Re: 8.1 index corruption woes

On Jul 11, 2008, at 2:17 PM, Tom Lane wrote:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
>> I don't want to discard this idea, because we're getting a very
>> unusually high number of bogus entries.  However, they are all (or a
>> very high percentage of them) the very first entry on each index  
>> page.
>> I want to confirm that the leftmost on a leaf btree page is a valid
>> item, and not something like the lower bound value?  (I think we only
>> store high bounds on internal pages, not leaf pages, but I'm not  
>> sure).
>
> Er ... no.  Per nbtree/README:
>
> : On a page that is not rightmost in its tree level, the "high key" is
> : kept in the page's first item, and real data items start at item 2.
> : The link portion of the "high key" item goes unused.  A page that is
> : rightmost has no "high key", so data items start with the first  
> item.
> : Putting the high key at the left, rather than the right, may seem  
> odd,
> : but it avoids moving the high key as we add data items.
>
> (Right offhand, it looks like _bt_split just copies the item that it's
> cloning the index key of.  Maybe it would be worth setting the item
> pointer invalid, to prevent confusion in future?)

Another option would be to change pg_filedump to understand what the  
first item in the index is.
-- 
Decibel!, aka Jim C. Nasby, Database Architect  decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828