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Tablet Server At Any Point Of Time

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Tablet Assignment A tablet is assigned to one tablet server at any point of time. The master is responsible to keep track of the set of live tablet servers, and the current assignment of tablets to tablet servers, including which tablets are unassigned. If a tablet is unassigned, and place is available in a tablet server; the master assigns the tablet by sending a tablet load request to the tablet server. Chubby keep track of tablet servers. When a tablet server starts, it creates, and acquires an exclusive lock on, a uniquely named file in a specific Chubby directory. The master monitors this directory (the server’s directory) to discover tablet servers. Whenever a master is started by the Bigtable cluster management system, it executes the following steps to discover the current tablet assignments (1) The master grabs a unique master lock in Chubby, which prevents con-current master instantiations. (2) The master scans the server’s directory in Chubby to find the live servers. (3) The master communicates with every live tablet server to discover what tablets are already assigned to each server. (4) The master scans the METADATA table to learn the set of tablets. (5) Builds a set of unassigned tablet, which are become eligible for assignment. Tablet splits are treated specially since a tablet server initiates them. The tablet server commits the split by recording information for the new tablet in the METADATA table. When the split has committed, it notifies the master.

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