Chapter 16. A Database Library

	Example	Relevant Functions
16.1	Concurrent database Library Usage example of database functions. Create a database and write 3 records to it.	db_open, db_store, db_close, err_sys (Stevens' lib), err_quit (Stevens' lib), exit
16.2	db.h Header file defining the DB interfaces The database is decentralized (handled by multiple processes in parallel). Locking is fine-grained (hash-chain based): multiple readers and one writer are allowed on each hash chain.	Functions appear below
16.3	db_open Open or create a database Same arguments as open(2)	strlen, strcpy, strcat, sprintf, open, write, fstat, _db_alloc, _db_free, db_rewind, err_dump, err_sys (Stevens' lib), writew_lock, un_lock (Stevens' lib),
16.4	_db_alloc Allocate and initialize a DB structure Internal (not an interface) function.	calloc, malloc, err_dump (Stevens' lib),
16.5	_db_free Free up a DB structure, including all malloc'ed buffers it may point to. Also close any open file descriptors Internal (not an interface) function.	close, free, err_dump (Stevens' lib)
16.6	db_close User callable wrapper for _db_free which does all closing/freeing	_db_free
16.7	db_fetch fetch a specified record from DB	_db_find, _db_readdat, un_lock (Stevens' lib), err_dump (Stevens' lib)
16.8	_db_find Find a specified record in the DB Called by db_delete, db_fetch, and db_store	writew_lock (Stevens' lib), readw_lock (Stevens' lib), un_lock (Stevens' lib), err_dump (Stevens' lib), _db_hash, _db_readptr, _db_readidx, strcmp
16.9	_db_hash.c Calculate the hash value of a key. May replace by more sophisticated versions Internal (not an interface) function.	none (simple arithmetic)
16.10	_db_readptr Return a chain pointer from the index file The chain can be a free-list pointer, a hash table chain ptr, or an index record chain ptr. Internal (not an interface) function.	lseek, read, atol, err_dump (Stevens' lib)
16.11	_db_readidx Reads each index record and divides it into apropriate fields. Internal (not an interface) function.	lseek, readv, read, atol, atoi, strchr, err_dump (Stevens' lib)
16.12	_db_readdat Read current data record into the data buffer Return pointer to null terminated data buffer Internal (not an interface) function.	lseek, read, err_dump (Stevens' lib)
16.13	db_delete Delete the specified record	_db_find, _db_dodelete, un_lock (Stevens' lib), err_dump (Stevens' lib),
16.14	_db_dodelete Delete current record specified by the db structure. Called by db_delete, and db_store after record has been located by _db_find Internal (not an interface) function.	writew_lock (Stevens' lib), _db_writedat, _db_writeidx, _db_readptr, _db_writeptr, un_lock (Stevens' lib), err_dump (Stevens' lib),
16.15	_db_writedat Write a data record Called by _db_dodelete (to write a blank record) and by db_store Internal (not an interface) function.	writew_lock (Stevens' lib), un_lock (Stevens' lib), err_dump (Stevens' lib), lseek, strlen, writev
16.16	_db_writeidx Write an index record Internal (not an interface) function.	err_quit (Stevens' lib), err_dump (Stevens' lib), writew_lock (Stevens' lib), un_lock (Stevens' lib), sprintf, strlen, lseek, writev
16.17	_db_writeptr Write a chain ptr field somewhere in the index file: The free list, the hash table, or an index record. Internal (not an interface) function.	err_quit (Stevens' lib), err_dump (Stevens' lib), sprintf, lseek, write
16.18	db_store Store a record in the DB. Check if exists (for replace data case), find the record (or a free location in free list), lock the chain, and update (or insert) it.	strlen, un_lock (Stevens' lib), err_dump (Stevens' lib), _db_find, _db_findfree, _db_readptr, _db_writedat, _db_writeidx, _db_writeptr, _db_dodelete
16.19	_db_findfree Find a free index record and an acompanying data record of correct sizes. Called only by db_store Internal (not an interface) function.	writew_lock (Stevens' lib), err_dump (Stevens' lib), un_lock (Stevens' lib), _db_readptr, _db_writeptr, _db_readidx, strlen
16.20	db_rewind Prepare DB for sequential read. Silently called by db_open. Must be called before the first db_nextrec	lseek, err_dump (Stevens' lib)
16.21	db_nextrec Advance to next record (for sequential DB access)	readw_lock (Stevens' lib), un_lock (Stevens' lib), err_dump (Stevens' lib), _db_readidx, _db_readdat, strcpy