1# @(#)README 8.1 (Berkeley) 6/4/93 2# $FreeBSD: head/lib/libc/db/hash/README 190498 2009-03-28 07:31:02Z delphij $ 3 4This package implements a superset of the hsearch and dbm/ndbm libraries. 5 6Test Programs: 7 All test programs which need key/data pairs expect them entered 8 with key and data on separate lines 9 10 tcreat3.c 11 Takes 12 bucketsize (bsize), 13 fill factor (ffactor), and 14 initial number of elements (nelem). 15 Creates a hash table named hashtest containing the 16 keys/data pairs entered from standard in. 17 thash4.c 18 Takes 19 bucketsize (bsize), 20 fill factor (ffactor), 21 initial number of elements (nelem) 22 bytes of cache (ncached), and 23 file from which to read data (fname) 24 Creates a table from the key/data pairs on standard in and 25 then does a read of each key/data in fname 26 tdel.c 27 Takes 28 bucketsize (bsize), and 29 fill factor (ffactor). 30 file from which to read data (fname) 31 Reads each key/data pair from fname and deletes the 32 key from the hash table hashtest 33 tseq.c 34 Reads the key/data pairs in the file hashtest and writes them 35 to standard out. 36 tread2.c 37 Takes 38 butes of cache (ncached). 39 Reads key/data pairs from standard in and looks them up 40 in the file hashtest. 41 tverify.c 42 Reads key/data pairs from standard in, looks them up 43 in the file hashtest, and verifies that the data is 44 correct. 45 46NOTES: 47 48The man page ../man/db.3 explains the interface to the hashing system. 49The file hash.ps is a postscript copy of a paper explaining 50the history, implementation, and performance of the hash package. 51 52"bugs" or idiosyncracies 53 54If you have a lot of overflows, it is possible to run out of overflow 55pages. Currently, this will cause a message to be printed on stderr. 56Eventually, this will be indicated by a return error code. 57 58If you are using the ndbm interface and exit without flushing or closing the 59file, you may lose updates since the package buffers all writes. Also, 60the db interface only creates a single database file. To avoid overwriting 61the user's original file, the suffix ".db" is appended to the file name 62passed to dbm_open. Additionally, if your code "knows" about the historic 63.dir and .pag files, it will break. 64 65There is a fundamental difference between this package and the old hsearch. 66Hsearch requires the user to maintain the keys and data in the application's 67allocated memory while hash takes care of all storage management. The down 68side is that the byte strings passed in the ENTRY structure must be null 69terminated (both the keys and the data). 70