Database Reference
In-Depth Information
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call adios{\_}finalize ()
Adios init () initiates parsing of the configuration file generating all of the
internal data type information, configures the mechanisms described above,
and potentially sets up the buffer. Buffer creation can be delayed until a
subsequent call to adios allocate buffer if it should be based on a percentage
of free memory or other allocation-time-sensitive considerations.
Adios begin calculuation () and adios end calculation () provide the
“ticker” mechanism for asynchronous I/O, providing the asynchronous I/O
mechanism with information about the compute phases, so that the I/O can
be performed at times when the application is not engaged in communica-
tions. The subsequent “end” call indicates that the code wishes to perform
communication, ratcheting back any I/O use of bandwidth.
Adios end iteration () is a pacing function designed to give feedback to
asynchronous I/O to gauge what progress must be made with data transmis-
sion in order to keep up with the code. For example, if a checkpoint/restart * is
written every 100 iterations, the XML file may indicate an iteration count that
is less than 100, to evacuate the data in order to accommodate possible storage
congestion or other issues, such as a high demand on the shared network.
Adios finalize () indicates the code is about to shut down and any asyn-
chronous operations need to complete. It will block until all of the data has
been drained from the compute node.
We describe next two asynchronous I/O mechanisms underlying ADIOS.
Note that these mechanisms target current day supercomputers, which are
typically composed of login nodes, I/O nodes, and compute nodes.
5.2.2 DataTaps and DataTap Servers
DataTap addresses the following performance issues for high-throughput data
movement:
Scaling to large data volumes and large numbers of I/O clients given
limited I/O resources
Avoiding excessive CPU and memory overheads on the compute nodes
Balancing bandwidth utilization across the system
Offering additional I/O functionality to the end users, including on-
demand data annotation and filtering
* When running simulations with many time steps, it is customary to write out checkpoint/restart
data following a number of time steps, in case the computation needs to backtrack, thus avoiding
repeating the computation from the start.
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