数据库系统概念(database system concepts)英文第六版 课后练习题 答案 第10章

1、 File hasbeennopartial-write,buttheydifferincontent,thenwereplace2thecontentsoftherstblockwiththecontentsofthesecond,orviceversa.Thisrecoveryprocedureensuresthatawritetostablestorageeither succeeds completely (that is, updates both copies) or resultsin no change.The requirement of comparing every co

2、rresponding pair of blocksduringrecoveryisexpensivetomeet.Wecanreducethecostgreatlyby keeping track of block writes that are in progress, using a smallamount of nonvolatile RAM. On only blocks for whichwrites werein progressneed tobe compared.b. Theideaissimilarhere.Foranyblockwrite,theinformationbl

3、ockiswrittenrstfollowedbythecorrespondingparityblock.Atthetimeof each set consisting of the nthblock of each of the disksis considered. If none of the blocks in the set have been partially-written, and the parity block contents are consistent with the con-tentsoftheinformationblocks,thennofurtheract

4、ionneedbetaken.Ifanyblockhasbeenpartially-written,itscontentsarereconstructedusingtheotherblocks.Ifnoblockhasbeenpartially-written,buttheparity block contents do not agree with the information block con-tents, the parity blocks contents arereconstructed.10.4 Answer:a. Although moving record 6 to the

5、 space for 5, and moving record 7to the space for 6, is the most straightforward approach, it requiresmoving themost records,and involves the most accesses.b. Movingrecord7tothespacefor5movesfewerrecords,butdestroysany orderingin the le.c. Marking the space for 5 as deleted preserves ordering and mo

6、vesno records, but requires additional overhead to keep track of allof the free space in the le. This method may lead to too many“holes” in the le, which if not compacted from time to time, willaffect performance because of reduced availability of contiguousfreerecords.10.5 Answer: (Weuse “i” to den

7、ote a pointerto record“i”.)The originalle ofFigure10.7.Exercises3record0record1record2record3record4record5record6record7record8record9record10record1165000 44000095000 6Gold87000CalieriSinghCrickBrandtKim6200080000720009200080000a. The le after insert(24556, Turnamian,Finance, 98000).record0record1

8、record2record3record4record5record6record7record8record9record10record1165000980004000095000 687000CalieriSinghCrickBrandtKim6200080000720009200080000b. The le after delete record2. File 4record0record1record2record3record4record5record6record7record8record9record10record116500098000 495000 687000Ca

9、lieriSinghCrickBrandtKim6200080000720009200080000Thefreerecordchaincouldhavealternativelybeenfromtheheaderto 4,from 4 to 2,and nally from 2 to 6.c. The le after insert(34556, Thompson, Music,67000). 4record0record1record2record3record4record5record6record7record8record9record10record1165000980006700

10、095000 6Gold87000CalieriSinghCrickBrandtKim620008000072000920008000010.6 Answer:The relationsectionwith threetuples is as follows.coursesec1semesterFallbuildingPackardslot514H1Exercises5IDididyearCS-101CS-347CS-347CS-101FallFallFallFallAA-ACBIO-301CS-347CS-101CS-101CS-347BIO-301CS-101CS-347BIO-301BI

11、O-301BIO-301SummerFallFallFallFallSummerFallFallSummerSummerSummernullAFA-AnullAAnullnullnullThe multitable clusteringfor the above twoinstances can be taken as:BIO-301SummerPainterABIO-301BIO-301BIO-301BIO-301BIO-3011SummerSummerSummerSummerSummer2009nullnullnullnullnull1010012812345456785432176543

12、CS-34711111Fall20092009200920092009TaylorC10.7 Answer:a. Everytime a record is inserted/deleted, check if the usage of theblock has changed levels. In that case, update the corresponding File bits. Note that we dont need to access the bitmaps at all unless6the usage crosses a so in most of the cases

13、 there is nooverhead.b. When freespaceforalargerecordora setofrecordsissought,thenmultiple free list entries may have to be scanned before nding apropersized one,so overheadsaremuchhigher.Withbitmaps,onepage of bitmap can store free info for many pages, sospent forI/Onding free space is minimal. whe

14、n a whole block or alarge part of it is deleted, bitmap technique is more convenient forupdating freespace information.10.8 Answer: Hashtableisthecommonoptionforlargedatabasebuffers.Thehash function helps in locating the appropriate bucket, on which linearsearchis performed.10.9 Answer:a.is preferab

15、le towhere R 1 R is computed by using12a nested-loop processing strategy where each tuple in R must becomparedtoeachblockin R .Afterthersttupleof R isprocessed,the next needed block is the rst one in R . However, since it isthe least recently used, the2121buffermanagement strategy wouldreplacethat b

16、lock if a new block was needed bythe system.b.is preferable to where R 1 R is computed by sorting12the relations by join values and then comparing the values by pro-ceeding through the relations. Due to duplicate join values, it maybenecessaryto“back-up”inoneoftherelations.This “backing-up”could cross a block boundary into the most recently used block,wh