def wal_archive(self, wal_path, concurrency=1):
        """
        Uploads a WAL file to S3 or Windows Azure Blob Service

        This code is intended to typically be called from Postgres's
        archive_command feature.
        """

        # Upload the segment expressly indicated.  It's special
        # relative to other uploads when parallel wal-push is enabled,
        # in that it's not desirable to tweak its .ready/.done files
        # in archive_status.
        xlog_dir = os.path.dirname(wal_path)
        segment = WalSegment(wal_path, explicit=True)
        uploader = WalUploader(self.layout, self.creds, self.gpg_key_id)
        group = WalTransferGroup(uploader)
        group.start(segment)

        # Upload any additional wal segments up to the specified
        # concurrency by scanning the Postgres archive_status
        # directory.
        started = 1
        seg_stream = WalSegment.from_ready_archive_status(xlog_dir)
        while started < concurrency:
            try:
                other_segment = next(seg_stream)
            except StopIteration:
                break

            if other_segment.path != wal_path:
                group.start(other_segment)
                started += 1

        try:
            # Wait for uploads to finish.
            group.join()
        except EnvironmentError as e:
            if e.errno == errno.ENOENT:
                print(e)
                raise UserException(
                    msg='could not find file for wal-push',
                    detail=('The operating system reported: {0} {1}'
                            .format(e.strerror, repr(e.filename))))
            raise
Uploads a WAL file to S3 or Windows Azure Blob Service

        This code is intended to typically be called from Postgres's
        archive_command feature.