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Interface differences between TDB1 and TDB2.
- tdb2 uses 'struct tdb_data', tdb1 uses 'struct TDB_DATA'. Use the
TDB_DATA typedef if you want portability between the two.
- tdb2 functions return 0 on success, and a negative error on failure,
whereas tdb1 functions returned 0 on success, and -1 on failure.
tdb1 then used tdb_error() to determine the error; this is also
supported in tdb2 to ease backwards compatibility, though the other
form is preferred.
- tdb2's tdb_fetch() returns an error, tdb1's returned the data directly
(or tdb_null, and you were supposed to check tdb_error() to find out why).
- tdb2's tdb_nextkey() frees the old key's dptr, in tdb1 you needed to do
this manually.
- tdb1's tdb_open/tdb_open_ex took an explicit hash size. tdb2's hash table
resizes as required.
- tdb2 uses a linked list of attribute structures to implement logging and
alternate hashes. tdb1 used tdb_open_ex, which was not extensible.
- tdb2 does locking on read-only databases (ie. O_RDONLY passed to tdb_open).
tdb1 did not: use the TDB_NOLOCK flag if you want to suppress locking.
- tdb2's log function is simpler than tdb1's log function. The string is
already formatted, and it takes an enum tdb_log_level not a tdb_debug_level,
and which has only three values: TDB_LOG_ERROR, TDB_LOG_USE_ERROR and
TDB_LOG_WARNING.
- tdb2 provides tdb_deq() for comparing two struct tdb_data.
- tdb2's tdb_name() returns a copy of the name even for TDB_INTERNAL dbs.
- tdb2 does not need tdb_reopen() or tdb_reopen_all(). If you call
fork() after during certain operations the child should close the
tdb, or complete the operations before continuing to use the tdb:
tdb_transaction_start(): child must tdb_transaction_cancel()
tdb_lockall(): child must call tdb_unlockall()
tdb_lockall_read(): child must call tdb_unlockall_read()
tdb_chainlock(): child must call tdb_chainunlock()
tdb_parse() callback: child must return from tdb_parse()
- tdb2 will not open a non-tdb file, even if O_CREAT is specified.
- There is no tdb_traverse_read. For operating on TDB1 files, you can
simulate it by tdb_add_flag(tdb, TDB_RDONLY); tdb_traverse();
tdb_remove_flag(tdb, TDB_RDONLY). This may be desirable because
traverse on TDB1 files use a write lock on the entire database
unless it's read-only.
- Failure inside a transaction (such as a lock function failing) does
not implicitly cancel the transaction; you still need to call
tdb_transaction_cancel().
TDB1 Compatibility:
- tdb2's offers a tdb1_incompatible_hash function, which is the same
as the default hash with the TDB_INCOMPATIBLE_HASH flag. There is
no way of marking an old TDB incompatible with versions < 1.2.6
while using any other hash.
- The TDB_ATTRIBUTE_TDB1_HASHSIZE attribute can be used to control the
hash size, but only when creating (ie. O_CREAT) a TDB1
(ie. TDB_VERSION1).
- There is no TDB_CLEAR_IF_FIRST flag; it has severe scalability and
API problems. If necessary, you can emulate this by using the open
hook and placing a 1-byte lock at offset 4. If your program forks,
you will need to place this lock again in the child.
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