=head1 NAME

RocksDB::CompactionFilter - rocksdb::CompactionFilter object

=head1 SYNOPSIS

  use RocksDB;

  my $handler = MyCompactionFilter->new;
  my $db = RocksDB->new('/path/to/db', {
      create_if_missing => 1,
      compaction_filter => RocksDB::CompactionFilter->new($handler),
  });

=head1 DESCRIPTION

B<RocksDB::CompactionFilter> is a utility class to make rocksdb::CompactionFilter object.

=head1 CONSTRUCTOR

=head2 C<< RocksDB::CompactionFilter->new($handler :Object) :RocksDB::CompactionFilter >>

Create and return a new RocksDB::CompactionFilter object.

The $handler must respond to 'filter'.

See 'HANDLER METHODS' section for more details.

=head1 HANDLER METHODS

=head2 C<< $handler->filter($level :Int, $key :Str, $existing_value :Maybe[Str], $new_value_ref :Str) :Bool >>

The compaction process invokes this method for kv that is being compacted.
A return value of false indicates that the kv should be preserved in the
output of this compaction run and a return value of true indicates that
this key-value should be removed from the output of the compaction.
The application can inspect the existing value of the key and make
decision based on it.

When the value is to be preserved, the application has the option
to modify the existing_value and pass it back through new_value_ref.

If multithreaded compaction is being used *and* a single CompactionFilter
instance was supplied via compaction_filter, this method may be
called from different threads concurrently.  The application must ensure
that the call is thread-safe.

If the CompactionFilter was created by a factory, then it will only ever
be used by a single thread that is doing the compaction run, and this
call does not need to be thread-safe.  However, multiple filters may be
in existence and operating concurrently.

=head1 SEE ALSO

L<RocksDB>

=head1 AUTHOR

Jiro Nishiguchi E<lt>jiro@cpan.orgE<gt>

=cut