168 lines
5.6 KiB
Plaintext
168 lines
5.6 KiB
Plaintext
tdb - a trivial database system
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tridge@linuxcare.com December 1999
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==================================
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This is a simple database API. It was inspired by the realisation that
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in Samba we have several ad-hoc bits of code that essentially
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implement small databases for sharing structures between parts of
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Samba. As I was about to add another I realised that a generic
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database module was called for to replace all the ad-hoc bits.
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I based the interface on gdbm. I couldn't use gdbm as we need to be
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able to have multiple writers to the databases at one time.
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Compilation
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-----------
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add HAVE_MMAP=1 to use mmap instead of read/write
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add TDB_DEBUG=1 for verbose debug info
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add NOLOCK=1 to disable locking code
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Testing
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-------
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Compile tdbtest.c and link with gdbm for testing. tdbtest will perform
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identical operations via tdb and gdbm then make sure the result is the
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same
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Also included is tdbtool, which allows simple database manipulation
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on the commandline.
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tdbtest and tdbtool are not built as part of Samba, but are included
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for completeness.
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Interface
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---------
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The interface is very similar to gdbm except for the following:
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- different open interface. The tdb_open call is more similar to a
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traditional open()
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- no tdbm_reorganise() function
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- no tdbm_sync() function. No operations are cached in the library anyway
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- added a tdb_traverse() function for traversing the whole database
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A general rule for using tdb is that the caller frees any returned
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TDB_DATA structures. Just call free(p.dptr) to free a TDB_DATA
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return value called p. This is the same as gdbm.
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here is a full list of tdb functions with brief descriptions.
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----------------------------------------------------------------------
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TDB_CONTEXT *tdb_open(char *name, int hash_size, int tdb_flags,
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int open_flags, mode_t mode)
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open the database, creating it if necessary
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The open_flags and mode are passed straight to the open call on the database
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file. A flags value of O_WRONLY is invalid
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The hash size is advisory, use zero for a default value.
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return is NULL on error
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possible tdb_flags are:
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TDB_CLEAR_IF_FIRST - clear database if we are the only one with it open
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TDB_INTERNAL - don't use a file, instaed store the data in
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memory. The filename is ignored in this case.
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TDB_NOLOCK - don't do any locking
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TDB_NOMMAP - don't use mmap
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----------------------------------------------------------------------
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char *tdb_error(TDB_CONTEXT *tdb);
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return a error string for the last tdb error
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----------------------------------------------------------------------
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int tdb_close(TDB_CONTEXT *tdb);
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close a database
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----------------------------------------------------------------------
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int tdb_update(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf);
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update an entry in place - this only works if the new data size
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is <= the old data size and the key exists.
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on failure return -1
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----------------------------------------------------------------------
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TDB_DATA tdb_fetch(TDB_CONTEXT *tdb, TDB_DATA key);
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fetch an entry in the database given a key
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if the return value has a null dptr then a error occurred
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caller must free the resulting data
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----------------------------------------------------------------------
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int tdb_exists(TDB_CONTEXT *tdb, TDB_DATA key);
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check if an entry in the database exists
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note that 1 is returned if the key is found and 0 is returned if not found
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this doesn't match the conventions in the rest of this module, but is
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compatible with gdbm
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----------------------------------------------------------------------
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int tdb_traverse(TDB_CONTEXT *tdb, int (*fn)(TDB_CONTEXT *tdb,
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TDB_DATA key, TDB_DATA dbuf, void *state), void *state);
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traverse the entire database - calling fn(tdb, key, data, state) on each
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element.
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return -1 on error or the record count traversed
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if fn is NULL then it is not called
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a non-zero return value from fn() indicates that the traversal should stop
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----------------------------------------------------------------------
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TDB_DATA tdb_firstkey(TDB_CONTEXT *tdb);
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find the first entry in the database and return its key
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the caller must free the returned data
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----------------------------------------------------------------------
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TDB_DATA tdb_nextkey(TDB_CONTEXT *tdb, TDB_DATA key);
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find the next entry in the database, returning its key
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the caller must free the returned data
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----------------------------------------------------------------------
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int tdb_delete(TDB_CONTEXT *tdb, TDB_DATA key);
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delete an entry in the database given a key
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----------------------------------------------------------------------
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int tdb_store(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf, int flag);
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store an element in the database, replacing any existing element
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with the same key
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If flag==TDB_INSERT then don't overwrite an existing entry
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If flag==TDB_MODIFY then don't create a new entry
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return 0 on success, -1 on failure
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----------------------------------------------------------------------
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int tdb_writelock(TDB_CONTEXT *tdb);
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lock the database. If we already have it locked then don't do anything
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----------------------------------------------------------------------
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int tdb_writeunlock(TDB_CONTEXT *tdb);
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unlock the database
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----------------------------------------------------------------------
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int tdb_lockchain(TDB_CONTEXT *tdb, TDB_DATA key);
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lock one hash chain. This is meant to be used to reduce locking
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contention - it cannot guarantee how many records will be locked
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----------------------------------------------------------------------
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int tdb_unlockchain(TDB_CONTEXT *tdb, TDB_DATA key);
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unlock one hash chain
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