Re: bk commit into 4.1 tree (holyfoot:1.2679) BUG#30286

Hi holyfoot,

See my remarks below. The fix is generally OK with few requests for comments and more tests.

On 17.08.2007, at 13:29, holyfoot@mysql.com wrote:

> Below is the list of changes that have just been committed into a
> local
> 4.1 repository of hf. When hf does a push these changes will
> be propagated to the main repository and, within 24 hours after the
> push, to the public repository.
> For information on how to access the public repository
> see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html
>
> ChangeSet@1.2679, 2007-08-17 15:29:47+05:00, holyfoot@mysql.com +3 -0
> Bug #30286 spatial index cause corruption and server crash!
>
> Sometimes the result of the DOUBLE claculations can be bigger
> than DBL_MAX constant we use in code. If that happens in
> rtree_pick_key it can fail as it cannot find suitable key.
>
> So we shouldn't use DBL_MAX constant as a biggest double we
> can ever get.

I don't think a valid double value can be greater than DBL_MAX (except +/-INF and NaN). Here we may have a NaN because of the way a key is selected : it tries to calculate the MBR area increase caused by adding the new polygon to the key (an operation that may overflow a double).
So as a result rtree_area_increase() returns NaN (and inf for its output parameter "ab_area"). And this is the key it doesn't find.

I suggest that you add a (very verbose) comment to rtree_area_increase () that explains why and when it can return NaN+inf and what does this mean.

Then please think about (and ideally add a test) what can happen if the first two keys on the page will trigger NaN+inf case for the same value added to them. Can there be such ? If yes, how does NaN compare to a NaN (i.e. which key to choose) ?

Obviously the commit comment needs rephrasing as well.

Do you need help?

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Other than that I don't see other problems with the fix.

Best Regards,
Joro

-- 
Georgi Kodinov, Senior Software Engineer
MySQL AB, Plovdiv, Bulgaria, www.mysql.com
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