[bind10-dev] initial ideas on the "difference" design

[Stephen Morris]

On 13/10/2011 07:19, JINMEI Tatuya / 神明達哉 wrote:

>> In general, the statement will be simpler in most cases the
>> versions required will not be "B to E" but "B to latest".  In
>> that case, something like:
>> 
>> select * from (select * from diffs where zone_id = Z and version
>> >= B except select * from diffs where zone id = Z and version = B
>> and operation = 1) order by id asc
>> 
>> That is not quite complete in itself as an additional access will
>> be required as we need to check that there is difference
>> information for version B in the table.  If there isn't, we have
>> to fall back to AXFR.
> 
> Cool, but note that we still cannot directly use the versions for 
> comparison unless we internally convert SOA serials to
> monotonically increase numbers.

I suppose there are two cases here:

1) For whatever reason, a server capable of IXFR-out is loaded with a
copy of the zone that has a lower-serial number than the current
version.  This is incorrect operational behaviour, but it could
happen.  Unless we allow some form of editing of the difference
sequences stored, I would argue that the simplest thing would be for
the server to drop all previous difference information if that were to
happen.

2) The rollover of the serial number (something I overlooked).  You
are right that we can't then compare serial numbers for greater/less
than, but we can do equality checks.  Assuming that we are just
wanting the differences for version B through to the latest version of
the zone, we would have something like:

select * from diffs where
zone_id = Z and
id >= (select id from diffs where
   zone_id = Z and version = B and operation = 0
   order by id asc limit 1)
order by id asc

Of course, there is the corner case where the serial starts at B and
is rolled through intermediate versions back to B.  If that were to
happen, again I think that the simplest thing would be to drop all
difference sequences for the first instance of B and earlier.

Stephen