paper.ps

早期freebsd实现

97 672.96 R .236(uted source; instead, the)-.2 F 2.736(ys)-.15 G .236
(hould be placed on)463.472 672.96 R 3.845(as)97 690.96 S 1.345(ide branch.)
109.175 690.96 R 1.345(When the ne)6.345 F 1.345(xt softw)-.15 F 1.345
(are distrib)-.1 F 1.345(ution arri)-.2 F -.15(ve)-.25 G 1.344
(s, it should be appended to the trunk of the cus-).15 F(tomer')97 708.96 Q
3.172(sR)-.55 G .672(CS \214le, and the customer can then mer)136.842 708.96 R
.672(ge the local modi\214cations back into the ne)-.18 F 3.173(wr)-.25 G 3.173
(elease. In)483.674 708.96 R(the)3.173 E(abo)97 726.96 Q 2.204 -.15(ve ex)-.15
H 1.904(ample, a customer').15 F 4.404(sR)-.55 G 1.904(CS \214le w)228.866
726.96 R 1.904(ould contain the follo)-.1 F 1.904
(wing tree, assuming that the customer has)-.25 F EP
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/F0 10/Times-Roman@0 SF 272.71(PSD:13-6 RCS)72 54 R 2.5(\212AS)2.5 G
(ystem for V)435.84 54 Q(ersion Control)-1.11 E(recei)97 90 Q -.15(ve)-.25 G
2.727(dr).15 G -.25(ev)136.527 90 S .227
(ision 1.3, added his local modi\214cations as re).25 F .227
(vision 1.3.1.1, then recei)-.25 F -.15(ve)-.25 G 2.728(dr).15 G -.25(ev)
443.926 90 S .228(ision 2.4, and mer).25 F(ged)-.18 E
(2.4 and 1.3.1.1, resulting in 2.4.1.1.)97 108 Q 311.56 149.04 MT 0 -23.04 RL
-34.56 0 RL 0 23.04 RL CL .32 LW ST/F1 8/Times-Roman@0 SF(1.3)289.28 139.28 Q
484.36 149.04 MT 0 -23.04 RL -34.56 0 RL 0 23.04 RL CL ST(2.4)462.08 139.28 Q
449.8 137.52 311.56 137.52 DL 449.8 137.52 MT -4.608 1.152 RL 0 -2.304 RL CL BL
449.8 137.52 MT -4.608 1.152 RL 0 -2.304 RL CL ST 369.16 195.12 MT 0 -23.04 RL
-34.56 0 RL 0 23.04 RL CL ST(1.3.1.1)340.88 185.36 Q 334.6 183.6 294.28 149.04
DL 334.6 183.6 MT -4.248 -2.16 RL 1.512 -1.728 RL CL BL 334.6 183.6 MT -4.248
-2.16 RL 1.512 -1.728 RL CL ST 541.96 195.12 MT 0 -23.04 RL -34.56 0 RL 0 23.04
RL CL ST(2.4.1.1)513.68 185.36 Q 507.4 183.6 467.08 149.04 DL 507.4 183.6 MT
-4.248 -2.16 RL 1.512 -1.728 RL CL BL 507.4 183.6 MT -4.248 -2.16 RL 1.512
-1.728 RL CL ST F0(Figure 4.)194.605 213.12 Q 2.5(Ac)5 G(ustomer')249.875
213.12 Q 2.5(sr)-.55 G -.25(ev)294.595 213.12 S
(ision tree with local modi\214cations.).25 E .122
(This approach is actually practiced in the CSNET project, where se)97 249.12 R
-.15(ve)-.25 G .122(ral uni).15 F -.15(ve)-.25 G .122(rsities and a compan).15
F 2.622(yc)-.15 G(ooperate)505.57 249.12 Q(in de)97 267.12 Q -.15(ve)-.25 G
(loping a national computer netw).15 E(ork.)-.1 E/F2 10/Times-Italic@0 SF -.8
(Pa)72 288.72 S -.15(ra).8 G(llel de).15 E(velopment)-.15 E F0 1.249
(Sometimes it is desirable to e)97 306.72 R 1.249
(xplore an alternate design or a dif)-.15 F 1.25
(ferent implementation technique in parallel)-.25 F .217(with the main line de)
97 324.72 R -.15(ve)-.25 G 2.716(lopment. Such).15 F(de)2.716 E -.15(ve)-.25 G
.216(lopment should be carried out on a side branch.).15 F .216(The e)5.216 F
(xperimental)-.15 E(changes may later be mo)97 342.72 Q -.15(ve)-.15 G 2.5(di)
.15 G(nto the main line, or abandoned.)215.84 342.72 Q F2
(Con\215icting updates)72 364.32 Q F0 2.536(Ac)97 382.32 S .036
(ommon occurrence is that one programmer has check)111.196 382.32 R .036
(ed out a re)-.1 F .036(vision, b)-.25 F .037
(ut cannot complete the assignment)-.2 F 1.079(for some reason.)97 400.32 R
1.079(In the meantime, another person must perform another modi\214cation imme\
diately)6.079 F 6.078(.I)-.65 G 3.578(nt)516.422 400.32 S(hat)527.78 400.32 Q
.833(case, the second person should check-out the same re)97 418.32 R .833
(vision, modify it, and check it in on a side branch, for)-.25 F(later mer)97
436.32 Q(ging.)-.18 E(Ev)97 457.92 Q .316(ery node in a re)-.15 F .316
(vision tree consists of the follo)-.25 F .316(wing attrib)-.25 F .315
(utes: a re)-.2 F .315(vision number)-.25 F 2.815(,ac)-.4 G .315
(heck-in date and time,)450.185 457.92 R .425(the author')72 475.92 R 2.925(si)
-.55 G .425(denti\214cation, a log entry)125.07 475.92 R 2.925(,as)-.65 G .425
(tate and the actual te)240.145 475.92 R 2.926(xt. All)-.15 F .426
(these attrib)2.926 F .426(utes are determined at the time the)-.2 F(re)72
493.92 Q .378(vision is check)-.25 F .378(ed in.)-.1 F .377(The state attrib)
5.378 F .377(ute indicates the status of a re)-.2 F 2.877(vision. It)-.25 F
.377(is set automatically to `e)2.877 F(xperimental')-.15 E .535
(during check-in.)72 511.92 R 3.035(Ar)5.535 G -.25(ev)157.195 511.92 S .536
(ision can later be promoted to a higher status, for e).25 F .536
(xample `stable' or `released'.)-.15 F .536(The set of)5.536 F(states is user)
72 529.92 Q(-de\214ned.)-.2 E/F3 10/Times-Bold@0 SF 2.5(3.2. Re)72 565.92 R
(visions ar)-.15 E 2.5(er)-.18 G(epr)155.37 565.92 Q(esented as deltas)-.18 E
F0 -.15(Fo)97 587.52 S 3.252(rc).15 G .752(onserving space, RCS stores re)
118.432 587.52 R .752(visions in the form of deltas, i.e., as dif)-.25 F .752
(ferences between re)-.25 F 3.251(visions. The)-.25 F(user interf)72 605.52 Q
(ace completely hides this f)-.1 E(act.)-.1 E 2.767(Ad)97 627.12 S .267
(elta is a sequence of edit commands that transforms one string into another)
111.987 627.12 R 5.267(.T)-.55 G .268(he deltas emplo)427.918 627.12 R .268
(yed by RCS)-.1 F 1.188
(are line-based, which means that the only edit commands allo)72 645.12 R 1.188
(wed are insertion and deletion of lines.)-.25 F 1.187(If a single)6.187 F .333
(character in a line is changed, the edit scripts consider the entire line cha\
nged.)72 663.12 R .333(The program)5.333 F F2(dif)2.833 E(f)-.18 E F0(2)461.788
658.12 Q .334(produces a small,)469.622 663.12 R .705
(line-based delta between pairs of te)72 681.12 R .705(xt \214les.)-.15 F 3.205
(Ac)5.705 G(haracter)267.45 681.12 Q .705(-based edit script w)-.2 F .705
(ould tak)-.1 F 3.204(em)-.1 G .704(uch longer to compute, and)428.034 681.12 R
-.1(wo)72 699.12 S(uld not be signi\214cantly shorter).1 E(.)-.55 E EP
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/F0 10/Times-Roman@0 SF(RCS \212 A System for V)72 54 Q(ersion Control)-1.11 E
(PSD:13-7)500.55 54 Q 1.144(Using deltas is a classical space-time tradeof)97
90 R 1.145(f: deltas reduce the space consumed, b)-.25 F 1.145
(ut increase access time.)-.2 F(Ho)72 108 Q(we)-.25 E -.15(ve)-.25 G .879 -.4
(r, a v).15 H .078
(ersion control tool should impose as little delay as possible on programmers.)
.25 F(Excessi)5.078 E .378 -.15(ve d)-.25 H .078(elays discour).15 F(-)-.2 E
.422(age the use of v)72 126 R .422
(ersion controls, or induce programmers to tak)-.15 F 2.922(es)-.1 G .423
(hortcuts that compromise system inte)332.452 126 R(grity)-.15 E 5.423(.T)-.65
G 2.923(og)514.907 126 S(ain)527.78 126 Q 1.127(reasonably f)72 144 R 1.127(as\
t access time for both editing and compiling, RCS arranges deltas in the follo)
-.1 F 1.126(wing w)-.25 F(ay)-.1 E 6.126(.T)-.65 G 1.126(he most)507.484 144 R
.497(recent re)72 162 R .497(vision on the trunk is stored intact.)-.25 F .497
(All other re)5.497 F .498(visions on the trunk are stored as re)-.25 F -.15
(ve)-.25 G .498(rse deltas.).15 F 2.998(Ar)5.498 G -2.15 -.25(ev e)514.86 162 T
(rse).25 E .083(delta describes ho)72 180 R 2.583(wt)-.25 G 2.583(og)156.149
180 S 2.583(ob)168.732 180 S(ackw)181.315 180 Q .083(ard in the de)-.1 F -.15
(ve)-.25 G .083(lopment history: it produces the desired re).15 F .082
(vision if applied to the suc-)-.25 F .59(cessor of that re)72 198 R 3.09
(vision. This)-.25 F .59(implementation has the adv)3.09 F .59(antage that e)
-.25 F .59(xtraction of the latest re)-.15 F .59(vision is a simple and)-.25 F
-.1(fa)72 216 S .343(st cop).1 F 2.843(yo)-.1 G 2.843(peration. Adding)116.366
216 R 2.843(an)2.843 G .843 -.25(ew r)202.105 216 T -.25(ev).25 G .343
(ision to the trunk is also f).25 F(ast:)-.1 E/F1 10/Times-Italic@0 SF(ci)2.843
E F0 .343(simply adds the ne)2.843 F 2.843(wr)-.25 G -.25(ev)448.194 216 S .343
(ision intact, replaces).25 F .454(the pre)72 234 R .454(vious re)-.25 F .454
(vision with a re)-.25 F -.15(ve)-.25 G .454(rse delta, and k).15 F .454
(eeps the rest of the old deltas.)-.1 F(Thus,)5.454 E F1(ci)2.954 E F0 .454
(requires the computation of)2.954 F(only one ne)72 252 Q 2.5(wd)-.25 G(elta.)
133.13 252 Q 1.436(Branches need special treatment.)97 273.6 R 1.436(The nai)
6.436 F 1.735 -.15(ve s)-.25 H 1.435(olution w).15 F 1.435
(ould be to store complete copies for the tips of all)-.1 F 4.63
(branches. Clearly)72 291.6 R 4.63(,t)-.65 G 2.13(his approach w)155.87 291.6 R
2.131(ould cost too much space.)-.1 F 2.131(Instead, RCS uses)7.131 F F1
(forwar)4.631 E(d)-.37 E F0 2.131(deltas for branches.)4.631 F(Re)72 309.6 Q
.019(generating a re)-.15 F .019(vision on a side branch proceeds as follo)-.25
F 2.518(ws. First,)-.25 F -.15(ex)2.518 G .018(tract the latest re).15 F .018
(vision on the trunk; secondly)-.25 F(,)-.65 E .541(apply re)72 327.6 R -.15
(ve)-.25 G .541(rse deltas until the fork re).15 F .542
(vision for the branch is obtained; thirdly)-.25 F 3.042(,a)-.65 G .542
(pply forw)392.69 327.6 R .542(ard deltas until the desired)-.1 F .588
(branch re)72 345.6 R .588(vision is reached.)-.25 F .588
(Figure 5 illustrates a tree with one side branch.)5.588 F -.35(Tr)5.588 G .588
(iangles pointing to the left and right).35 F(represent re)72 363.6 Q -.15(ve)
-.25 G(rse and forw).15 E(ard deltas, respecti)-.1 E -.15(ve)-.25 G(ly).15 E(.)
-.65 E/F2 8/Times-Roman@0 SF(1.1)263.192 401.576 Q .32 LW 282.312 381.6 282.312
399.816 DL 252 399.816 282.312 381.6 DL 282.312 418.032 252 399.816 DL 282.312
399.744 282.312 417.96 DL 312.624 399.816 282.312 399.816 DL 312.624 399.816 MT
-6.048 1.512 RL 0 -3.024 RL CL BL 312.624 399.816 MT -6.048 1.512 RL 0 -3.024
RL CL ST(1.2)323.816 401.576 Q 342.936 381.6 342.936 399.816 DL 312.624 399.816
342.936 381.6 DL 342.936 418.032 312.624 399.816 DL 342.936 399.744 342.936
417.96 DL 373.248 399.816 342.936 399.816 DL 373.248 399.816 MT -6.048 1.512 RL
0 -3.024 RL CL BL 373.248 399.816 MT -6.048 1.512 RL 0 -3.024 RL CL ST(1.3)
384.44 401.576 Q 403.56 381.6 403.56 399.816 DL 373.248 399.816 403.56 381.6 DL
403.56 418.032 373.248 399.816 DL 403.56 399.744 403.56 417.96 DL 433.872
399.816 403.56 399.816 DL 433.872 399.816 MT -6.048 1.512 RL 0 -3.024 RL CL BL
433.872 399.816 MT -6.048 1.512 RL 0 -3.024 RL CL ST(2.1)445.064 401.576 Q
464.184 381.6 464.184 399.816 DL 433.872 399.816 464.184 381.6 DL 464.184
418.032 433.872 399.816 DL 464.184 399.744 464.184 417.96 DL 494.496 399.816
464.184 399.816 DL 494.496 399.816 MT -6.048 1.512 RL 0 -3.024 RL CL BL 494.496
399.816 MT -6.048 1.512 RL 0 -3.024 RL CL ST 540 414.936 MT 0 -30.312 RL
-45.504 0 RL 0 30.312 RL CL ST(2.2)512.248 401.576 Q(1.3.1.1)437.064 468.248 Q
433.872 484.704 464.184 466.488 DL 433.872 448.344 433.872 484.704 DL 464.184
466.488 433.872 448.272 DL 433.872 466.488 403.56 417.96 DL 433.872 466.488 MT
-4.464 -4.32 RL 2.592 -1.584 RL CL BL 433.872 466.488 MT -4.464 -4.32 RL 2.592
-1.584 RL CL ST 494.496 466.488 464.184 466.488 DL 494.496 466.488 MT -6.048
1.512 RL 0 -3.024 RL CL BL 494.496 466.488 MT -6.048 1.512 RL 0 -3.024 RL CL ST
(1.3.1.2)497.688 468.248 Q 494.496 484.704 524.808 466.488 DL 494.496 448.344
494.496 484.704 DL 524.808 466.488 494.496 448.272 DL F0(Figure 5.)190.57
502.704 Q 2.5(Ar)5 G -.25(ev)244.73 502.704 S(ision tree with re).25 E -.15(ve)
-.25 G(rse and forw).15 E(ard deltas.)-.1 E .241(Although implementing f)97
524.304 R .241(ast check-out for the latest trunk re)-.1 F .242
(vision, this arrangement has the disadv)-.25 F .242(antage that)-.25 F .295
(generation of other re)72 542.304 R .295(visions tak)-.25 F .294
(es time proportional to the number of deltas applied.)-.1 F -.15(Fo)5.294 G
2.794(re).15 G .294(xample, re)440.422 542.304 R .294(generating the)-.15 F
.469(branch tip in Figure 5 requires application of \214v)72 560.304 R 2.969
(ed)-.15 G .469(eltas \(including the initial one\).)280.209 560.304 R .469
(Since usage statistics sho)5.469 F 2.969(wt)-.25 G(hat)527.78 560.304 Q .915
(the latest trunk re)72 578.304 R .914(vision is the one that is retrie)-.25 F
-.15(ve)-.25 G 3.414(di).15 G 3.414(n9)285.472 578.304 S 3.414(5p)298.886
578.304 S .914(er cent of all cases \(see the section on usage statistics\),)
312.3 578.304 R .892(biasing check-out time in f)72 596.304 R -.2(avo)-.1 G
3.392(ro).2 G 3.393(ft)208.44 596.304 S .893(hat re)217.943 596.304 R .893
(vision results in signi\214cant sa)-.25 F 3.393(vings. Ho)-.2 F(we)-.25 E -.15
(ve)-.25 G 1.693 -.4(r, c).15 H .893(areful implementation of).4 F 1.622
(the delta application process is necessary to pro)72 614.304 R 1.621(vide lo)
-.15 F 4.121(wr)-.25 G(etrie)316.983 614.304 Q -.25(va)-.25 G 4.121(lo).25 G
-.15(ve)355.444 614.304 S 1.621(rhead for other re).15 F 1.621
(visions, in particular for)-.25 F(branch tips.)72 632.304 Q .965(There are se)
97 653.904 R -.15(ve)-.25 G .966(ral techniques for delta application.).15 F
.966(The nai)5.966 F 1.266 -.15(ve o)-.25 H .966
(ne is to pass each delta to a general-purpose).15 F(te)72 671.904 Q .228
(xt editor)-.15 F 5.228(.A)-.55 G .228(prototype of RCS in)130.034 671.904 R
-.2(vo)-.4 G -.1(ke).2 G 2.728(dt).1 G .227(he UNIX editor)240.806 671.904 R F1
(ed)2.727 E F0 .227(both for applying deltas and for e)2.727 F .227
(xpanding the identi\214-)-.15 F 1.122(cation mark)72 689.904 R 3.622
(ers. Although)-.1 F 1.122(easy to implement, performance w)3.622 F 1.122
(as poor)-.1 F 3.623(,o)-.4 G 1.123(wing to the high start-up costs and e)
365.919 689.904 R(xcess)-.15 E 1.163(generality of)72 707.904 R F1(ed)3.663 E
F0 6.163(.A)C 3.663(ni)152.969 707.904 S 1.163(ntermediate v)164.412 707.904 R
1.163(ersion of RCS used a special-purpose, stream-oriented editor)-.15 F 6.162
(.T)-.55 G 1.162(his technique)485.788 707.904 R .049(reduced the cost of appl\
ying a delta to the cost of checking out the latest trunk re)72 725.904 R 2.549
(vision. The)-.25 F .049(reason for this beha)2.549 F(vior)-.2 E EP
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/F0 10/Times-Roman@0 SF 272.71(PSD:13-8 RCS)72 54 R 2.5(\212AS)2.5 G
(ystem for V)435.84 54 Q(ersion Control)-1.11 E
(is that each delta application in)72 90 Q -.2(vo)-.4 G(lv).2 E
(es a complete pass o)-.15 E -.15(ve)-.15 G 2.5(rt).15 G(he preceding re)312.58
90 Q(vision.)-.25 E(Ho)97 111.6 Q(we)-.25 E -.15(ve)-.25 G 1.137 -.4(r, t).15 H
.337(here is a much better algorithm.).4 F .336
(Note that the deltas are line oriented and that most of the w)5.337 F .336
(ork of)-.1 F 2.865(as)72 129.6 S .365(tream editor in)83.195 129.6 R -.2(vo)
-.4 G(lv).2 E .365(es cop)-.15 F .365(ying unchanged lines from one re)-.1 F
.365(vision to the ne)-.25 F 2.866(xt. A)-.15 F -.1(fa)2.866 G .366
(ster algorithm a).1 F -.2(vo)-.2 G .366(ids unneces-).2 F .363(sary cop)72
147.6 R .362(ying of character strings by using a)-.1 F/F1 10/Times-Italic@0 SF
.362(piece table)2.862 F F0 5.362(.A)C .362
(piece table is a one-dimensional array)313.334 147.6 R 2.862(,s)-.65 G .362
(pecifying ho)475.096 147.6 R 2.862(wa)-.25 G(gi)72 165.6 Q -.15(ve)-.25 G