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Show 11 litlE'ar hashing ind ex. The linear hashing index can be used only for exact match queries whereas B+ tree index can also be used for range queries. All storage 1nanager information (objects, ii les , i nclices, and logs) is stored on a. volume which ( <lll he <t raw disk parti t ion or a. Unix file . To support ve rsioning, ESM provides copy-on-write (COW) objects. Objects can have eit her woTking or fTo zen versions. Clients can only modify woTI;;ing versions and 1ww ve rsion s c: a.n only he made of fnran versions. Once froz en, an object rna.y JJU L lw 111odified Lbougl: they Illd.Y lw uuf"rozen and tlwn mudihed. b~ SM's client inLPrface allows ilJ !pliccd,ion s to access and manipulate objects, flies , aucl indices. File operations are p erformed by the server. Object and iudex operations are performed by the client module in its own buffer pool. This contrasts wit l1 other client-serve r architectures where these operations are performed by the server. For thi s reason, tlw client bas its own lock cache, transaction information, and a 1 oggi ng su bsystcm. ESl\!1 's servPr is a rnulti-threaded process providing asynchronous I/0, file , trausctclion, concurrency control, and recovery services to multiple clients. If there are rnr1l t iple disk volumes, then a separate process manages each of them. 'I'hese disk 1/ 0 pmcesses read and write into th e server's builer pool which is in shared mernory. 2.5.~~ Gemstone C:f'IIJ'itonc [6] was dcv<·loped by Scrvio, Inc. It is oue of the earliest commercial OODBi\!lS. lt supports a model of objects similar to that of Srnalltalk-8 0. It bas lang li<tge interfaces to C, C++, and Small t alk . In Cemstone, ll1c OIDs a r<c rrnique long integers call ed Object Ori ented Pointers (OOP ). In-co re arid scconcl<try object tables arc used to map an OOP to an object's physical location on disk. A clustering facility is available for managing collections of objects ur sets of ins t ances . |
