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diff --git a/lib/libc/db/man/btree.3 b/lib/libc/db/man/btree.3 new file mode 100644 index 0000000..99b2b15 --- /dev/null +++ b/lib/libc/db/man/btree.3 @@ -0,0 +1,272 @@ +.\" Copyright (c) 1990, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)btree.3 8.4 (Berkeley) 8/18/94 +.\" $FreeBSD$ +.\" +.Dd August 18, 1994 +.Dt BTREE 3 +.Os +.Sh NAME +.Nm btree +.Nd "btree database access method" +.Sh SYNOPSIS +.In sys/types.h +.In db.h +.Sh DESCRIPTION +The routine +.Fn dbopen +is the library interface to database files. +One of the supported file formats is +.Nm +files. +The general description of the database access methods is in +.Xr dbopen 3 , +this manual page describes only the +.Nm +specific information. +.Pp +The +.Nm +data structure is a sorted, balanced tree structure storing +associated key/data pairs. +.Pp +The +.Nm +access method specific data structure provided to +.Fn dbopen +is defined in the +.Aq Pa db.h +include file as follows: +.Bd -literal +typedef struct { + u_long flags; + u_int cachesize; + int maxkeypage; + int minkeypage; + u_int psize; + int (*compare)(const DBT *key1, const DBT *key2); + size_t (*prefix)(const DBT *key1, const DBT *key2); + int lorder; +} BTREEINFO; +.Ed +.Pp +The elements of this structure are as follows: +.Bl -tag -width indent +.It Va flags +The flag value is specified by +.Em or Ns 'ing +any of the following values: +.Bl -tag -width indent +.It Dv R_DUP +Permit duplicate keys in the tree, i.e. permit insertion if the key to be +inserted already exists in the tree. +The default behavior, as described in +.Xr dbopen 3 , +is to overwrite a matching key when inserting a new key or to fail if +the +.Dv R_NOOVERWRITE +flag is specified. +The +.Dv R_DUP +flag is overridden by the +.Dv R_NOOVERWRITE +flag, and if the +.Dv R_NOOVERWRITE +flag is specified, attempts to insert duplicate keys into +the tree will fail. +.Pp +If the database contains duplicate keys, the order of retrieval of +key/data pairs is undefined if the +.Va get +routine is used, however, +.Va seq +routine calls with the +.Dv R_CURSOR +flag set will always return the logical +.Dq first +of any group of duplicate keys. +.El +.It Va cachesize +A suggested maximum size (in bytes) of the memory cache. +This value is +.Em only +advisory, and the access method will allocate more memory rather than fail. +Since every search examines the root page of the tree, caching the most +recently used pages substantially improves access time. +In addition, physical writes are delayed as long as possible, so a moderate +cache can reduce the number of I/O operations significantly. +Obviously, using a cache increases (but only increases) the likelihood of +corruption or lost data if the system crashes while a tree is being modified. +If +.Va cachesize +is 0 (no size is specified) a default cache is used. +.It Va maxkeypage +The maximum number of keys which will be stored on any single page. +Not currently implemented. +.\" The maximum number of keys which will be stored on any single page. +.\" Because of the way the +.\" .Nm +.\" data structure works, +.\" .Va maxkeypage +.\" must always be greater than or equal to 2. +.\" If +.\" .Va maxkeypage +.\" is 0 (no maximum number of keys is specified) the page fill factor is +.\" made as large as possible (which is almost invariably what is wanted). +.It Va minkeypage +The minimum number of keys which will be stored on any single page. +This value is used to determine which keys will be stored on overflow +pages, i.e. if a key or data item is longer than the pagesize divided +by the minkeypage value, it will be stored on overflow pages instead +of in the page itself. +If +.Va minkeypage +is 0 (no minimum number of keys is specified) a value of 2 is used. +.It Va psize +Page size is the size (in bytes) of the pages used for nodes in the tree. +The minimum page size is 512 bytes and the maximum page size is 64K. +If +.Va psize +is 0 (no page size is specified) a page size is chosen based on the +underlying file system I/O block size. +.It Va compare +Compare is the key comparison function. +It must return an integer less than, equal to, or greater than zero if the +first key argument is considered to be respectively less than, equal to, +or greater than the second key argument. +The same comparison function must be used on a given tree every time it +is opened. +If +.Va compare +is +.Dv NULL +(no comparison function is specified), the keys are compared +lexically, with shorter keys considered less than longer keys. +.It Va prefix +.Va Prefix +is the prefix comparison function. +If specified, this routine must return the number of bytes of the second key +argument which are necessary to determine that it is greater than the first +key argument. +If the keys are equal, the key length should be returned. +Note, the usefulness of this routine is very data dependent, but, in some +data sets can produce significantly reduced tree sizes and search times. +If +.Va prefix +is +.Dv NULL +(no prefix function is specified), +.Em and +no comparison function is specified, a default lexical comparison routine +is used. +If +.Va prefix +is +.Dv NULL +and a comparison routine is specified, no prefix comparison is +done. +.It Va lorder +The byte order for integers in the stored database metadata. +The number should represent the order as an integer; for example, +big endian order would be the number 4,321. +If +.Va lorder +is 0 (no order is specified) the current host order is used. +.El +.Pp +If the file already exists (and the +.Dv O_TRUNC +flag is not specified), the +values specified for the parameters +.Va flags , lorder +and +.Va psize +are ignored +in favor of the values used when the tree was created. +.Pp +Forward sequential scans of a tree are from the least key to the greatest. +.Pp +Space freed up by deleting key/data pairs from the tree is never reclaimed, +although it is normally made available for reuse. +This means that the +.Nm +storage structure is grow-only. +The only solutions are to avoid excessive deletions, or to create a fresh +tree periodically from a scan of an existing one. +.Pp +Searches, insertions, and deletions in a +.Nm +will all complete in +O lg base N where base is the average fill factor. +Often, inserting ordered data into +.Nm Ns s +results in a low fill factor. +This implementation has been modified to make ordered insertion the best +case, resulting in a much better than normal page fill factor. +.Sh ERRORS +The +.Nm +access method routines may fail and set +.Va errno +for any of the errors specified for the library routine +.Xr dbopen 3 . +.Sh SEE ALSO +.Xr dbopen 3 , +.Xr hash 3 , +.Xr mpool 3 , +.Xr recno 3 +.Rs +.%T "The Ubiquitous B-tree" +.%A Douglas Comer +.%J "ACM Comput. Surv. 11" +.%N 2 +.%D June 1979 +.%P 121-138 +.Re +.Rs +.%A Bayer +.%A Unterauer +.%T "Prefix B-trees" +.%J "ACM Transactions on Database Systems" +.%N 1 +.%V Vol. 2 +.%D March 1977 +.%P 11-26 +.Re +.Rs +.%B "The Art of Computer Programming Vol. 3: Sorting and Searching" +.%A D. E. Knuth +.%D 1968 +.%P 471-480 +.Re +.Sh BUGS +Only big and little endian byte order is supported. |
