bdb_usenix.ps

介绍：MySQL是比较出名的数据库软件

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/F0 12/Times-Bold@0 SF 3(3.10.3. Checkpoints)79.2 84 R/F1 10
/Times-Roman@0 SF(Berk)79.2 100.2 Q(ele)-.1 E 6.085(yD)-.15 G 6.085(Bi)
-6.085 G 3.585(ncludes a checkpointing service that)-6.085 F .263
(interacts with the reco)79.2 112.2 R -.15(ve)-.15 G .263(ry system.).15
F .263(During normal pro-)5.263 F 2.415
(cessing, both the log and the database are changing)79.2 124.2 R
(continually)79.2 136.2 Q 5.925(.A)-.65 G 3.425(ta)-5.925 G 1.224 -.15
(ny g)-3.425 H -2.15 -.25(iv e).15 H 3.424(ni).25 G .924
(nstant, the on-disk v)-3.424 F(ersions)-.15 E .414(of the tw)79.2 148.2
R 2.914(oa)-.1 G .414(re not guaranteed to be consistent.)-2.914 F .414
(The log)5.414 F 3.838
(probably contains changes that are not yet in the)79.2 160.2 R
(database.)79.2 172.2 Q .085(When an application mak)79.2 188.4 R .086
(es a)-.1 F/F2 10/Times-Italic@0 SF -.15(ch)2.586 G(ec).15 E(kpoint)-.2
E F1 2.586(,a)C .086(ll committed)-2.586 F .443
(changes in the log up to that point are guaranteed to be)79.2 200.4 R
.631(present on the data disk, too.)79.2 212.4 R .632
(Checkpointing is moder)5.631 F(-)-.2 E .046(ately e)79.2 224.4 R
(xpensi)-.15 E .346 -.15(ve d)-.25 H .046(uring normal processing, b).15
F .045(ut limits the)-.2 F(time spent reco)79.2 236.4 Q -.15(ve)-.15 G
(ring from crashes.).15 E 3.117
(After an application or operating system crash, the)79.2 252.6 R(reco)
79.2 264.6 Q -.15(ve)-.15 G 7.419(ry system only needs to go back tw).15
F(o)-.1 E(checkpoints)79.2 278.6 Q/F3 7/Times-Roman@0 SF(1)-4 I F1 1.376
(to start rolling the log forw)3.876 4 N 3.875(ard. W)-.1 F(ithout)-.4 E
3.264(checkpoints, there is no w)79.2 290.6 R 3.265(ay to be sure ho)-.1
F 5.765(wl)-.25 G(ong)-5.765 E .395(restarting after a crash will tak)
79.2 302.6 R 2.895(e. W)-.1 F .395(ith checkpoints, the)-.4 F .088
(restart interv)79.2 314.6 R .089(al can be \214x)-.25 F .089
(ed by the programmer)-.15 F 5.089(.R)-.55 G(eco)-5.089 E(v-)-.15 E .668
(ery processing can be guaranteed to complete in a sec-)79.2 326.6 R
(ond or tw)79.2 338.6 Q(o.)-.1 E(Softw)79.2 354.8 Q 2.457
(are crashes are much more common than disk)-.1 F -.1(fa)79.2 366.8 S
3.385(ilures. Man).1 F 3.385(yd)-.15 G -2.15 -.25(ev e)-3.385 H .884
(lopers w).25 F .884(ant to guarantee that soft-)-.1 F -.1(wa)79.2 378.8
S .158(re b).1 F .158(ugs do not destro)-.2 F 2.658(yd)-.1 G .158
(ata, b)-2.658 F .158(ut are willing to restore)-.2 F .631
(from tape, and to tolerate a day or tw)79.2 390.8 R 3.131(oo)-.1 G
3.131(fl)-3.131 G .63(ost w)-3.131 F .63(ork, in)-.1 F .89(the unlikle)
79.2 402.8 R 3.39(ye)-.15 G -.15(ve)-3.64 G .89(nt of a disk crash.).15
F -.4(Wi)5.89 G .89(th Berk).4 F(ele)-.1 E 3.39(yD)-.15 G(B,)-3.39 E
1.093(programmers may truncate the log at checkpoints.)79.2 414.8 R(As)
6.092 E .09(long as the tw)79.2 426.8 R 2.59(om)-.1 G .09
(ost recent checkpoints are present, the)-2.59 F(reco)79.2 438.8 Q -.15
(ve)-.15 G .106(ry system can guarantee that no committed trans-).15 F
.611(actions are lost after a softw)79.2 450.8 R .611(are crash.)-.1 F
.611(In this case, the)5.611 F(reco)79.2 462.8 Q -.15(ve)-.15 G 1.439
(ry system does not require that the log and the).15 F 1.328
(data be on separate de)79.2 474.8 R 1.329
(vices, although separating them)-.25 F(can still impro)79.2 486.8 Q .3
-.15(ve p)-.15 H(erformance by spreading out writes.).15 E F0 3
(3.10.4. T)79.2 516.8 R -.12(wo)-.888 G(-phase locking).12 E F1(Berk)
79.2 533 Q(ele)-.1 E 4.416(yD)-.15 G 4.416(Bp)-4.416 G(ro)-4.416 E 1.916
(vides a service kno)-.15 F 1.915(wn as tw)-.25 F(o-phase)-.1 E 3.017
(locking. In)79.2 545 R .517(order to reduce the lik)3.017 F .518
(elihood of deadlocks)-.1 F 2.547(and to guarantee A)79.2 557 R 2.546
(CID properties, database systems)-.4 F .063(manage locks in tw)79.2 569
R 2.564(op)-.1 G 2.564(hases. First,)-2.564 F .064(during the operation)
2.564 F 1.574(of a transaction, the)79.2 581 R 4.074(ya)-.15 G 1.574
(cquire locks, b)-4.074 F 1.573(ut ne)-.2 F -.15(ve)-.25 G 4.073(rr).15
G(elease)-4.073 E 6.147(them. Second,)79.2 593 R 3.648
(at the end of the transaction, the)6.147 F(y)-.15 E .235
(release locks, b)79.2 605 R .235(ut ne)-.2 F -.15(ve)-.25 G 2.735(ra)
.15 G .235(cquire them.)-2.735 F .235(In practice, most)5.235 F 4.69
(database systems, including Berk)79.2 617 R(ele)-.1 E 7.19(yD)-.15 G
4.69(B, acquire)-7.19 F 2.314(locks on demand o)79.2 629 R -.15(ve)-.15
G 4.814(rt).15 G 2.314(he course of the transaction,)-4.814 F
(then \215ush the log, then release all locks.)79.2 641 Q .32 LW 83.2
650.6 79.2 650.6 DL 87.2 650.6 83.2 650.6 DL 91.2 650.6 87.2 650.6 DL
95.2 650.6 91.2 650.6 DL 99.2 650.6 95.2 650.6 DL 103.2 650.6 99.2 650.6
DL 107.2 650.6 103.2 650.6 DL 111.2 650.6 107.2 650.6 DL 115.2 650.6
111.2 650.6 DL 119.2 650.6 115.2 650.6 DL 123.2 650.6 119.2 650.6 DL
127.2 650.6 123.2 650.6 DL 131.2 650.6 127.2 650.6 DL 135.2 650.6 131.2
650.6 DL 139.2 650.6 135.2 650.6 DL 143.2 650.6 139.2 650.6 DL 147.2
650.6 143.2 650.6 DL 151.2 650.6 147.2 650.6 DL 155.2 650.6 151.2 650.6
DL 159.2 650.6 155.2 650.6 DL 163.2 650.6 159.2 650.6 DL 167.2 650.6
163.2 650.6 DL 171.2 650.6 167.2 650.6 DL 175.2 650.6 171.2 650.6 DL
179.2 650.6 175.2 650.6 DL 183.2 650.6 179.2 650.6 DL 187.2 650.6 183.2
650.6 DL 191.2 650.6 187.2 650.6 DL 195.2 650.6 191.2 650.6 DL 199.2
650.6 195.2 650.6 DL 203.2 650.6 199.2 650.6 DL 207.2 650.6 203.2 650.6
DL 211.2 650.6 207.2 650.6 DL 215.2 650.6 211.2 650.6 DL 219.2 650.6
215.2 650.6 DL 223.2 650.6 219.2 650.6 DL/F4 5/Times-Roman@0 SF(1)100.8
661 Q/F5 8/Times-Roman@0 SF .338(One checkpoint is not f)2.338 3.2 N
.338(ar enough.)-.08 F .338(The reco)4.338 F -.12(ve)-.12 G .338
(ry system can-).12 F .211
(not be sure that the most recent checkpoint completed \212 it may ha)
79.2 673.8 R -.12(ve)-.16 G .734
(been interrupted by the crash that forced the reco)79.2 683.4 R -.12
(ve)-.12 G .734(ry system to run).12 F(in the \214rst place.)79.2 693 Q
F1(Berk)323.2 84 Q(ele)-.1 E 3.306(yD)-.15 G 3.306(Bc)-3.306 G .806
(an lock entire database \214les, which cor)-3.306 F(-)-.2 E .845
(respond to tables, or indi)323.2 96 R .844(vidual pages in them.)-.25 F
.844(It does)5.844 F 2.141(no record-le)323.2 108 R -.15(ve)-.25 G 4.641
(ll).15 G 4.641(ocking. By)-4.641 F 2.142(shrinking the page size,)4.641
F(ho)323.2 120 Q(we)-.25 E -.15(ve)-.25 G 4.427 -.4(r, d).15 H -2.15
-.25(ev e).4 H 3.627(lopers can guarantee that e).25 F -.15(ve)-.25 G
3.626(ry page).15 F 2.101(holds only a small number of records.)323.2
132 R 2.102(This reduces)7.102 F(contention.)323.2 144 Q .388
(If locking is enabled, then read and write operations on)323.2 160.2 R
5.317(ad)323.2 172.2 S 2.817(atabase acquire tw)-5.317 F 2.817
(o-phase locks, which are held)-.1 F 3.635
(until the transaction completes.)323.2 184.2 R 3.635(Which objects are)
8.635 F(lock)323.2 196.2 Q .738
(ed and the order of lock acquisition depend on the)-.1 F -.1(wo)323.2
208.2 S .503(rkload for each transaction.).1 F .502
(It is possible for tw)5.502 F 3.002(oo)-.1 G(r)-3.002 E 1.315
(more transactions to deadlock, so that each is w)323.2 220.2 R(aiting)
-.1 E(for a lock that is held by another)323.2 232.2 Q(.)-.55 E(Berk)
323.2 248.4 Q(ele)-.1 E 3.307(yD)-.15 G 3.307(Bd)-3.307 G .807
(etects deadlocks and automatically rolls)-3.307 F 1.825
(back one of the transactions.)323.2 260.4 R 1.825
(This releases the locks)6.825 F 1.926(that it held and allo)323.2 272.4
R 1.925(ws the other transactions to con-)-.25 F 3.346(tinue. The)323.2
284.4 R .847(caller is noti\214ed that its transaction did not)3.346 F
1.747(complete, and may restart it.)323.2 296.4 R(De)6.747 E -.15(ve)
-.25 G 1.747(lopers can specify).15 F .646
(the deadlock detection interv)323.2 308.4 R .647(al and the polic)-.25
F 3.147(yt)-.15 G 3.147(ou)-3.147 G .647(se in)-3.147 F
(choosing a transaction to roll back.)323.2 320.4 Q 6.686(The tw)323.2
336.6 R 6.686(o-phase locking interf)-.1 F 6.686(aces are separately)-.1
F .927(callable by applications that link Berk)323.2 348.6 R(ele)-.1 E
3.427(yD)-.15 G .928(B, though)-3.427 F(fe)323.2 360.6 Q 5.64(wu)-.25 G
3.14(sers ha)-5.64 F 3.44 -.15(ve n)-.2 H 3.14(eeded to use that f).15 F
3.14(acility directly)-.1 F(.)-.65 E 2.211(Using these interf)323.2
372.6 R 2.211(aces, Berk)-.1 F(ele)-.1 E 4.711(yD)-.15 G 4.712(Bp)-4.711
G(ro)-4.712 E 2.212(vides a f)-.15 F(ast,)-.1 E 2.4
(platform-portable locking system for general-purpose)323.2 384.6 R
2.917(use. It)323.2 396.6 R .418
(also lets users include non-database objects in a)2.917 F 3.497
(database transaction, by controlling access to them)323.2 408.6 R -.15
(ex)323.2 420.6 S(actly as if the).15 E 2.5(yw)-.15 G
(ere inside the database.)-2.5 E .583(The Berk)323.2 436.8 R(ele)-.1 E
3.083(yD)-.15 G 3.084(Bt)-3.083 G -.1(wo)-3.084 G .584(-phase locking f)
.1 F .584(acility is b)-.1 F .584(uilt on)-.2 F .609(the f)323.2 448.8 R
.609(astest correct locking primiti)-.1 F -.15(ve)-.25 G 3.108(st).15 G
.608(hat are supported)-3.108 F 1.967(by the underlying architecture.)
323.2 460.8 R 1.967(In the current imple-)6.967 F .593
(mentation, this means that the locking system is dif)323.2 472.8 R(fer)
-.25 E(-)-.2 E 1.709(ent on the v)323.2 484.8 R 1.709
(arious UNIX platforms, and is still more)-.25 F(dif)323.2 496.8 Q .695
(ferent on W)-.25 F(indo)-.4 E .695(ws NT)-.25 F 5.695(.I)-.74 G 3.195
(no)-5.695 G .695(ur e)-3.195 F .695(xperience, the most)-.15 F(dif)
323.2 508.8 Q 2.634
(\214cult aspect of performance tuning is \214nding the)-.25 F -.1(fa)
323.2 520.8 S .883(stest locking primiti).1 F -.15(ve)-.25 G 3.383(st)
.15 G .883(hat w)-3.383 F .882(ork correctly on a par)-.1 F(-)-.2 E 1.26
(ticular architecture and then inte)323.2 532.8 R 1.26(grating the ne)
-.15 F 3.76(wi)-.25 G(nter)-3.76 E(-)-.2 E -.1(fa)323.2 544.8 S
(ce with the se).1 E -.15(ve)-.25 G(ral that we already support.).15 E
.536(The w)323.2 561 R .536(orld w)-.1 F .536
(ould be a better place if the operating sys-)-.1 F 2.096
(tems community w)323.2 573 R 2.096(ould uniformly implement POSIX)-.1 F
1.31(locking primiti)323.2 585 R -.15(ve)-.25 G 3.81(sa).15 G 1.31(nd w)
-3.81 F 1.31(ould guarantee that acquiring)-.1 F 1.085
(an uncontested lock w)323.2 597 R 1.085(as a f)-.1 F 1.085
(ast operation.)-.1 F 1.085(Locks must)6.085 F -.1(wo)323.2 609 S 3.641
(rk both among threads in a single process and).1 F(among processes.)
323.2 621 Q F0 3(3.11. Concurr)323.2 651 R(ency)-.216 E F1 .383
(Good performance under concurrent operation is a crit-)323.2 667.2 R
.766(ical design point for Berk)323.2 679.2 R(ele)-.1 E 3.266(yD)-.15 G
3.265(B. Although)-3.266 F(Berk)3.265 E(ele)-.1 E(y)-.15 E 1.961
(DB is itself not multi-threaded, it is thread-safe, and)323.2 691.2 R
.547(runs well in threaded applications.)323.2 703.2 R(Philosophically)
5.546 E 3.046(,w)-.65 G(e)-3.046 E(vie)323.2 715.2 Q 4.764(wt)-.25 G
2.264(he use of threads and the choice of a threads)-4.764 F EP
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/F0 10/Times-Roman@0 SF .066(package as a polic)79.2 84 R 2.566(yd)-.15
G .065(ecision, and prefer to of)-2.566 F .065(fer mecha-)-.25 F .042
(nism \(the ability to run threaded or not\), allo)79.2 96 R .043
(wing appli-)-.25 F(cations to choose their o)79.2 108 Q(wn policies.)
-.25 E 1.947(The locking, logging, and b)79.2 124.2 R(uf)-.2 E 1.947
(fer pool subsystems all)-.25 F .711
(use shared memory or other OS-speci\214c sharing f)79.2 136.2 R(acili-)
-.1 E 1.713(ties to communicate.)79.2 148.2 R 1.713(Locks, b)6.713 F(uf)
-.2 E 1.713(fer pool fetches, and)-.25 F 1.061(log writes beha)79.2
160.2 R 1.361 -.15(ve i)-.2 H 3.561(nt).15 G 1.061(he same w)-3.561 F
1.061(ay across threads in a)-.1 F .033(single process as the)79.2 172.2
R 2.532(yd)-.15 G 2.532(oa)-2.532 G .032(cross dif)-2.532 F .032
(ferent processes on a)-.25 F(single machine.)79.2 184.2 Q .896
(As a result, concurrent database applications may start)79.2 200.4 R
1.651(up a ne)79.2 212.4 R 4.151(wp)-.25 G 1.651(rocess for e)-4.151 F
-.15(ve)-.25 G 1.651(ry single user).15 F 4.151(,m)-.4 G 1.651
(ay create a)-4.151 F 2.848(single serv)79.2 224.4 R 2.848(er which spa)
-.15 F 2.849(wns a ne)-.15 F 5.349(wt)-.25 G 2.849(hread for e)-5.349 F
-.15(ve)-.25 G(ry).15 E(client request, or may choose an)79.2 236.4 Q
2.5(yp)-.15 G(olic)-2.5 E 2.5(yi)-.15 G 2.5(nb)-2.5 G(etween.)-2.5 E
(Berk)79.2 252.6 Q(ele)-.1 E 3.629(yD)-.15 G 3.629(Bh)-3.629 G 1.128
(as been carefully designed to minimize)-3.629 F .07
(contention and maximize concurrenc)79.2 264.6 R 3.87 -.65(y. T)-.15 H
.07(he cache man-).65 F .57(ager allo)79.2 276.6 R .57
(ws all threads or processes to bene\214t from I/O)-.25 F 2.917
(done by one.)79.2 288.6 R 2.917(Shared resources must sometimes be)
7.917 F(lock)79.2 300.6 Q 1.804(ed for e)-.1 F(xclusi)-.15 E 2.104 -.15
(ve a)-.25 H 1.804(ccess by one thread of control.).15 F 1.757 -.8(We h)
79.2 312.6 T -2.25 -.2(av e).8 H -.1(ke)2.857 G .158
(pt critical sections small, and are careful not).1 F 1.199
(to hold critical resource locks across system calls that)79.2 324.6 R
.538(could deschedule the locking thread or process.)79.2 336.6 R
(Sleep-)5.539 E .979(ycat Softw)79.2 348.6 R .979
(are has customers with hundreds of concur)-.1 F(-)-.2 E(rent users w)
79.2 360.6 Q(orking on a single database in production.)-.1 E/F1 12
/Times-Bold@0 SF 3(4. Engineering)79.2 390.6 R(Philosoph)3 E(y)-.18 E F0
(Fundamentally)79.2 406.8 Q 3.998(,B)-.65 G(erk)-3.998 E(ele)-.1 E 3.998
(yD)-.15 G 3.998(Bi)-3.998 G 3.999(sac)-3.998 G 1.499
(ollection of access)-3.999 F .19(methods with important f)79.2 418.8 R
.19(acilities, lik)-.1 F 2.69(el)-.1 G .19(ogging, locking,)-2.69 F
1.251(and transactional access underlying them.)79.2 430.8 R 1.252
(In both the)6.252 F .992(research and the commercial w)79.2 442.8 R
.991(orld, the techniques for)-.1 F -.2(bu)79.2 454.8 S 2.727
(ilding systems lik).2 F 5.227(eB)-.1 G(erk)-5.227 E(ele)-.1 E 5.227(yD)
-.15 G 5.227(Bh)-5.227 G -2.25 -.2(av e)-5.227 H 2.728(been well-)5.427
F(kno)79.2 466.8 Q(wn for a long time.)-.25 E .443(The k)79.2 483 R .743
-.15(ey a)-.1 H(dv).15 E .442(antage of Berk)-.25 F(ele)-.1 E 2.942(yD)
-.15 G 2.942(Bi)-2.942 G 2.942(st)-2.942 G .442(he careful atten-)-2.942
F 1.059(tion that has been paid to engineering details through-)79.2 495
R 1.039(out its life.)79.2 507 R 2.639 -.8(We h)6.039 H -2.25 -.2(av e)
.8 H 1.039(carefully designed the system so)3.739 F .452
(that the core f)79.2 519 R .452(acilities, lik)-.1 F 2.952(el)-.1 G
.452(ocking and I/O, surf)-2.952 F .453(ace the)-.1 F .972(right interf)
79.2 531 R .971(aces and are otherwise opaque to the caller)-.1 F(.)-.55
E .294(As programmers, we understand the v)79.2 543 R .295
(alue of simplicity)-.25 F .206(and ha)79.2 555 R .506 -.15(ve w)-.2 H
(ork).05 E .206(ed hard to simplify the interf)-.1 F .205(aces we sur)
-.1 F(-)-.2 E -.1(fa)79.2 567 S(ce to users of the database system.).1 E
(Berk)79.2 583.2 Q(ele)-.1 E 4.531(yD)-.15 G 4.531(Ba)-4.531 G -.2(vo)
-4.731 G 2.031(