db


SYNOPSIS
       #include <sys/types.h>
       #include <limits.h>
       #include <db.h>
       #include <fcntl.h>

       DB *dbopen(const char *file, int flags, int mode, DBTYPE type,
                  const void *openinfo);

DESCRIPTION
       Note  well:  This  page documents interfaces provided in glibc up until
       version 2.1.  Since version 2.2, glibc no longer provides these  inter-
       faces.   Probably,  you  are looking for the APIs provided by the libdb
       library instead.

       dbopen() is the library interface to  database  files.   The  supported
       file  formats are btree, hashed and UNIX file oriented.  The btree for-
       mat is a representation of a  sorted,  balanced  tree  structure.   The
       hashed  format is an extensible, dynamic hashing scheme.  The flat-file
       format is a byte stream file with fixed  or  variable  length  records.
       The  formats  and  file  format  specific  information are described in
       detail in their respective manual pages btree(3), hash(3) and recno(3).

       dbopen() opens file for reading and/or writing.  Files  never  intended
       to  be preserved on disk may be created by setting the file argument to
       NULL.

       The flags and mode arguments are as specified to the  open(2)  routine,
       however,  only  the  O_CREAT,  O_EXCL,  O_EXLOCK, O_NONBLOCK, O_RDONLY,
       O_RDWR, O_SHLOCK, and O_TRUNC flags are meaningful.  (Note,  opening  a
       database file O_WRONLY is not possible.)

       The  type  argument is of type DBTYPE (as defined in the <db.h> include
       file) and may be set to DB_BTREE, DB_HASH, or DB_RECNO.

       The openinfo argument is a pointer to an access method specific  struc-
       ture  described  in  the  access  method's manual page.  If openinfo is
       NULL, each access method will use defaults appropriate for  the  system
       and the access method.

       dbopen()  returns  a  pointer  to a DB structure on success and NULL on
       error.  The DB structure is defined in the  <db.h>  include  file,  and
       contains at least the following fields:

           typedef struct {
               DBTYPE type;
               int (*close)(const DB *db);
               int (*del)(const DB *db, const DBT *key, unsigned int flags);
               int (*fd)(const DB *db);
               int (*get)(const DB *db, DBT *key, DBT *data,
                          unsigned int flags);
               int (*put)(const DB *db, DBT *key, const DBT *data,
                          unsigned int flags);

       close  A pointer to a routine to flush any cached information to  disk,
              free  any allocated resources, and close the underlying file(s).
              Since key/data pairs may be cached in memory,  failing  to  sync
              the  file  with a close or sync function may result in inconsis-
              tent or lost information.  close routines  return  -1  on  error
              (setting errno) and 0 on success.

       del    A  pointer  to a routine to remove key/data pairs from the data-
              base.

              The argument flag may be set to the following value:

              R_CURSOR
                     Delete the record referenced by the cursor.   The  cursor
                     must have previously been initialized.

              delete  routines  return  -1 on error (setting errno), 0 on suc-
              cess, and 1 if the specified key was not in the file.

       fd     A pointer to a routine which returns a file descriptor represen-
              tative  of the underlying database.  A file descriptor referenc-
              ing the same file will be returned to all processes  which  call
              dbopen()  with  the same file name.  This file descriptor may be
              safely used as an argument to the fcntl(2) and flock(2)  locking
              functions.   The  file  descriptor is not necessarily associated
              with any of the underlying files used by the access method.   No
              file  descriptor  is available for in memory databases.  fd rou-
              tines return -1 on error (setting errno), and the file  descrip-
              tor on success.

       get    A  pointer  to  a  routine  which  is  the  interface  for keyed
              retrieval from the database.  The address and length of the data
              associated  with the specified key are returned in the structure
              referenced by data.  get routines return -1  on  error  (setting
              errno), 0 on success, and 1 if the key was not in the file.

       put    A pointer to a routine to store key/data pairs in the database.

              The argument flag may be set to one of the following values:

              R_CURSOR
                     Replace  the key/data pair referenced by the cursor.  The
                     cursor must have previously been initialized.

              R_IAFTER
                     Append the data immediately after the data referenced  by
                     key,  creating a new key/data pair.  The record number of
                     the appended key/data pair is returned in the key  struc-
                     ture.  (Applicable only to the DB_RECNO access method.)

              R_IBEFORE
                     Insert the data immediately before the data referenced by
                     key, creating a new key/data pair.  The record number  of
                     the  inserted key/data pair is returned in the key struc-

              access methods because it implies that the keys have an inherent
              order which does not change.

              R_IAFTER  and  R_IBEFORE  are  available  only  for the DB_RECNO
              access method because they each imply that the access method  is
              able  to  create  new  keys.   This is true only if the keys are
              ordered and independent, record numbers for example.

              The default behavior of the put routines is  to  enter  the  new
              key/data pair, replacing any previously existing key.

              put  routines  return -1 on error (setting errno), 0 on success,
              and 1 if the R_NOOVERWRITE flag was  set  and  the  key  already
              exists in the file.

       seq    A  pointer  to  a  routine which is the interface for sequential
              retrieval from the database.  The address and length of the  key
              are returned in the structure referenced by key, and the address
              and length of the data are returned in the structure  referenced
              by data.

              Sequential  key/data  pair  retrieval may begin at any time, and
              the position of the "cursor" is not affected  by  calls  to  the
              del,  get, put, or sync routines.  Modifications to the database
              during a sequential scan will be reflected in the scan, that is,
              records  inserted  behind  the cursor will not be returned while
              records inserted in front of the cursor will be returned.

              The flag value must be set to one of the following values:

              R_CURSOR
                     The data associated with the specified key  is  returned.
                     This  differs  from  the  get routines in that it sets or
                     initializes the cursor to the  location  of  the  key  as
                     well.    (Note,  for  the  DB_BTREE  access  method,  the
                     returned key is not necessarily an exact  match  for  the
                     specified  key.   The  returned  key  is the smallest key
                     greater than or equal to the  specified  key,  permitting
                     partial key matches and range searches.)

              R_FIRST
                     The  first key/data pair of the database is returned, and
                     the cursor is set or initialized to reference it.

              R_LAST The last key/data pair of the database is  returned,  and
                     the  cursor  is  set  or  initialized  to  reference  it.
                     (Applicable only to  the  DB_BTREE  and  DB_RECNO  access
                     methods.)

              R_NEXT Retrieve  the key/data pair immediately after the cursor.
                     If the cursor is not yet set, this is  the  same  as  the
                     R_FIRST flag.

              R_PREV Retrieve the key/data pair immediately before the cursor.
              and no complete key/data pairs are currently available, the  seq
              routines return 2.

       sync   A  pointer to a routine to flush any cached information to disk.
              If the database is in memory  only,  the  sync  routine  has  no
              effect and will always succeed.

              The flag value may be set to the following value:

              R_RECNOSYNC
                     If  the  DB_RECNO  access method is being used, this flag
                     causes the sync routine to apply to the btree file  which
                     underlies  the  recno  file,  not  the recno file itself.
                     (See the bfname field of the  recno(3)  manual  page  for
                     more information.)

              sync  routines  return -1 on error (setting errno) and 0 on suc-
              cess.

   Key/data pairs
       Access to all file types is based on key/data  pairs.   Both  keys  and
       data are represented by the following data structure:

           typedef struct {
               void  *data;
               size_t size;
           } DBT;

       The elements of the DBT structure are defined as follows:

       data   A pointer to a byte string.

       size   The length of the byte string.

       Key  and  data byte strings may reference strings of essentially unlim-
       ited length although any two of them must fit into available memory  at
       the  same  time.  It should be noted that the access methods provide no
       guarantees about byte string alignment.

ERRORS
       The dbopen() routine may fail and set errno for any of the errors spec-
       ified for the library routines open(2) and malloc(3) or the following:

       EFTYPE A file is incorrectly formatted.

       EINVAL A  parameter  has been specified (hash function, pad byte, etc.)
              that is incompatible with  the  current  file  specification  or
              which  is  not  meaningful for the function (for example, use of
              the cursor without prior initialization) or there is a  mismatch
              between the version number of file and the software.

       The  close routines may fail and set errno for any of the errors speci-
       fied for the library routines close(2), read(2), write(2), free(3),  or
       fsync(2).
       The  typedef  DBT  is  a  mnemonic  for "data base thang", and was used
       because no-one could think of a reasonable  name  that  wasn't  already
       used.

       The  file  descriptor  interface  is  a kludge and will be deleted in a
       future version of the interface.

       None of the access methods provide any form of concurrent access, lock-
       ing, or transactions.

SEE ALSO
       btree(3), hash(3), mpool(3), recno(3)

       LIBTP:  Portable, Modular Transactions for UNIX, Margo Seltzer, Michael
       Olson, USENIX proceedings, Winter 1992.

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



4.4 Berkeley Distribution         2012-05-04                         DBOPEN(3)
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