On Mon, Dec 12, 2011 at 3:42 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Simon Riggs <simon@2ndQuadrant.com> writes:
>> On Mon, Dec 12, 2011 at 3:17 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Furthermore, what the XLR_BKP_REMOVABLE bit actually reports is just
>>> whether a backup operation is in progress, and I think we have now (or
>>> easily could) add reporting records to the WAL stream that tell when a
>>> backup starts or stops. So external compression would still be possible
>>> if it kept a bit more state around.
>>>
>>> So: is there actually any such compression program out there?
>>> Would anybody really cry if this flag went away?
>
>> Yes, WAL records could be invented to mark the boundaries, so yes,
>> IMHO it is OK to make that flag go away.
>
> It occurs to me also that we could just move the flag from
> per-WAL-record info bytes to per-page or even per-segment WAL headers.
> Because we now force a segment switch when starting a backup, the
> flag would be seen turned-on soon enough to prevent problems.
> Finding out that it's off again after the end of a backup might be
> a little delayed, but the only cost is failure to compress a few
> compressible records.
>
> I'm not volunteering to do the above, unless someone steps forward
> to say that there's active use of this flag, but either one of these
> solutions seems more tenable than using up an info-byte bit.
I'll volunteer. Assume you can reuse the flag and I will patch afterwards.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
