[Developers] Cursor format change on sandbox, coming soon to freebase.com

[Scott Meyer]

Our just-completed software update of sandbox.freebase.com
has a cursor-format change.  Basically, cursors created with
against the previous sandbox software will not work against
the new software.  If you created a cursor before 4pm PST
today, attempts to use it will now generate an error.  The
recovery is to restart the cursored query from the beginning.

The cause of the incompatibility are some new optimizations
to graphd which deliver a 2x performance increase for certain
queries.

Our intention is that cursors have an indefinite but relatively
short lifespan.  We're making the format more resistant to
incompatibilities, but the information stored in a cursor
is intimately related to the capabilities of our query optimizer.
Faster queries may come at the expense of cursor format
compatibility, and recovery (for example, by silently rerunning
the queries producing the first N pages) may not always
be feasible.

If you're using long-running cursored queries, or contemplating
such, we'd love to hear from you.

-Scott