path: root/doc/gdbm.3

.\" This file is part of GDBM.
.\" Copyright (C) 2011, 2013 Free Software Foundation, Inc.
.\"
.\" GDBM is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 3, or (at your option)
.\" any later version.
.\"
.\" GDBM is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public License
.\" along with GDBM. If not, see <http://www.gnu.org/licenses/>. */
.TH GDBM 3 "May 8, 2013" "GDBM" "GDBM User Reference"
.SH NAME
GDBM \- The GNU database manager.  Includes \fBdbm\fR and \fBndbm\fR
compatibility.
.SH SYNOPSIS
.nf
.B #include <gdbm.h>
.sp
.BI "extern gdbm_error"  " gdbm_errno";
.br
.BI "extern char *" gdbm_version ;
.br
.BI "GDBM_FILE gdbm_open (const char *" name ", int " block_size ", "
.ti +21
.BI     "int " flags ", int " mode ", "
.ti +21
.BI "void (*" fatal_func ")(const char *))";
.br
.BI "void gdbm_close (GDBM_FILE " dbf ");"
.br
.BI "int gdbm_store (GDBM_FILE " dbf ", datum " key ", datum " content ", int " flag );
.br
.BI "datum gdbm_fetch (GDBM_FILE " dbf ", datum " key );
.br
.BI "int gdbm_delete (GDBM_FILE " dbf ", datum " key );
.br
.BI "datum gdbm_firstkey (GDBM_FILE " dbf ");"
.br
.BI "datum gdbm_nextkey (GDBM_FILE " dbf ", datum " key );
.br
.BI "int gdbm_reorganize (GDBM_FILE " dbf ");"
.br
.BI "void gdbm_sync (GDBM_FILE " dbf ");"
.br
.BI "int gdbm_exists (GDBM_FILE " dbf ", datum " key );
.br
.BI "const char *gdbm_strerror (gdbm_error " errno );
.br
.BI "int gdbm_setopt (GDBM_FILE " dbf ", int " option ", int " value ", int " size );
.br
.BI "int gdbm_fdesc (GDBM_FILE " dbf );
.br
.PP
.SS DBM Compatability routines:
.PP
.B #include <dbm.h>
.sp
.BI "int dbminit (const char *" name ");"
.br
.BI "int store (datum " key ", datum " content );
.br
.BI "datum fetch (datum " key );
.br
.BI "int delete (datum " key );
.br
.BI "datum firstkey (void);"
.br
.BI "datum nextkey (datum " key );
.br
.BI "int dbmclose (void);"
.PP
.SS NDBM Compatability routines:
.PP
.B #include <ndbm.h>
.sp
.BI "DBM *dbm_open (const char *" name ", int " flags ", int " mode );
.br
.BI "void dbm_close (DBM *" file );
.BI datum dbm_fetch (DBM *" file ", datum " key );
.br
.BI "int dbm_store (DBM *" file ", datum " key ", datum " content ", int " flags );
.br
.BI "int dbm_delete (DBM *" file ", datum " key );
.br
.BI "datum dbm_firstkey (DBM *" file );
.br
.BI "datum dbm_nextkey (DBM *" file ", datum " key );
.br
.BI "int dbm_error (DBM *" file );
.br
.BI "int dbm_clearerr (DBM *" file );
.br
.BI "int dbm_pagfno (DBM *" file );
.br
.BI "int dbm_dirfno (DBM *" file );
.br
.BI "int dbm_rdonly (DBM *" file );
.SH DESCRIPTION
\fBGNU dbm\fR is a library of routines that manages data files that contain
key/data pairs.  The access provided is that of storing, 
retrieval, and deletion by key and a non-sorted traversal of all
keys.  A process is allowed to use multiple data files at the
same time.

This manpage is a short description of the \fBGDBM\fR library.
For a detailed discussion, including examples of the configuration and
usage recommendations, refer to the \fBGDBM Manual\fR available in
Texinfo format.  To access it, run:

  \fBinfo gdbm\fR

Should any discrepancies occur between this manpage and the
\fBGDBM Manual\fR, the later shall be considered the authoritative
source.

A process that opens a gdbm file is designated as a "reader" or a
"writer".  Only one writer may open a gdbm file and many readers may
open the file.  Readers and writers can not open the gdbm file at the
same time. The procedure for opening a gdbm file is:

.BI "GDBM_FILE gdbm_open (const char *" name ", int " block_size ", "
.ti +21
.BI     "int " flags ", int " mode ", "
.ti +21
.BI "void (*" fatal_func ")(const char *))";

\fIName\fR is the name of the file (the complete name,
gdbm does not append any characters to this name).  \fIBlock_size\fR is
the size of a single transfer from disk to memory. This parameter is
ignored unless the file is a new file.  The minimum size is 512.  If
it is less than 512, dbm will use the stat block size for the file system.
\fIRead_write\fR can have one of the following values:
.TP
.B GDBM_READER
reader
.TP
.B GDBM_WRITER
writer
.TP
.B GDBM_WRCREAT
writer - if database does not exist create new one
.TP
.B GDBM_NEWDB
writer - create new database regardless if one exists
.PP
The \fBGDBM_NOMMAP\fR added to \fIread_write\fR by bitwise or instructs
\fBgdbm_open\fR to disable the use of
.BR mmap (2).
.PP
For the last three (writers of the database) the following may be added
added to \fIread_write\fR by bitwise or:
.TP
.B GDBM_SYNC
Causes all database operations to be synchronized to the disk,
.TP
.B GDBM_NOLOCK
Pevents the library from performing any locking on the database file.
.PP
The option
.B GDBM_FAST
is now obsolete, since gdbm defaults to no-sync mode.
.PP
\fIMode\fR is the file mode (see \fBchmod(2)\fR and \fBopen(2)\fR) if the
file is created. \fI(*Fatal_func) ()\fR is a function for dbm to call
if it detects a fatal error. The only parameter of this function is a string.
If the value of 0 is provided, \fBgdbm\fR will use a default function.

The return value is the pointer needed by all other routines to
access that gdbm file.  If the return is the NULL pointer, \fBgdbm_open\fR
was not successful.  The errors can be found in \fIgdbm_errno\fR for gdbm
errors and in \fIerrno\fR for system errors.  (For error codes, see
gdbmerrno.h.)

In all of the following calls, the parameter \fIdbf\fR refers to the pointer
returned from \fBgdbm_open\fR.

It is important that every file opened is also closed.  This is needed to
update the reader/writer count on the file.  This is done by:

.BI "void gdbm_close (GDBM_FILE " dbf ");"

The database is used by 3 primary routines.  The first stores data in the
database.

.BI "int gdbm_store (GDBM_FILE " dbf ", datum " key ", datum " content ", int " flag );

\fIDbf\fR is the pointer returned by \fBgdbm_open\fR.  \fIKey\fR is the
key data.  \fIContent\fR is the data to be associated with the \fIkey\fR.
\fIFlag\fR can have one of the following values:
.TP
.B GDBM_INSERT
Insert only, generate an error if key exists;
.TP
.B GDBM_REPLACE
Replace contents if key exists.
.PP
If a reader calls \fBgdbm_store\fR, the return value will be  \-1.
If called with \fBGDBM_INSERT\fR and \fIkey\fR is in the database, the return
value will be 1.  Otherwise, the return value is 0.

\fINOTICE: If you store data for a key that is already in the data base,
\fBgdbm\fI replaces the old data with the new data if called with \fBGDBM_REPLACE\fI.
You do not get two data items for the same key and you do not get an
error from \fBgdbm_store\fI.

NOTICE: The size in \fBgdbm\fI is not restricted like in \fBdbm\fI or \fBndbm\fI.  Your data
can be as large as you want.\fR

To search for some data, use:

.BI "datum gdbm_fetch (GDBM_FILE " dbf ", datum " key );

\fIDbf\fR is the pointer returned by \fBgdbm_open\fR.  \fIKey\fR is
the key data.

If the \fIdptr\fR element of the return value is NULL, no data was
found.  Otherwise the return value is a pointer to the found data.
The storage space for the \fIdptr\fR element is allocated using
\fBmalloc(3)\fR.  \fBGdbm\fI does not automatically free this data.
It is the programmer's responsibility to free this storage when it is
no longer needed.

To search for some data, without retrieving it:

.BI "int gdbm_exists (GDBM_FILE " dbf ", datum " key );

\fIDbf\fR is the pointer returned by \fBgdbm_open\fR.  \fIKey\fR is
the key data to search for.

If the \fIkey\fR is found within the database, the return value 
will be true.  If nothing appropiate is found, false is returned.
This routine is useful for checking for the existence of a record,
without performing the memory allocation done by \fBgdbm_fetch\fR.
.PP
To remove some data from the database:

.BI "int gdbm_delete (GDBM_FILE " dbf ", datum " key );

\fIDbf\fR is the pointer returned by \fBgdbm_open\fR.  \fIKey\fR is the
key data.

The return value is \-1 if the item is not present or the requester is a reader.
The return value is 0 if there was a successful delete.

The next two routines allow for accessing all items in the database.  This 
access is not key sequential, but it is guaranteed to visit every key in
the database once.  (The order has to do with the hash values.)

.BI "datum gdbm_firstkey (GDBM_FILE " dbf ");"
.br
.BI "datum gdbm_nextkey (GDBM_FILE " dbf ", datum " key );

\fIDbf\fR is the pointer returned by \fBgdbm_open\fR. \fIKey\fR is the
key data.

The return values are both of type \fBdatum\fR.  If the \fIdptr\fR
element of the return value is NULL, there is no first key or next key.
Again notice that \fIdptr\fR points to data allocated by \fBmalloc(3)\fR
and \fBgdbm\fR will not free it for you. 

These functions were intended to visit the database in read-only algorithms,
for instance, to validate the database or similar operations.

File `visiting' is based on a `hash table'.  \fIgdbm_delete\fR re-arranges the
hash table to make sure that any collisions in the table do not leave some item
`un-findable'.  The original key order is NOT guaranteed to remain unchanged in
ALL instances.  It is possible that some key will not be visited if a loop like
the following is executed:
.sp
.nf
.in +5
key = gdbm_firstkey (dbf);
while (key.dptr)
  {
    nextkey = gdbm_nextkey (dbf, key);
    if (some condition)
      gdbm_delete ( dbf, key );
    free (key.dptr);
    key = nextkey;
  }
.in
.fi
.PP
The following routine should be used very infrequently.
  
.BI "int gdbm_reorganize (GDBM_FILE " dbf ");"

If you have had a lot of deletions and would like to shrink the space
used by the \fBgdbm\fR file, this routine will reorganize the database.
\fBGdbm\fR will not shorten the length of a \fBgdbm\fR file except by
using this reorganization.  (Deleted file space will be reused.)

Unless your database was opened with the \fBGDBM_SYNC\fR flag, \fBgdbm\fR does not
wait for writes to be flushed to the disk before continuing.
The following routine can be used to guarantee that the database is
physically written to the disk file.

.BI "void gdbm_sync (GDBM_FILE " dbf ");"

It will not return until the disk file state is syncronized with the
in-memory state of the database.

To convert a \fBgdbm\fR error code into English text, use this routine:

.BI "const char *gdbm_strerror (gdbm_error " errno );

\fBGdbm\fR now supports the ability to set certain options on an
already open database.

.BI "int gdbm_setopt (GDBM_FILE " dbf ", int " option ", int " value ", int " size );

Where \fIdbf\fR is the return value from a previous call to \fBgdbm_open\fR,
and \fIoption\fR specifies which option to set.  The valid options are
currently:
.TP
.B GDBM_CACHESIZE
Set the size of the internal bucket cache. This option may only be set once
on each \fIGDBM_FILE\fR descriptor, and is set automatically to 100 upon the
first access to the database.
.TP
.B GDBM_FASTMODE
 Set \fBfast mode\fR to either on or off.  This allows \fBfast mode\fR to
be toggled on an already open and active database. \fIvalue\fR (see below)
should be set to either TRUE or FALSE.  \fIThis option is now obsolete.\fR
.TP
.B GDBM_SYNCMODE
Turn on or off file system synchronization operations.  This setting defaults
to off; \fIvalue\fR (see below) should be set to either TRUE or FALSE.
.TP
.B GDBM_CENTFREE
Set \fBcentral free block pool\fR to either on or off.
The default is off, which is how previous versions of \fBGdbm\fR
handled free blocks. If set, this option causes all subsequent free
blocks to be placed in the \fBglobal\fR pool, allowing (in thoery)
more file space to be reused more quickly. \fIvalue\fR (see below) should
be set to either TRUE or FALSE.
\fINOTICE: This feature is still under study.\fR
.TP
.B GDBM_COALESCEBLKS
Set \fBfree block merging\fR to either on or off.
The default is off, which is how previous versions of \fBGdbm\fR
handled free blocks. If set, this option causes adjacent free blocks
to be merged.  This can become a CPU expensive process with time, though,
especially if used in conjunction with \fBGDBM_CENTFREE\fR. \fIvalue\fR
(see below) should be set to either TRUE or FALSE.
\fINOTICE: This feature is still under study.\fR
.PP
\fIvalue\fR is the value to set \fIoption\fR to, specified as an integer
pointer.  \fIsize\fR is the size of the data pointed to by \fIvalue\fR.
The return value will be \-1 upon failure, or 0 upon success.  The global
variable \fIgdbm_errno\fR will be set upon failure.

For instance, to set a database to use a cache of 10, after opening it
with \fBgdbm_open\fR, but prior to accessing it in any way, the following
code could be used:
.sp
.nf
.in +5
int value = 10;
  
ret = gdbm_setopt( dbf, GDBM_CACHESIZE, &value, sizeof(int));
.in
.fi
.PP
If the database was opened with the \fBGDBM_NOLOCK\fR flag, the user may
wish to perform their own file locking on the database file in order to
prevent multiple writers operating on the same file simultaneously.

In order to support this, the \fIgdbm_fdesc\fR routine is provided.

.BI "int gdbm_fdesc (GDBM_FILE " dbf );

Where \fIdbf\fR is the return value from a previous call to \fBgdbm_open\fR.
The return value will be the file descriptor of the database.

The following two external variables may be useful:

\fIgdbm_errno\fR is the variable that contains more information about
gdbm errors.  (gdbm.h has the definitions of the error values and
defines gdbm_errno as an external variable.)

\fIgdbm_version\fR is the string containing the version information.

There are a few more things of interest.  First, \fBgdbm\fR files are
not "sparse".  You can copy them with the UNIX \fBcp(1)\fR command and
they will not expand in the copying process.  Also, there is a
compatibility mode for use with programs that already use UNIX
\fBdbm\fR.  In this compatibility mode, no \fRgdbm\fR file pointer is
required by the programmer, and only one file may be opened at a time.
All users in compatibility mode are assumed to be writers.  If the
\fBgdbm\fR file is a read only, it will fail as a writer, but will
also try to open it as a reader.  All returned pointers in datum
structures point to data that \fBgdbm\fR WILL free.  They should be
treated as static pointers (as standard UNIX \fBdbm\fR does).
.SH LINKING
This library is accessed by specifying \fI\-lgdbm\fR as the last
parameter to the compile line, e.g.:
.sp
.nf
.in +5
gcc \-o prog prog.c \-lgdbm
.in
.fi
.PP
If you wish to use the \fBdbm\fR or \fBndbm\fR compatibility routines,
you must link in the \fIgdbm_compat\fR library as well.  For example:
.sp
.nf
.in +5
gcc \-o prog proc.c \-lgdbm \-lgdbm_compat
.in
.fi
.\" .SH BUGS

.SH "BUG REPORTS"
Send bug reports to <bug\-gdbm@gnu.org>.
.SH "SEE ALSO"
.BR gdbm_dump (1),
.BR gdbm_load (1),
.BR gdbmtool (1).
.SH AUTHORS
by Philip A. Nelson, Jason Downs and Sergey Poznyakoff.
.SH COPYRIGHT
Copyright \(co 1990 - 2011 Free Software Foundation, Inc.

GDBM is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.

GDBM is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GDBM.  If not, see <http://gnu.org/licenses/gpl.html>
.SH CONTACTS
You may contact the original author by:
.br
   e-mail:  phil@cs.wwu.edu
.br
  us-mail:  Philip A. Nelson
.br
Computer Science Department
.br
Western Washington University
.br
Bellingham, WA 98226

You may contact the current maintainers by:
.br
   e-mail:  downsj@downsj.com
.br
and
   e-mail:  gray@gnu.org

.\" Local variables:
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.\" time-stamp-start: ".TH GDBM 3 \""
.\" time-stamp-format: "%:B %:d, %:y"
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