Re: New significance of holdable result sets in Java 8

Marko,

When you say holdable cursors are you referring to a holdable cursor
outside of a transaction? It seems so because the transaction commits after
leaving the service layer ?

If so these are not without significant cost on the server side.

Dave Cramer

dave.cramer(at)credativ(dot)ca
http://www.credativ.ca

On 12 November 2014 10:22, Marko Topolnik <marko(dot)topolnik(at)gmail(dot)com> wrote:

> As of the release of Java 8 and its Streams API a new door has opened for
> many things, including an important improvement in the way RESTful services
> can be implemented. Let me briefly describe the architecture with Spring's
> REST support: an MVC framework is used where the Controller dispatches the
> HTTP request to a Service method; the Service method contacts the database
> and returns a Model-oriented representation of the response; the View layer
> then transforms it into the actual HTTP response bytes.
>
> Data is passed from Controller to View as the return value of a method.
> Traditionally, if you wanted a collection-shaped response, you would return
> a List. This meant eager loading of all data needed for the response, which
> caused scalability issues related to the JVM heap space.
>
> With the Streams API it is now very convenient to return a
> lazily-evaluated stream of Model objects. It is also very convenient to
> make this stream pull data directly from an underlying ResultSet,
> tronsforming each row on-the-fly into a Model object. This, however, calls
> for holdable result sets because the transaction commits when program
> control leaves the Service layer.
>
> The Spring team has recognized the relevance of the above use case and
> with release 4.1.2 they have introduced a specific enhancement needed to
> support result sets holdable into the View layer (albeit only when JDBC is
> used over Hibernate). This is described in the issue SPR-12349 [1]. Spring
> also plans to support this use case with additional helper code which turns
> Hibernate's ScrollableResults into a Stream (SPR-12388 [2]).
>
> The above could raise the level of interest of the PostgreSQL JDBC team in
> implementing holdable result sets backed by native holdable cursors instead
> of the current client-side cursors, which don't allow the space complexity
> to be reduced from O(n) to O(1) on the JVM side. I am aware that this is
> not a trivial endeavor as it requires intervention into the FE/BE protocol,
> but I would nevertheless propose that this concern be reassessed in the
> light of new developments in the Java ecosystem.
>
> Regards,
> Marko Topolnik
>
>
>
> [1] https://jira.spring.io/browse/SPR-12349
> [2] https://jira.spring.io/browse/SPR-12388
>
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