On Thursday 11 February 2010 11:10:32 Simon Riggs wrote: > On Mon, 2010-02-08 at 04:33 +0000, Tom Lane wrote: > > We still have to retain all code that copes with finding > > HEAP_MOVED_OFF and HEAP_MOVED_IN flag bits on existing tuples. This > > can't be removed as long as we want to support in-place update from > > pre-9.0 databases. > > This doesn't seem to be a great reason. Letting weird states exist is > not a feature, its a risk. Let me explain. > > This would only happen if a VACUUM FULL had been run on the pre-9.0 > database and it had failed part way through. Re-VACUUMing would remove > those settings. > > ISTM that that the upgrade process should cover this, not force the > server to cope with rare and legacy situations. If we do not do this, > then we might argue it should *never* be removed because this same rare > situation can persist into 9.1 etc.. > > There were data loss situations possible in early 8.4 and these > persisted into later releases *because* the minor release upgrade > process did not contain a scan to detect and remove the earlier > problems. If we allow tuples to be in strange legacy states we greatly > increase the difficulty of diagnosing and fixing problems. People will > say "moved in/off can be ignored now" and mistakes will happen. > > We should remove the moved in/off flag bits and make it a part of the > upgrade process to ensure the absence of those states. Essentially requiring a successfull VACUUM FULL or CLUSTER on all tables is imho in the same ballpark as requiring a dump+restore timewise on bigger databases.
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