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Show 53 Postgres does not employ logging. It has a "no-overwrite" storage manager. This means t hat no data is ever overwritten, rather all updates are turned into iJI S('rLions. 5.3.8 Concurrency OI>S('J·vcr has <-t vc 1y (kxib l<-' lucking scheme and no modi fication was needed to rlln mt il tiple cli ents. ESM a lso req uired only one minor change to support concurrency. Tbe locking gr anu larity in ESM is the page. By enclosing exclusive object a,ccesses for separate obj ects whi cb li<~ on tbe same page (false sharing) witb iu separate t ra nsactious, concu rrency was achieved. Postgres uses a standard two-p hase locking poli cy and sin ce objects belonging t o difFerent Alpba_l Ales are sL on~d in a. si11gle re la.Lion , conflicting concurrent execut ion could not occur. 5 .3 .9 Miscellaneous ObServer , ESM, and Postgres use the Un ix Socket interface (TCP / IP connec- 1io11 ) IH'twe( 'JI til(' (·liC'nt <LII rl tlw SI'I V<'r. In OhSen!(' r, t h<' rla L<thase file sys1<'1ll siz<' <-tJtd I h<' mapped segment memory W(~ re .') l\11 B. In SSM, hotb the server <tucl t he cli('nt h1dfer sizes are~ i\11 [l. Caching is not under user control i11 Postgres. Out of tlw Lh rc<o POSs, on ly Postgres provides security features. 5.4 Testbed Configuration A II tests were performed on J-1 PCJ000/ 7:30 workstat ions on an isolated Ethernet st 1b1wL . Tbe m achin <-~s w<-Te running OSF/ 1 1.0 exp.49, each configured witb ;32MB of' memory. The di sks used for t b f~ tests were 400 MB SCSI. The Unix fi le system was used for both data and log storage. More t han 10% of tbe disk space was free dming t lw tt>sts. |
