Re: walsender vs. XLogBackgroundFlush during shutdown

Now, this situation is apparently expected, because WalSndWaitForWal()
does this:

    /*
     * If we're shutting down, trigger pending WAL to be written out,
     * otherwise we'd possibly end up waiting for WAL that never gets
     * written, because walwriter has shut down already.
     */
    if (got_STOPPING)
        XLogBackgroundFlush();

but unfortunately that does not actually do anything, because right at
the very beginning XLogBackgroundFlush() does this:

    /* back off to last completed page boundary */
    WriteRqst.Write -= WriteRqst.Write % XLOG_BLCKSZ;

That is, it intentionally ignores the incomplete page, which means the
walsender can't read the record and reach GetFlushRecPtr().

XLogBackgroundFlush() does this since (at least) 2007, so how come we
never had issues with this before?