Use in Distributed Shared Memory Systems
In distributed shared memory, checkpointing is a technique that helps tolerate the errors leading to losing the effect of work of long-running applications. The main property which should be induced by checkpointing techniques in such systems is in preserving system consistency in case of failure. There are two main approaches to checkpointing in such systems: coordinated checkpointing, in which all cooperating processes work together to establish coherent checkpoint; and communication induced (called also dependency induced) independent checkpointing.
It must be stressed that simply forcing processes to checkpoint their state at fixed time intervals is not sufficient to ensure global consistency. Even if we postulate the existence of global clock, the checkpoints made by different processes still may not form a consistent state. The need for establishing a consistent state may force other process to roll back to their checkpoints, which in turn may cause other processes to roll back to even earlier checkpoints, which in the most extreme case may mean that the only consistent state found is the initial state (the so called domino effect).
In the coordinated checkpointing approach, processes must ensure that their checkpoints are consistent. This is usually achieved by some kind of two-phase commit protocol algorithm. In communication induced checkpointing, each process checkpoints its own state independently whenever this state is exposed to other processes (that is, for example whenever a remote process reads the page written to by the local process).
The system state may be saved either locally, in stable storage, or in a distant node's memory.
Read more about this topic: Application Checkpointing
Famous quotes containing the words distributed, shared, memory and/or systems:
“Indiana was really, I suppose, a Democratic State. It has always been put down in the book as a state that might be carried by a close and careful and perfect organization and a great deal of—[from audience: “soap”Ma reference to purchased votes, the word being followed by laughter].
I see reporters here, and therefore I will simply say that everybody showed a great deal of interest in the occasion, and distributed tracts and political documents all through the country.”
—Chester A. Arthur (1829–1886)
“The danger lies in forgetting what we had. The flow between generations becomes a trickle, grandchildren tape-recording grandparents’ memories on special occasions perhaps—no casual storytelling jogged by daily life, there being no shared daily life what with migrations, exiles, diasporas, rendings, the search for work. Or there is a shared daily life riddled with holes of silence.”
—Adrienne Rich (b. 1929)
“We turned to other things.
I haven’t any memory have you?
Of ever coming to the place again
To see if the birds lived the first night through.
And so at last to learn to use their wings.”
—Robert Frost (1874–1963)
“No civilization ... would ever have been possible without a framework of stability, to provide the wherein for the flux of change. Foremost among the stabilizing factors, more enduring than customs, manners and traditions, are the legal systems that regulate our life in the world and our daily affairs with each other.”
—Hannah Arendt (1906–1975)