Efficient snapshot read of a database in a distributed storage system
Abstract:
A computer system issues a batch read operation to a tablet in a first replication group in a distributed database and obtains a most recent version of data items in the tablet that have a timestamp no great than a snapshot timestamp T. For each data item in the one tablet, the computer system determines whether the data item has a move-in timestamp less than or equal to the snapshot timestamp T, which is less than a move-out timestamp, and whether the data item has a creation timestamp less than the snapshot timestamp T, which is less than or equal to a deletion timestamp. If the determination is true, the computer system determines whether the move-out timestamp has an actual associated value and, if so, the computer system determines a second tablet in a second replication group in the database that includes the data item and issues the snapshot read operation to the second table in the second replication group to obtain a most-recent version of the data item that has a timestamp no greater than the snapshot timestamp T; otherwise, the computer system issues the snapshot read to the one tablet to obtain a most recent version of the data item that has a timestamp no greater than the snapshot timestamp T.
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