view release on metacpan or  search on metacpan

BDB.pm  view on Meta::CPAN

If you only ever use foreground requests (without a callback), this will
not be an issue (unless you use threads).

=head2 Unexpected Freezes or Deadlocks

Remember that, by default, BDB will execute requests in parallel, which
easily leads to deadlocks (even concurrent put's on the same database can
deadlock).

You either need to run deadlock detection (and handle the resulting
errors), or make sure only one process ever updates the database, ine one
thread, e.g. by using only foreground requests (without a callback).

=head1 FORK BEHAVIOUR

This module should do "the right thing" when the process using it forks:

Before the fork, BDB enters a quiescent state where no requests
can be added in other threads and no results will be processed. After
the fork the parent simply leaves the quiescent state and continues
request/result processing, while the child frees the request/result queue
(so that the requests started before the fork will only be handled in the
parent). Threads will be started on demand until the limit set in the
parent process has been reached again.

In short: the parent will, after a short pause, continue as if fork had
not been called, while the child will act as if BDB has not been used
yet.

Win32 note: there is no fork on win32, and perls emulation of it is too
broken to be supported, so do not use BDB in a windows pseudo-fork, better
yet, switch to a more capable platform.

=head1 MEMORY USAGE

Per-request usage:

Each aio request uses - depending on your architecture - around 100-200
bytes of memory. In addition, stat requests need a stat buffer (possibly
a few hundred bytes), readdir requires a result buffer and so on. Perl
scalars and other data passed into aio requests will also be locked and
will consume memory till the request has entered the done state.

This is not awfully much, so queuing lots of requests is not usually a
problem.

Per-thread usage:

In the execution phase, some aio requests require more memory for
temporary buffers, and each thread requires a stack and other data
structures (usually around 16k-128k, depending on the OS).

=head1 WIN32 FILENAMES/DATABASE NAME MESS

Perl on Win32 supports only ASCII filenames (the reason is that it abuses
an internal flag to store wether a filename is Unicode or ANSI, but that
flag is used for somethign else in the perl core, so there is no way to
detect wether a filename is ANSI or Unicode-encoded). The BDB module
tries to work around this issue by assuming that the filename is an ANSI
filename and BDB was built for unicode support.

=head1 KNOWN BUGS

Known bugs will be fixed in the next release, except:

   If you use a transaction in any request, and the request returns
   with an operating system error or DB_LOCK_NOTGRANTED, the internal
   TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
   above.

=head1 SEE ALSO

L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural
syntax), L<IO::AIO> (nice to have).

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut