Ühel kenal päeval, K, 2006-08-09 kell 10:57, kirjutas Tom Lane:
> Hannu Krosing <hannu@skype.net> writes:
> > Ühel kenal päeval, K, 2006-08-09 kell 12:56, kirjutas Simon Riggs:
> >> Methinks it should be the Write pointer all of the time, since I can't
> >> think of a valid reason for wanting to know where the Insert pointer is
> >> *before* we've written to the xlog file. Having it be the Insert pointer
> >> could lead to some errors.
>
> > What is the difference ?
>
> Insert points to the next byte to be written within the internal WAL
> buffers. The byte(s) preceding it haven't necessarily gotten out of
> those buffers yet. Write points to the end of what we've actually
> written to the kernel,
I assume that it also points to the byte after what is written to
kernel, or is it tha last byte written ?
> and there's also a Flush pointer that points
> to the end of what we believe is down on disk.
>
> Simon's point is that if you're going to use pg_current_xlog_location()
> to control partial shipping of xlog files, you probably want to know
> about the Write location, because that indicates the limit of what
> is visible to an external process.
Yes, that is what I need
> regards, tom lane
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