_time>
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</persistent_file_xfer>
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</pre>
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<ul>
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<li> The <b>num_retries</b> element is the number of
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transfer sessions so far.
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<li> The <b>first_request_time</b> element is the time
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the first transfer session started.
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<li> The <b>next_request_time</b> element is the earliest time
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to start a new transfer session.
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</ul>
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<p>
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When there is a transient failure, the core client
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increments num_retries and calculates a new next_request_time
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based on randomized exponential backoff, given by
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<pre>
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next_request_time = current_time+max(MIN_DELAY,min(MAX_DELAY,exp(rand(0,1)*num_retries)))
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</pre>
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Where MIN_DELAY is 1 minute and MAX_DELAY is 4 hours.
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<p>
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The client classifies the transfer as a permanent failure if the
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current time becomes much later than this (default is two weeks).
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??? later than what?
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In this event, the file will be deleted and the failure reported
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to the scheduling server.
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??? in what form?
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";
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page_tail();
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?>
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