HP-UX Reference (11i v1 00/12) - 3 Library Functions N-Z (vol 7)
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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man3/nan.3m
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ndbm(3X) ndbm(3X)
not provide the many other useful database functions that are found in more robust database management
systems. Creating and updating databases by use of these functions is relatively slow because of data
copies that occur upon hash collisions. These functions are useful for applications requiring fast lookup of
relatively static information that is to be indexed by a single key.
The pointer to data that is returned from these functions are not aligned. This can cause problems if the
block contains data that must be aligned to a specific boundry. If the block contains data that must be
aligned, the block should be copied to an appropriately aligned area.
The .pag file will contain holes so that its apparent size is about four times its actual content. Some older
UNIX systems create real file blocks for these holes when touched. These files cannot be copied by normal
means (such as cp(1), cat(1), tar(1), or ar(1)) without expansion.
dptr pointers returned by these subroutines point into static storage that is changed by subsequent calls.
The sum of the sizes of a key/content pair must not exceed the internal block size (currently 1024 bytes).
Moreover, all key/content pairs that hash together must fit on a single block. dbm_store returns an
error in the event that a disk block fills with inseparabledata.
dbm_delete does not physically reclaim file space, although it does make it available for reuse.
The order of keys presented by dbm_firstkey and dbm_nextkey
depends on a hashing function, not
on anything interesting.
A
dbm_store or dbm_delete during a pass through the keys by dbm_firstkey and
dbm_nextkey may yield unexpected results.
AUTHOR
ndbm(3X) was developed by the University of California, Berkeley.
SEE ALSO
dbm(3C).
Section 3−−540 − 2 − HP-UX Release 11i: December 2000
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