One use case for optimistic locking is to have your application use the database to allow one of your threads / hosts to 'claim' a task. This is a technique that has come in handy for me on a regular basis.
Island arcs are volcanic islands that form parallel to ocean trenches in subduction zones. The Pacific Ring of Fire is home to many of these groups of islands. Volcanoes that form above hot spots like the Hawaiian islands are not volcanic arcs.Volcanic island eruption, USGS. Two oceanic plates converge. Islands form an arc when two oceanic plates converge creating a row of islands above the overriding plate.The older plate, which is heavier and denser, is forced beneath the lighter plate.he melting plate feeds magma chambers that supply volcanic islands that form an arc when the molten rock erupts onto the ocean floor of the overriding plate. Mariana Islands. Deep ocean trenches form between the converging plates.
Alaska's Aleutian islands, all volcanic in origin and formed from the subduction of the Pacific plate beneath the North American, represent the northern arc of the Ring of Fire. The ring then sweeps down along Russia's Kamchatka Peninsula and through Japan, where the Pacific plate dives beneath the Eurasian plate.