Re: Weird behavior with "sensitive" cursors.

Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Interesting. If I create an non-unique index on the table before
> declaring the cursor, FETCH throws an error:

> alvherre=# fetch all from c1;
> ERROR: attempted to lock invisible tuple

I get that in 8.4 and HEAD even without any index, just trying the given
case. It looks to me like this is a bug in the new snapshot management.
The cursor is using CurrentSnapshot directly --- it does not have a
private copy --- and therefore when CommandCounterIncrement happens
it affects what the cursor can "see". The cursor should not be able
to "see" any tuples created after it was created.

I think we need to ensure that when a cursor is created, it obtains a
private copy of the current snapshot ... but I'm not sure where that
ought to happen. Thoughts?

regards, tom lane