Re: crash on 8.2 and cvshead - failed to add item to the

Tom Lane wrote:
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
>> To see what's going on, I added some logs to the split code to print out
>> the free space on both halves as calculated by findsplitloc, and the
>> actual free space on the pages after split. I'm seeing a discrepancy of
>> 4 bytes on the right half; actual space free on right page after split
>> is 4 bytes less than anticipated.
>
> Hm, mis-counting the positions of itempointers maybe?

Found it:

/* Count up total space in data items without actually scanning 'em */
dataitemtotal = rightspace - (int) PageGetFreeSpace(page);

This is 4 bytes off, because PageGetFreeSpace subtracts
sizeof(ItemIdData) from the actual free space on page. We could do

dataitemtotal = rightspace - ((int) PageGetFreeSpace(page)
+sizeof(ItemIdData));

but that again would be 4 bytes off in the other direction if there's 0
bytes left on the page :(.

IMHO the right fix is to modify PageGetFreeSpace not to do the
subtraction, it's a hack anyway, but that means we have to go through
and fix every caller of it. Or we can add a new PageGetReallyFreeSpace
function and keep the old one for compatibility. What do we want?

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com