云计算的安全架构与技术_第7节.ppt

A library that is linked into every client One master server Assigning tablets to tablet servers Detecting the addition and deletion of tablet servers Balancing tablet-server load Garbage collection of files in GFS Many tablet servers Tablet servers manage tablets Tablet server splits tablets that get too big Client communicates directly with tablet server for reads/writes * Implementation: Three major components Tablet Location Since tablets move around from server to server, given a row, how do clients find the right machine? Need to find a tablet whose row range covers the target row * Tablet Location A 3-level hierarchy analogous to that of a B+-tree to store tablet location information A file stored in chubby contains location of the root tablet Root tablet contains location of Metadata tablets The root tablet never splits Each meta-data tablet contains the locations of a set of user tablets * Tablet Location Client reads the Chubby file that points to the root tablet This starts the location process Client library caches tablet locations Moves up the hierarchy if location N/A * Tablet Assignment * BigTable BigTable Master Performs metadata ops and load balancing BigTable Tablet Server BigTable Tablet Server Serves data Serves data Cluster scheduling system GFS Chubby Holds tablet data, logs Holds metadata, handles master election Handles failover, monitoring BigTable Client BigTable Client Library Tablet Server When a tablet server starts, it creates and acquires exclusive lock on, a uniquely-named file in a specific Chubby directory Call this servers directory A tablet server stops serving its tablets if it loses its exclusive lock This may happen if there is a network connection failure that causes the tablet server to lose its Chubby session * Tablet Server A tablet server will attempt to reacquire an exclusive lock on its file as long as the file still exists If the file no longer exists then the tablet server will n