On Sep26, 2011, at 11:50 , Fujii Masao wrote:
> Currently, if a reference to an invalid page is found during recovery,
> its information
> is saved in hash table "invalid_page_tab". Then, if such a reference
> is resolved,
> its information is removed from the hash table. If there is unresolved
> reference to
> an invalid page in the hash table at the end of recovery, PANIC error occurs.
> What I'm worried about is that the hash table is volatile. If a user restarts
> the server before reaching end of recovery, any information in the
> hash table is lost,
> and we wrongly miss the PANIC error case because we cannot find any unresolved
> reference. That is, even if database is corrupted at the end of recovery,
> a user might not be able to notice that. This looks like a serious problem. 
> No?
> To prevent the above problem, we should write the contents of the hash table 
> to
> the disk for every restartpoints, I think. Then, when the server
> starts recovery,
> it should reload the hash table from the disk. Thought? Am I missing 
> something?

Shouldn't references to invalid pages only occur before we reach a consistent
state? If so, the right fix would be to check whether all invalid page 
have been resolved after we've reached a consistent state, and to skip creating
restart points while there're unresolved page references.

best regards,
Florian Pflug

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