Section "43.7. Cursors” in the PL/pgSQL chapter of the doc (www.postgresql.org/docs/current/plpgsql-cursors.html#PLPGSQL-CURSOR-DECLARATIONS) starts with this:
« Rather than executing a whole query at once, it is possible to set up a cursor that encapsulates the query, and then read the query result a few rows at a time. One reason for doing this is to avoid memory overrun when the result contains a large number of rows. (However, PL/pgSQL users do not normally need to worry about that, since FOR loops automatically use a cursor internally to avoid memory problems.) A more interesting usage is to return a reference to a cursor that a function has created, allowing the caller to read the rows. This provides an efficient way to return large row sets from functions. » On its face, it seems to make sense. And I’ve written a few proof-of-concept tests. For example, I wrote a “security definer” function that's owned by a role that can select from the relevant table(s) that returns refcursor. And I called it from a subprogram that's owned by a role that cannot select from the relevant table(s) to loop through the rows. But I can't convince myself that this division of labor is useful. And especially I can't convince myself that the "pipeling" capability is relevant in a three-tier app with a stateless browser UI. Here, the paradigm has the client-side app checking out a connection from the pool, generating the entire response to the end-user's request, releasing the connection, and sending the response back to the browser. This paradigm isn't consistent with allowing the end user to navigate forwards and backwards in a scrollable cursor that is somehow held in its open state in in the sever by the the middle tier client on behalf of a browser session that comes back time and again to its dedicated middle tier client and thence yo its dedicated database server session. (Anyway, without anything like Oracle PL/SQL's packages, you have no mechanism to hold the opened cursor variable between successive server calls.) Is it fair to say that the PL/pgSQL refcursor is useful, at best, only in very special use-cases?
