[OSM-dev] Minute Diffs Broken

Greg Troxel gdt at ir.bbn.com
Tue May 5 02:29:52 BST 2009

Frederik Ramm <frederik at remote.org> writes:

> Hi,
> Greg Troxel wrote:
>> So obviously we aren't running "SET TRANSACTION ISOLATION LEVEL
>> SERIALIZABLE", since that would kill performance and make things harder,
>> but it would solve this :-)
> How so? The problem seems to be too much transaction isolation, not
> too little.

With select by time, it would still be buggy.  But if the select was
"all changesets > X" where X was the highest changeset in the previous
select, it would work, because there would have to be a total ordering
of transactions (at least as far as anyone can tell).  So the select of
highest would have to be in between two others, and the changeset id is
perhaps an auto-sequence, or else read/increment/write which again would
force ordering.

> If we were operating on a "dirty read" basis then Brett's
> diffs would not miss any data (but they would contain changes that
> were part of a transaction that was later rolled back).

Sure, that would be worse :-)
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