数据库系统

开发平台：

Unix_Linux

internals.ps：源码内容

y(char)h(*result;)318 3131 y(if)g((complex)g(==)h(NULL))f
(return(NULL);)318 3190 y(result)g(=)h((char)f(*))h(palloc(60);)
318 3250 y(sprintf(result,)e("(45g,45g)",)h(complex->x,)f
(complex->y);)318 3310 y(return(result);)258 3370
y(})p eop
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38 37 bop 270 60 a Ft(38)310 b Fm(CHAPTER)14 b(2.)25
b(POSTGRESQL)13 b(FR)n(OM)f(THE)i(USER'S)e(POINT)g(OF)g(VIEW)270
234 y Ft(Note)h(that)g(the)g(functions)g(de02ned)g(abo)o(v)o(e)h
(operate)f(on)g(types)g(that)g(require)g Fp(pass)g(by)h(r)n(efer)n
(ence)p Ft(.)20 b(The)270 294 y(functions)c(take)h(a)g(pointer)f(to)h
(the)g(data)g(as)h(ar)o(gument)e(and)h(return)f(a)i(pointer)e(to)h(the)
g(deri)o(v)o(ed)f(data)270 354 y(instead)h(of)g(passing)g(and)g
(returning)e(the)i(data)g(itself.)29 b(That')m(s)18 b(why)e(we)h(ha)o
(v)o(e)g(to)g(reserv)o(e)g(memory)270 413 y(using)f Fr(palloc)f
Ft(within)g(the)h(functions.)26 b((If)14 b(we)i(would)f(just)h
(de02ne)f(a)h(local)g(v)o(ariable)f(and)h(return)270
473 y(the)e(addresses)h(of)f(these)h(v)o(ariables)f(the)g(system)h
(would)e(fail,)i(because)g(the)f(memory)f(used)i(by)f(local)270
533 y(v)o(ariables)e(is)h(freed)e(when)i(the)f(function)g(de02ning)f
(these)i(v)o(ariables)f(completes.))345 593 y(The)e(ne)o(xt)g(step)g
(is)g(to)g(compile)f(the)h(C-functions)f(and)h(create)f(the)h(shared)g
(library)f Fr(complex.so)p Ft(.)270 653 y(This)h(is)g(done)f(in)g(the)h
(way)f(described)g(in)h(the)f(pre)o(vious)g(section)g
Fp(Pr)n(ogr)o(amming)h(Language)e(Functions)270 712 y
Ft(and)j(depends)g(on)g(the)g(system)h(you)f(are)g(using.)k(On)c(a)g
(Linux)g(ELF)h(system)g(using)f Fr(gcc)f Ft(it)h(would)f(look)270
772 y(like)i(this:)330 868 y Fr($)30 b(gcc)f(-I$PGROOT/include)f(-fpic)
h(-c)60 b(complex.c)29 b(-o)h(complex.o)330 928 y($)g(gcc)f(-shared)g
(-o)h(complex.so)f(complex.o)270 1023 y Ft(No)o(w)11
b(we)h(are)f(ready)g(to)g(de02ne)h(the)f(ne)o(w)g(datatype)g(b)o(ut)g
(before)g(that)g(we)h(ha)o(v)o(e)g(to)f(make)g(the)g
Fp(input)g Ft(and)270 1083 y Fp(output)h(function)g Ft(kno)o(wn)f(to)i
(PostgreSQL:)330 1179 y Fr(testdb=>)29 b(create)g(function)g
(complex_in(opaque))330 1238 y(testdb->)g(returns)g(complex)330
1298 y(testdb->)g(as)g('/<where_ever_you_put_it>/complex.so)o(')330
1358 y(testdb->)g(language)g('c';)330 1418 y(NOTICE:)59
b(ProcedureCreate:)28 b(type)h('complex')g(is)h(not)599
1477 y(yet)f(defined)330 1537 y(CREATE)330 1597 y(testdb=>)g(create)g
(function)g(complex_out(opaque))330 1657 y(testdb->)g(returns)g
(opaque)330 1717 y(testdb->)g(as)g
('/<where_ever_you_put_it>/complex.so)o(')330 1776 y(testdb->)g
(language)g('c';)330 1836 y(CREATE)330 1896 y(testdb=>)g(create)g(type)
g(complex)h(()330 1956 y(testdb->)f(internallength)f(=)i(16,)330
2015 y(testdb->)f(input)g(=)h(complex_in,)330 2075 y(testdb->)f(output)
g(=)h(complex_out)330 2135 y(testdb->)f();)330 2195
y(CREATE)330 2255 y(testdb=>)270 2350 y Ft(Note)37 b(that)f(the)h(ar)o
(gument)f(type)h(gi)o(v)o(en)f(in)h(the)f(de02nition)g(of)h
Fr(complex)p 1798 2350 15 2 v 17 w(out())f Ft(and)270
2410 y Fr(complex)p 483 2410 V 17 w(in())28 b Ft(-)g
Fr(opaque)f Ft(-)h(is)h(needed)f(by)g(PostgreSQL)g(to)g(be)g(able)g(to)
g(pro)o(vide)g(an)270 2470 y(uniform)14 b(mechanism)i(for)f(the)h
(de02nition)e(of)i(the)f Fp(input)h Ft(and)f Fp(output)g(functions)h
Ft(needed)g(by)f(a)h(ne)o(w)270 2530 y(data)k(type.)40
b(It)20 b(is)h(not)f(necessary)h(to)f(specify)h(the)f(e)o(xact)h(type)f
(of)g(the)h(ar)o(guments)f(gi)o(v)o(en)g(to)g(the)270
2589 y(functions.)34 b(The)19 b Fp(input)f(function)g
Ft(is)h(ne)o(v)o(er)f(called)g(e)o(xplicitly)g(and)h(when)g(it)f(is)h
(called)f(implicitly)270 2649 y((e.g.)24 b(by)15 b(a)g(statement)h
(like)e Fr(insert)29 b(into)p Ft())15 b(it)f(is)i(clear)f(that)g(a)g
(character)g(string)f((i.e.)25 b(a)15 b(part)g(of)270
2709 y(the)h Fp(insert)h Ft(query))e(will)g(be)i(passed)g(to)f(it.)26
b(The)17 b Fp(output)e(function)h Ft(is)g(only)g(called)g(()g(by)g(an)
g(internal)270 2769 y(mechanism)h(of)g(PostgreSQL))g(when)g(data)g(of)
g(the)g(corresponding)g(user)g(de02ned)g(type)g(has)h(to)f(be)270
2828 y(displayed.)32 b(In)18 b(this)g(case)h(it)e(is)h(also)h(clear)e
(that)h(the)g(input)f(is)i(of)e(the)h(type)g(used)g(for)f(the)h
(internal)270 2888 y(representation)12 b((e.g.)k Fr(complex)p
Ft().)e(The)f(output)f(is)h(of)f(type)g(character)g(string.)270
3008 y(The)h(ne)o(w)f(type)g(can)h(no)o(w)f(be)g(used)h(as)g(if)f(it)g
(were)g(another)g(base)h(type:)330 3103 y Fr(testdb=>)29
b(create)g(table)g(complex_test)330 3163 y(testdb->)g((val)g
(complex);)330 3223 y(CREATE)330 3283 y(testdb=>)g(insert)g(into)g
(complex_test)330 3342 y(testdb->)g((val))g(values)g(('(1,2)');)
330 3402 y(INSERT)59 b(155872)29 b(1)p eop
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39 38 bop 198 60 a Fm(2.5.)29 b(SOME)12 b(OF)h(POSTGRESQL)-5
b('S)12 b(SPECIAL)h(FEA)-6 b(TURES)14 b(IN)e(DET)-5 b(AIL)340
b Ft(39)258 234 y Fr(testdb=>)29 b(insert)g(into)g(complex_test)258
294 y(testdb->)g((val))g(values)g(('(3,4)');)258
354 y(INSERT)59 b(155873)29 b(1)258 413 y(testdb=>)g(insert)g(into)g
(complex_test)258 473 y(testdb->)g((val))g(values)g(('(5,6)');)
258 533 y(INSERT)59 b(155874)29 b(1)258 653 y(testdb=>)g(select)g(*)h
(from)f(complex_test;)318 712 y(val)258 772 y(-----)258
832 y((1,2))258 892 y((3,4))258 951 y((5,6))258
1011 y((3)g(rows))258 1131 y(testdb=>)198 1272 y Fh(2.5.4)59
b(Extending)15 b(Operators)198 1365 y Ft(So)i(far)g(we)g(are)h(able)f
(to)h(de02ne)f(a)h(ne)o(w)f(type,)i(create)f(tables)f(that)h(use)g
(the)f(ne)o(w)g(type)h(for)e(one)i((or)198 1425 y(more))13
b(attrib)o(ute(s))g(and)g(populate)h(the)g(ne)o(w)g(tables)g(with)f
(data.)21 b(W)l(e)14 b(are)g(also)g(able)g(to)g(retrie)o(v)o(e)f(data)
198 1485 y(from)d(those)h(tables)h(as)g(long)e(as)i(we)f(do)g(not)g
(use)h(the)f(ne)o(w)g(data)g(types)h(within)e(the)h(quali02cation)f
(of)h(the)198 1544 y(query)m(.)23 b(If)14 b(we)h(want)f(to)h(use)g(the)
g(ne)o(w)g(data)g(types)g(in)g(the)g Fr(where)f Ft(clause)i(we)f(ha)o
(v)o(e)g(to)g(adapt)g(some)198 1604 y((or)d(all))f(of)h(the)h
(operators.)198 1718 y Fn(Example)g(2.9)25 b Ft(W)l(e)10
b(sho)o(w)h(ho)o(w)f(the)g(operator)g('=')g(can)g(be)h(adapted)f(for)g
(the)g(usage)h(on)f(the)h Fr(complex)198 1778 y Ft(data)17
b(type)g(de02ned)g(in)f(section)i(2.5.3)f Fp(User)h(De02ned)f(T)l
(ypes)p Ft(.)31 b(W)l(e)17 b(need)g(a)g(user)g(de02ned)g(function)198
1838 y Fr(complex)p 411 1838 15 2 v 17 w(cmp(complex,complex))10
b Ft(that)j(returns)f Fr(true)g Ft(if)g(the)g(comple)o(x)g(numbers)g
(gi)o(v)o(en)198 1898 y(as)g(ar)o(guments)g(are)g(equal)f(and)h
Fr(false)g Ft(otherwise.)j(This)d(function)f(is)h(de02ned)g(as)g
(described)g(in)g(sec-)198 1957 y(tion)h(2.5.2)i Fp(User)f(De02ned)g
(Functions)p Ft(.)20 b(In)13 b(our)g(case)h(there)g(are)f(already)g
(two)g(functions)g(present)h(for)198 2017 y(the)f(usage)h(of)f(type)h
Fr(complex)e Ft(-the)h Fp(input)g Ft(and)h Fp(output)f(function)f
Ft(de02ned)i(in)f(e)o(xample)g(2.8.)20 b(So)13 b(we)198
2077 y(can)k(add)f(the)h(ne)o(w)f(function)f Fr(complex)p
943 2077 V 18 w(cmp(complex,complex))f Ft(by)i(simply)g(appending)198
2137 y(the)c(follo)o(wing)f(lines)i(to)f(the)g(02le)g
Fr(complex.c)g Ft(gi)o(v)o(en)g(in)g(e)o(xample)h(2.8:)258
2229 y Fr(/*)29 b(Comparison)g(Function)g(*/)258 2289
y(/*)g(returns)h(true)f(if)h(arg1)f(and)h(arg2)f(are)h(equal)f(*/)258
2348 y(bool)g(complex_cmp(Complex)f(*arg1,)h(Complex)g(*arg2))258
2408 y({)318 2468 y(if((arg1->x)f(==)i(arg2->x))f(&&)407
2528 y((arg1->y)g(==)h(arg2->y)))318 2588 y({)377
2647 y(return)g(true;)318 2707 y(})318 2767 y(else)318
2827 y({)377 2886 y(return)g(false;)318 2946 y(})258
3006 y(})198 3098 y Ft(No)o(w)12 b(we)h(create)f(the)g(shared)h
(library)e(again:)258 3190 y Fr($)30 b(gcc)f(-I$PGROOT/include)f(-fpic)
h(-c)60 b(complex.c)29 b(-o)h(complex.o)258 3250 y($)g(gcc)f(-shared)g
(-o)h(complex.so)f(complex.o)198 3342 y Ft(Note)10 b(that)f(all)h(the)f
(functions)h(de02ned)f(in)h Fr(complex.c)e Ft(()p
Fr(complex)p 1428 3342 V 17 w(in(),)29 b(complex)p
1834 3342 V 18 w(out())198 3402 y Ft(and)12 b Fr(complex)p
495 3402 V 18 w(cmp())p Ft())f(are)h(no)o(w)g(contained)g(in)h(the)f
(shared)g(library)g Fr(complex.so)p Ft(.)p eop
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40 39 bop 270 60 a Ft(40)307 b Fm(CHAPTER)14 b(2.)28
b(POSTGRESQL)13 b(FR)n(OM)f(THE)i(USER'S)e(POINT)g(OF)g(VIEW)270
234 y Ft(No)o(w)k(we)h(make)g(the)f(ne)o(w)h(function)f(kno)o(wn)g(to)h
(PostgreSQL)f(and)h(after)f(that)h(we)g(de02ne)f(the)h(ne)o(w)270
294 y(operator)11 b('=')h(for)g(the)g Fr(complex)g Ft(type:)330
394 y Fr(testdb=>)29 b(create)g(function)g
(complex_cmp(complex,complex))330 454 y(testdb->)g(returns)g(complex)
330 513 y(testdb->)g(as)g('/<where_ever_you_put_it>/complex.so)o(')330
573 y(testdb->)g(language)g('c';)330 633 y(CREATE)330
693 y(testdb=>)g(create)g(operator)g(=)h(()330 753 y(testdb->)f
(leftarg)g(=)h(complex,)330 812 y(testdb->)f(rightarg)g(=)h(complex,)
330 872 y(testdb->)f(procedure)g(=)g(complex_cmp,)330
932 y(testdb->)g(commutator)g(=)g(=)330 992 y(testdb->)g();)330
1051 y(CREATE)330 1111 y(testdb=>)270 1211 y Ft(From)12
b(no)o(w)h(on)h(we)f(are)h(able)f(to)g(perform)f(comparisons)i(between)
f(comple)o(x)g(numbers)g(in)h(a)f(query')m(s)270 1271
y(quali02cation)f((W)l(e)g(use)h(the)f(table)g Fr(complex)p
1100 1271 15 2 v 17 w(test)g Ft(as)h(de02ned)f(in)h(e)o(xample)f
(2.8):)330 1371 y Fr(testdb=>)29 b(select)g(*)h(from)f(complex_test)
330 1431 y(testdb->)g(where)g(val)h(=)f('(1,2)';)390
1491 y(val)330 1550 y(-----)330 1610 y((1,2))330 1670
y((1)g(row))330 1789 y(testdb=>)g(select)g(*)h(from)f(complex_test)
330 1849 y(testdb->)g(where)g(val)h(=)f('(7,8)';)390
1909 y(val)330 1969 y(-----)330 2029 y((0)g(rows))330
2148 y(testdb=>)270 2291 y Fh(2.5.5)59 b(Extending)15
b(Aggr)o(egates)270 2385 y Ft(If)e(we)i(want)e(to)h(use)h(aggre)o(gate)
f(functions)f(on)h(attrib)o(utes)g(of)g(a)g(user)g(de02ned)g(type,)h
(we)g(ha)o(v)o(e)f(to)g(add)270 2445 y(aggre)o(gate)19
b(functions)f(designed)h(to)g(work)f(on)h(the)g(ne)o(w)f(type.)36
b(Aggre)o(gates)19 b(in)g(PostgreSQL)f(are)270 2504 y(realized)12
b(using)h(three)f(functions:)345 2604 y Fo(17)25 b
Fr(sfunc1)13 b Ft((state)i(function)e(one):)19 b(is)c(called)g(for)e
(e)o(v)o(ery)i(tuple)f(of)g(the)g(current)g(group)g(and)g(the)395
2664 y(appropriate)d(attrib)o(ute')m(s)h(v)o(alue)h(of)f(the)h(current)
f(tuple)g(is)h(passed)h(to)e(the)h(function.)j(The)d(gi)o(v)o(en)395
2724 y(ar)o(gument)f(is)h(used)h(to)e(change)i(the)f(internal)f(state)h
(of)g(the)g(function)f(in)h(the)g(way)f(gi)o(v)o(en)h(by)g(the)395
2784 y(body)f(of)h(the)g(function.)k(F)o(or)c(e)o(xample)g
Fr(sfunc1)g Ft(of)g(the)g(aggre)o(gate)f(function)h Fr(sum)g
Ft(is)g(called)395 2843 y(for)f(e)o(v)o(ery)h(tuple)g(of)g(the)h
(current)e(group.)19 b(The)14 b(v)o(alue)f(of)g(the)g(attrib)o(ute)g
(the)g(sum)h(is)g(b)o(uilt)e(on)i(is)395 2903 y(taken)d(from)h(the)g
(current)g(tuple)g(and)g(added)g(to)h(the)f(internal)g(sum)g(state)h
(of)f Fr(sfunc1)p Ft(.)345 3003 y Fo(17)25 b Fr(sfunc2)12
b Ft(is)h(also)g(called)g(for)g(e)o(v)o(ery)f(tuple)h(of)f(the)h(group)
g(b)o(ut)f(it)h(does)g(not)g(use)h(an)o(y)f(ar)o(gument)395
3063 y(from)g(outside)h(to)g(manipulate)g(its)h(state.)22
b(It)13 b(just)i(keeps)f(track)g(of)g(the)g(o)o(wn)g(internal)g(state.)
22 b(A)395 3123 y(typical)10 b(application)g(for)g Fr(sfunc2)h
Ft(is)g(a)g(counter)f(that)h(is)g(incremented)f(for)g(e)o(v)o(ery)h
(tuple)g(of)f(the)395 3183 y(group)h(that)h(has)h(been)g(processed.)345
3283 y Fo(17)25 b Fr(finalfunc)14 b Ft(is)i(called)f(after)g(all)g
(tuples)g(of)g(the)g(current)g(group)f(ha)o(v)o(e)i(been)f(processed.)
26 b(It)395 3342 y(takes)10 b(the)f(internal)h(state)g(of)g
Fr(sfunc1)f Ft(and)h(the)g(state)h(of)e Fr(sfunc2)h Ft(as)g(ar)o
(guments)g(and)g(deri)o(v)o(es)395 3402 y(the)h(result)h(of)f(the)h
(aggre)o(gate)g(function)f(from)f(the)i(two)f(gi)o(v)o(en)h(ar)o
(guments.)j(F)o(or)d(e)o(xample)f(with)p eop
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41 40 bop 198 60 a Fm(2.5.)29 b(SOME)12 b(OF)h(POSTGRESQL)-5
b('S)12 b(SPECIAL)h(FEA)-6 b(TURES)14 b(IN)e(DET)-5 b(AIL)340
b Ft(41)323 234 y(the)9 b(aggre)o(gate)h(function)f Fr(average)p
Ft(,)h Fr(sfunc1)f Ft(sums)h(up)g(the)f(attrib)o(ute)g(v)o(alues)h(of)f
(each)h(tuple)323 294 y(in)j(the)g(group,)g Fr(sfunc2)f
Ft(counts)i(the)f(tuples)g(in)g(the)g(group.)18 b Fr(finalfunc)12
b Ft(di)o(vides)h(the)g Fp(sum)323 354 y Ft(by)f(the)g
Fp(count)g Ft(to)g(deri)o(v)o(e)g(the)h(a)o(v)o(erage.)198
462 y(If)e(we)g(de02ne)g(an)g(aggre)o(gate)g(using)h(only)f
Fr(sfunc1)f Ft(we)i(get)f(an)g(aggre)o(gate)g(that)g(computes)h(a)f
(running)198 522 y(function)h(of)h(the)g(attrib)o(ute)f(v)o(alues)h
(from)f(each)i(tuple.)j Fr(sum)c Ft(is)h(an)f(e)o(xample)g(for)f(this)h
(kind)g(of)g(aggre-)198 582 y(gate.)18 b(On)13 b(the)g(other)g(hand,)h
(if)e(we)h(create)h(an)f(aggre)o(gate)g(function)f(using)h(only)g
Fr(sfunc2)g Ft(we)g(get)g(an)198 642 y(aggre)o(gate)i(that)g(is)g
(independent)g(of)g(the)g(attrib)o(ute)f(v)o(alues)h(from)g(each)g
(tuple.)24 b Fr(count)15 b Ft(is)g(a)g(typical)198 702
y(e)o(xample)d(of)g(this)h(kind)f(of)g(aggre)o(gate.)198
840 y Fn(Example)h(2.10)25 b Ft(Here)h(we)g(want)g(to)g(realize)g(the)g
(aggre)o(gate)g(functions)g Fr(complex)p 1796 840 15
2 v 17 w(sum)g Ft(and)198 899 y Fr(complex)p 411 899
V 17 w(avg)12 b Ft(for)g(the)g(user)h(de02ned)f(type)g
Fr(complex)g Ft((see)g(e)o(xample)h(2.8).)198 1019
y(First)53 b(we)h(ha)o(v)o(e)g(to)f(create)g(the)h(user)f(de02ned)h
(functions)f Fr(complex)p 1769 1019 V 17 w(add)g Ft(and)198
1079 y Fr(complex)p 411 1079 V 17 w(scalar)p 608 1079
V 17 w(div)p Ft(.)34 b(W)l(e)19 b(can)g(append)f(these)h(two)f
(functions)g(to)g(the)h(02le)f Fr(complex.c)198 1138
y Ft(from)11 b(e)o(xample)i(2.8)f(again)h((as)f(we)h(did)f(with)g
Fr(complex)p 1214 1138 V 17 w(cmp)p Ft():)258 1250 y
Fr(/*)29 b(Add)h(Complex)f(numbers)g(*/)258 1310 y(Complex)g(*)258
1370 y(complex_add(Complex)f(*arg1,)h(Complex)g(*arg2))258
1430 y({)318 1489 y(Complex)g(*result;)318 1609 y(result)g(=)h
((Complex)f(*)palloc(sizeof(Complex));)318 1669
y(result->x)f(=)i(arg1->x)f(+)h(arg2->x;)318 1729 y(result->y)e(=)i
(arg1->y)f(+)h(arg2->y;)318 1788 y(return(result);)258
1848 y(})258 1968 y(/*)f(Final)h(function)f(for)g(complex)g(average)h
(*/)258 2027 y(/*)f(Transform)g(arg1)h(to)f(polar)h(coordinate)f(form)
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%%Page: 46 46
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(ute.)p eop
%%Page: 47 47
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%%Page: 48 48
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%%Page: 49 49
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323 2200 y(for)c(correct)h(syntax)g(and)h(creates)f(a)h
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52 51 bop 270 60 a Ft(52)82 b Fm(CHAPTER)14 b(3.)28 b(POSTGRESQL)13
b(FR)n(OM)f(THE)i(PR)n(OGRAMMER'S)f(POINT)f(OF)g(VIEW)270
234 y Fi(3.2)71 b(Ho)o(w)18 b(Connections)f(ar)o(e)g(Established)270
370 y Ft(PostgreSQL)c(is)g(implemented)f(using)h(a)g(simple)g
(224process)h(per)o(-user224)e(client/serv)o(er)h(model.)k(In)c(this)
270 430 y(model)k(there)f(is)h(one)g Fp(client)g(pr)n(ocess)h
Ft(connected)f(to)f(e)o(xactly)i(one)e Fp(server)j(pr)n(ocess)p
Ft(.)30 b(As)18 b(we)f(don')o(t)270 490 y(kno)o(w)f Fp(per)h(se)g
Ft(ho)o(w)f(man)o(y)h(connections)g(will)f(be)g(made,)j(we)d(ha)o(v)o
(e)h(to)g(use)g(a)f Fp(master)i(pr)n(ocess)f Ft(that)270
549 y(spa)o(wns)h(a)e(ne)o(w)h Fp(server)h(pr)n(ocess)f
Ft(e)o(v)o(ery)f(time)h(a)f(connection)h(is)f(requested.)29
b(This)17 b Fp(master)g(pr)n(ocess)270 609 y Ft(is)f(called)g
Fr(postmaster)e Ft(and)i(listens)g(at)f(a)h(speci02ed)g(TCP/IP)f
(port)g(for)g(incoming)g(connections.)270 669 y(Whene)o(v)o(er)e(a)h
(request)f(for)f(a)i(connection)f(is)h(detected)f(the)g
Fr(postmaster)g Ft(process)g(spa)o(wns)i(a)e(ne)o(w)270
729 y Fp(server)i(pr)n(ocess)f Ft(called)g Fr(postgres)p
Ft(.)j(The)d(serv)o(er)g(tasks)g(()p Fr(postgres)e Ft(processes))i
(communicate)270 788 y(with)k(each)g(other)f(using)h
Fp(semaphor)n(es)h Ft(and)f Fp(shar)n(ed)h(memory)g Ft(to)e(ensure)h
(data)g(inte)o(grity)f(through-)270 848 y(out)j(concurrent)e(data)i
(access.)40 b(Figure)19 b(3.1)h(illustrates)f(the)h(interaction)f(of)g
(the)h(master)g(process)270 908 y Fr(postmaster)11 b
Ft(the)i(serv)o(er)f(process)h Fr(postgres)e Ft(and)i(a)f(client)h
(application.)345 981 y(The)e(client)g(process)g(can)h(either)e(be)h
(the)g Fr(psql)g Ft(frontend)f((for)f Fp(inter)o(active)j
Ft(SQL)f(queries))f(or)h(an)o(y)270 1041 y(user)f(application)f
(implemented)g(using)h(the)f Fr(libpg)h Ft(library)m(.)j(Note)d(that)f
(applications)h(implemented)270 1100 y(using)i Fr(ecpq)g
Ft((i.e.)k(the)d(postgres)f(embedded)g(C)h(compiler))e(also)i(use)g
(this)f(library)m(.)345 1173 y(Once)e(a)g(connection)f(is)i
(established)f(the)g(client)f(process)i(can)f(send)g(a)g(query)f(to)h
(the)g Fp(bac)o(kend)p Ft(.)15 b(The)270 1233 y(query)f(is)h
(transmitted)e(using)i Fp(plain)f(te)o(xt)p Ft(,)h(i.e.)23
b(there)14 b(is)h(no)f(parsing)g(done)h(in)f(the)h Fp(fr)n(ontend)f
Ft((client).)270 1293 y(The)i(serv)o(er)g Fp(parses)g
Ft(the)g(query)m(,)g(creates)g(an)g Fp(e)o(xecution)f(plan)p
Ft(,)i(e)o(x)o(ecutes)g(the)e Fp(plan)g Ft(and)h(returns)f(the)270
1352 y(retrie)o(v)o(ed)c(tuples)i(to)f(the)g(client)h(by)f
(transmitting)f(them)h(o)o(v)o(er)h(the)f(established)h(connection.)543
2309 y @beginspecial 180 @llx 310 @lly 431 @urx 482 @ury
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@endspecial 595 2973 a(Figure)11 b(3.3:)16 b Fp(Wher)n(eClause)e
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