On Jun 11, 2008, at 10:42 AM, Heikki Linnakangas wrote:
Another issue is that it might not be possible to update a page for lack of space. Are we prepared to assume that there will never be a transformation we need to apply that makes the data bigger?We do need some solution to that. One idea is to run a pre-upgrade script in the old version that scans the database and moves tuples that would no longer fit on their pages in the new version. This could be run before the upgrade, while the old database is still running, so it would be acceptable for that to take some time.
That means old versions have to have some knowledge of new versions. There's also a big race condition unless the old version starts taking size requirements into account every time a page is dirtied.
No doubt people would prefer something better than that. Another idea would be to have some over-sized buffers that can be used as the target of conversion, until some tuples are moved off to another page. Perhaps the over-sized buffer wouldn't need to be in shared memory, if they're read-only until some tuples are moved.This is pretty hand-wavy, I know. The point is, I don't think these problems are insurmountable.
-- Decibel!, aka Jim C. Nasby, Database Architect [EMAIL PROTECTED] Give your computer some brain candy! www.distributed.net Team #1828
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