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.XE
.TH DB 3X
.SH NAME
DBopen, DBclose, DBget, DBput, DBdel, DBkey0, DBkeyn, DBlock, DBunlock, DBsync, DBapp, DBins, DBcopy \- database subroutines
.SH SYNOPSIS
.2C
.nf
.PP
.B #include <DB.h>
.PP
.B typedef struct {
.B "	char * dptr;"
.B "	int dsize;"
.B } datum;
.PP
.B int DBdebug;
.PP
.B DBFILE * DBopen(file, flags)
.B char * file;
.B int flags;
.PP
.B datum DBget(dp, key)
.B DBFILE * dp;
.B datum key;
.PP
.B int DBput(dp, key, content)
.B DBFILE * dp;
.B datum key, content;
.PP
.B int DBdel(dp, key)
.B DBFILE * dp;
.B datum key;
.PP
.B datum DBkey0(dp)
.B DBFILE * dp;
.PP
.B datum DBkeyn(dp, key)
.B DBFILE * dp;
.B datum key;
.PP
.B void DBclose(dp)
.B DBFILE * dp;
.PP
.B int DBlock(dp)
.B DBFILE * dp;
.PP
.B int DBunlock(dp)
.B DBFILE * dp;
.PP
.B void DBsync(dp)
.B DBFILE * dp;
.PP
.B int DBapp(dp, key, content)
.B DBFILE * dp;
.B datum key, content;
.PP
.B int DBins(dp, key, content)
.B DBFILE * dp;
.B datum key, content;
.PP
.B int DBcopy(sdp, ddp)
.B DBFILE * sdp, ddp;
.1C
.fi
.SH DESCRIPTION
These functions maintain key/content pairs in a data base.
The functions will handle databases as large as the filesystem can
handle and will access a keyed item in one or two file system
accesses.
The functions are obtained with the loader option
.BR \-lDB .
.PP
.IR Key s
and
.IR content s
are described by the
.I datum
typedef.
A
.I datum
specifies a string of
.I dsize
bytes pointed to by
.I dptr.
Arbitrary binary data, as well as normal ASCII strings, are allowed as
either keys or records.
The data base is stored in two files.
One file is a directory containing a bit map and has `.dir' as its
suffix.
The second file contains all data and has `.pag' as its suffix.
.PP
Before a database can be accessed, it must be opened by
.IR DBopen .
At the time of this call, the files
.IB file .dir
and
.IB file .pag
must exist unless the
.I DB_CREATE
flag is set in the flags argument.
If this flag is specified and the files exist, they are truncated.
The only other meaningful flag that may be specified is
.IR DB_RONLY ,
which indicates that the DB library may not write on the files.
If the files are both not writable, this flag need not be specified and the
.I d_flags
member of the returned DBFILE pointer will have this bit set.
Note that these flags are mutually exclusive, and if one must be
ignored, it will be
.IR DB_RONLY .\ 
.PP
Once open, the data stored under a key is accessed by
.I DBget
and data is placed under a key or overwritten by
.IR DBput .
The data denoted by a key may be appended to, or inserted before, by
.I DBapp
and
.IR DBins ,
respectively.
A key (and its associated contents) is deleted by
.IR DBdel .
A linear pass through all keys in a database may be made, in an
(apparently) random order, by use of
.I DBkey0
and
.IR DBkeyn .
.I DBkey0
will return the first key in the database.
With any key argument,
.I DBkeyn
will return the next key in the database.
This code will traverse the data base:
.IP
for (key = DBkey0(dp); key.dptr != NULL; key = DBkeyn(dp, key))
.PP
.I DBcopy
copies the data indicated by keys in the database referred to by its
first argument to the database indicated by its second argument using
the same traversal.
.PP
.I DBlock
and
.I DBunlock
set and clear advisory locks (see
.IR ioctl (4))
on the database files.
.I DBlock
returns when the lock is set by the invoking process.
.PP
.I DBsync
flushes any modified buffers, and is called by
.I DBunlock
and
.IR DBclose .
.SH DIAGNOSTICS
All functions that return an
.I int
indicate errors with negative values.
A zero return indicates success.
Routines that return a
.I datum
indicate errors with a null (0)
.I dptr.
.PP
.I DBput
will return an error in the event that a disk block fills with
inseparable data.
.PP
Debugging information will be printed out on
.I stderr
if
.I DBdebug
is set to one of
.IR DBDBCORE ,
.IR DBDBERR ,
.IR DBDBWARN ,
or
.IR DBDBINFO .
These values provide increasing amounts of information, ranging from
conditions that will cause abnormal termination of the program
.IR "" ( DBDBCORE )
to call traces of the user-accessible routines
.IR "" ( DBDBINFO ).
.SH BUGS
The `.pag' file will contain holes so that its apparent size is about
four times its actual content.
Older UNIX systems may create real file blocks for these holes when
touched.
These files cannot be copied by normal means
.IR "" ( cp (1),
.IR cat (1),
.IR tp (1),
.IR tar (1),
.IR ar (1))
without filling in the holes.
A command to permit copying of these files (with holes intact) is
provided
.IR "" ( DBcp (1)).\ 
.PP
.I Dptr
pointers returned by these subroutines point into static storage that
is changed by subsequent calls.
.PP
The sum of the sizes of a key/content pair must not exceed the internal
block size (currently 65536 (64K) bytes).
Moreover, all key/content pairs that hash together must fit on a single
block.
.PP
.I DBdel
does not physically reclaim file space, although it does make it
available for reuse.
Use
.IR DBcp (1)
or
.I DBcopy
if file space must be reclaimed.
.PP
The order of keys presented by
.I DBkey0
and
.I DBkeyn
depends on a hashing function, not on anything interesting.
.PP
Since these routines use binary data for internal housekeeping,
databases created on a VAX cannot be directly manipulated on a 3B, and
vice versa.
.IR DBcvt (1)
converts a database generated on either of these machines to a form
palatable on the other.
.SH "SEE ALSO"
.IR DB (1),
.IR DBcp (1),
.IR DBcvt (1).