Re: selecting large result sets in psql using cursors

Hi,

thanks for reviewing this :)

> > attached is the new and fixed version of the patch for selecting
> > large result sets from psql using cursors.
>
> The is_select_command bit is wrong because it doesn't allow for left
> parentheses in front of the SELECT keyword (something entirely
> reasonable when considering big union/intersect/except trees).
> Also you'd need to allow for VALUES as the first keyword.

You're right, I improved is_select_command to take these into account.
(Btw, I didn't even know a command VALUES existed..)

> But isn't the whole thing unnecessary? ISTM you could just ship the
> query with the DECLARE CURSOR prepended, and see whether you get a
> syntax error or not.

I find it neat that \u gives a good error message if someone
executes a non-select query. If I leave that out there is no way to tell
a real syntax error from one cause by executing non-selects...

Anyway, if we don't want the extra check, I can skip the
is_select_command call, of course.

Patch with fix against current CVS is attached.

> At some point we ought to extend libpq enough to expose the V3-protocol
> feature that allows partial fetches from portals; that would be a
> cleaner way to implement this feature. However since nobody has yet
> proposed a good API for this in libpq, I don't object to implementing
> \u with DECLARE CURSOR for now.
>
> BTW, \u seems not to have any mnemonic value whatsoever ... isn't there
> some other name we could use?

True :)
Since buffer commands all have a single char I wanted a single char one
too. The "c" for "cursor" was taken already, so i choose the "u" (second
char in "cursor"). If somebody has a better suggestion, let us know ;)

Bye, Chris.

PS: I'm traveling Fri 18th - Fri 25th and won't check mail often.

--

Chris Mair
http://www.1006.org