hash.3.ps

早期freebsd实现

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/F0 10/Times-Roman@0 SF 136.79(HASH\(3\) BSD)72 48 R(Programmer')2.5 E 2.5(sM)
-.55 G 136.79(anual HASH\(3\))340.17 48 R/F1 9/Times-Bold@0 SF -.18(NA)72 84 S
(ME).18 E F0(hash \255 hash database access method)108 96 Q F1(SYNOPSIS)72
112.8 Q/F2 10/Times-Bold@0 SF(#include <sys/types.h>)108 124.8 Q(#include <db)
108 136.8 Q(.h>)-.4 E F1(DESCRIPTION)72 153.6 Q F0 .29(The routine)108 165.6 R
/F3 10/Times-Italic@0 SF(dbopen)2.79 E F0 .29(is the library interf)2.79 F .29
(ace to database \214les.)-.1 F .29
(One of the supported \214le formats is hash \214les.)5.29 F .974
(The general description of the database access methods is in)108 177.6 R F3
(dbopen)3.475 E F0 .975(\(3\), this manual page describes only).24 F
(the hash speci\214c information.)108 189.6 Q(The hash data structure is an e)
108 206.4 Q(xtensible, dynamic hashing scheme.)-.15 E .83
(The access method speci\214c data structure pro)108 223.2 R .83(vided to)-.15
F F3(dbopen)3.33 E F0 .83(is de\214ned in the <db)3.33 F .83
(.h> include \214le as fol-)-.4 F(lo)108 235.2 Q(ws:)-.25 E(typedef struct {)
108 259.2 Q(int bsize;)144 271.2 Q(int cachesize;)144 283.2 Q(int f)144 295.2 Q
-.1(fa)-.25 G(ctor;).1 E(u_long \(*hash\)\(const v)144 307.2 Q
(oid *, size_t\);)-.2 E(int lorder;)144 319.2 Q(int nelem;)144 331.2 Q 2.5(}H)
108 343.2 S(ASHINFO;)122.52 343.2 Q
(The elements of this structure are as follo)108 360 Q(ws:)-.25 E(bsize)108
376.8 Q F3(Bsize)144 376.8 Q F0 1.393(de\214nes the hash table b)3.893 F(uck)
-.2 E 1.393(et size, and is, by def)-.1 F 1.394(ault, 256 bytes.)-.1 F 1.394
(It may be preferable to)6.394 F
(increase the page size for disk-resident tables and tables with lar)144 388.8
Q(ge data items.)-.18 E(cachesize)108 405.6 Q 3.16(As)144 417.6 S .66
(uggested maximum size, in bytes, of the memory cache.)158.27 417.6 R .659
(This v)5.659 F .659(alue is)-.25 F F2(only)3.159 E F0(advisory)3.159 E 3.159
(,a)-.65 G .659(nd the)514.621 417.6 R
(access method will allocate more memory rather than f)144 429.6 Q(ail.)-.1 E
-2.1 -.25(ff a)108 446.4 T(ctor).25 E F3(Ffactor)9.7 E F0 .482
(indicates a desired density within the hash table.)2.981 F .482
(It is an approximation of the number of)5.482 F -.1(ke)144 458.4 S .429
(ys allo)-.05 F .429(wed to accumulate in an)-.25 F 2.929(yo)-.15 G .429(ne b)
291.454 458.4 R(uck)-.2 E .429(et, determining when the hash table gro)-.1 F
.428(ws or shrinks.)-.25 F(The def)144 470.4 Q(ault v)-.1 E(alue is 8.)-.25 E
(hash)108 487.2 Q F3(Hash)144 487.2 Q F0 .1(is a user de\214ned hash function.)
2.6 F .1(Since no hash function performs equally well on all possible)5.1 F
.924(data, the user may \214nd that the b)144 499.2 R .923
(uilt-in hash function does poorly on a particular data set.)-.2 F(User)5.923 E
1.408(speci\214ed hash functions must tak)144 511.2 R 3.909(et)-.1 G 1.609 -.1
(wo a)293.431 511.2 T -.18(rg).1 G 1.409
(uments \(a pointer to a byte string and a length\) and).18 F
(return an u_long to be used as the hash v)144 523.2 Q(alue.)-.25 E 9.62
(lorder The)108 540 R 1.597(byte order for inte)4.097 F 1.596
(gers in the stored database metadata.)-.15 F 1.596
(The number should represent the)6.596 F .688(order as an inte)144 552 R .689
(ger; for e)-.15 F .689(xample, big endian order w)-.15 F .689
(ould be the number 4,321.)-.1 F(If)5.689 E F3(lor)3.189 E(der)-.37 E F0 .689
(is 0 \(no)3.189 F .822(order is speci\214ed\) the current host order is used.)
144 564 R .822(If the)5.822 F .822(\214le already e)5.822 F .821
(xists, the speci\214ed v)-.15 F .821(alue is)-.25 F(ignored and the v)144 576
Q(alue speci\214ed when the tree w)-.25 E(as created is used.)-.1 E(nelem)108
592.8 Q F3(Nelem)144 592.8 Q F0 .701
(is an estimate of the \214nal size of the hash table.)3.2 F .701
(If not set or set too lo)5.701 F 2.001 -.65(w, h)-.25 H .701(ash tables will)
.65 F -.15(ex)144 604.8 S .448(pand gracefully as k).15 F -.15(ey)-.1 G 2.948
(sa).15 G .448(re entered, although a slight performance de)255.912 604.8 R
.447(gradation may be noticed.)-.15 F(The def)144 616.8 Q(ault v)-.1 E
(alue is 1.)-.25 E .79(If the \214le already e)108 633.6 R .79
(xists \(and the O_TR)-.15 F .79(UNC \215ag is not speci\214ed\), the v)-.4 F
.79(alues speci\214ed for the parameters)-.25 F(bsize, f)108 645.6 Q -.1(fa)
-.25 G(ctor).1 E 2.5(,l)-.4 G(order and nelem are ignored and the v)167.23
645.6 Q(alues speci\214ed when the tree w)-.25 E(as created are used.)-.1 E
1.232(If a hash function is speci\214ed,)108 662.4 R F3(hash_open)3.731 E F0
1.231(will attempt to determine if the hash function speci\214ed is the)3.731 F
(same as the one with which the database w)108 674.4 Q(as created, and will f)
-.1 E(ail if it is not.)-.1 E(Backw)108 691.2 Q .861(ard compatible interf)-.1
F .861(aces to the routines described in)-.1 F F3(dbm)3.362 E F0 .862
(\(3\), and).32 F F3(ndbm)3.362 E F0 .862(\(3\) are pro).32 F .862(vided, ho)
-.15 F(we)-.25 E -.15(ve)-.25 G -.4(r,).15 G(4.4 Berk)72 732 Q(ele)-.1 E 2.5
(yD)-.15 G(istrib)132.57 732 Q 96.815(ution August)-.2 F(17, 1993)2.5 E(1)535
732 Q EP
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(arson, Communications of the A)242.86 136.8 Q(CM, April 1988.)-.4 E F2 2.5(AN)
108 160.8 S .3 -.15(ew H)123.28 160.8 T(ash P).15 E(ac)-.8 E(ka)-.2 E .2 -.1
(ge f)-.1 H(or UNIX).1 E F0 2.5(,M).94 G(ar)248.41 160.8 Q(go Seltzer)-.18 E
2.5(,U)-.4 G(SENIX Proceedings, W)308.09 160.8 Q(inter 1991.)-.4 E F1 -.09(BU)
72 177.6 S(GS).09 E F0(Only big and little endian byte order is supported.)108
189.6 Q(4.4 Berk)72 732 Q(ele)-.1 E 2.5(yD)-.15 G(istrib)132.57 732 Q 96.815
(ution August)-.2 F(17, 1993)2.5 E(2)535 732 Q EP
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