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diff --git a/src/util/db2/man/db_hash.3 b/src/util/db2/man/db_hash.3 new file mode 100644 index 0000000..adb88fc --- /dev/null +++ b/src/util/db2/man/db_hash.3 @@ -0,0 +1,138 @@ +.\" Copyright (c) 1990, 1993, 1994, 1995 +.\" 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. +.\" +.\" @(#)db_hash.3 8.13 (Berkeley) 8/1/95 +.\" +.TH DB_HASH 3 "August 1, 1995" +.UC 7 +.SH NAME +db_hash \- hash database access method +.SH DESCRIPTION +.so db.so +.GN +specific details of the hashing access method. +.PP +The hash data structure is an extensible, dynamic hashing scheme. +Backward compatible interfaces to the functions described in +.IR dbm (3), +and +.IR ndbm (3) +are provided, however these interfaces are not compatible with +previous file formats. +.SH "ACCESS METHOD SPECIFIC INFORMATION" +The hash access method specific data structure provided to +.I db_open +is typedef'd and named HASHINFO. +A HASHINFO structure has at least the following fields, +which may be initialized before calling +.IR db_open : +.TP 5 +u_int bsize; +.I Bsize +defines the hash table bucket size, and is, by default, 256 bytes. +It may be preferable to increase the page size for disk-resident tables +and tables with large data items. +.TP 5 +u_int cachesize; +A suggested maximum size, in bytes, of the memory cache. +This value is +.B only +advisory, and the access method will allocate more memory rather +than fail. +.TP 5 +u_int ffactor; +.I Ffactor +indicates a desired density within the hash table. +It is an approximation of the number of keys allowed to accumulate in any +one bucket, determining when the hash table grows or shrinks. +The default value is 8. +.TP 5 +u_int32_t (*hash)(const void *, size_t); +.I Hash +is a user defined hash function. +Since no hash function performs equally well on all possible data, the +user may find that the built-in hash function does poorly on a particular +data set. +User specified hash functions must take two arguments (a pointer to a byte +string and a length) and return a 32-bit quantity to be used as the hash +value. +.IP +If a hash function is specified, +.I hash_open +will attempt to determine if the hash function specified is the same as +the one with which the database was created, and will fail if it is not. +.TP 5 +int 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 +.I lorder +is 0 (no order is specified) the current host order is used. +If the file already exists, the specified value is ignored and the +value specified when the tree was created is used. +.TP 5 +u_int nelem; +.I Nelem +is an estimate of the final size of the hash table. +If not set or set too low, hash tables will expand gracefully as keys +are entered, although a slight performance degradation may be noticed. +The default value is 1. +.PP +If the file already exists (and the O_TRUNC flag is not specified), the +values specified for the parameters bsize, ffactor, lorder and nelem are +ignored and the values specified when the tree was created are used. +.SH "DB OPERATIONS" +The functions returned by +.I db_open +for the hash access method are as described in +.IR db_open (3). +.SH ERRORS +The +.I hash +access method functions may fail and set +.I errno +for any of the errors specified for the library function +.IR db_open (3). +.SH "SEE ALSO" +.IR db_btree (3), +.IR db_lock (3), +.IR db_log (3), +.IR db_mpool (3), +.IR db_open (3), +.IR db_recno (3), +.IR db_txn (3) +.sp +.IR "Dynamic Hash Tables" , +Per-Ake Larson, Communications of the ACM, April 1988. +.sp +.IR "A New Hash Package for UNIX" , +Margo Seltzer, USENIX Proceedings, Winter 1991. |