On 8/27/12 12:40 PM, Robert Haas wrote:
On Sat, Aug 25, 2012 at 1:30 PM, David Johnston<pol...@yahoo.com> wrote:
>My internals knowledge is basically zero but it would seem that If you
>simply wanted the end-of-transaction result you could just record nothing
>during the transaction and then copy whatever values are present at commit
>to whatever logging mechanism you need.
"Whatever values are present and commit" could be a terabyte of data.
Or it could be a kilobyte of changed data within a terabyte database.
You'd need some way to identify which data actually needs to be
copied, since you surely don't want to copy the whole database. And
even if you can identify it, going back and visiting all those blocks
a second time will be expensive.
This makes me think about the original time travel, which was to not
automatically remove old tuple versions.
I think it would be interesting to look at allowing old tuples to be visible as
well as doing something different when vacuum comes around.
--
Jim C. Nasby, Database Architect j...@nasby.net
512.569.9461 (cell) http://jim.nasby.net
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