On Sat, Feb 25, 2017 at 10:00 AM, Kohei KaiGai <kaigai@kaigai.gr.jp> wrote:
> I tried to add a description how custom-scan callbacks performs under the
> executor, and when invoked roughly.
> However, it is fundamentally not easy for most of people because it assumes
> FDW/CSP author understand the overall behavior of optimizer / executor, not
> only APIs specifications.
I think the statements about Shutdown only being useful in parallel
mode aren't quite striking the right tone. In theory a node can hold
any kind of resources and find it worthwhile to release them at
shutdown time. I think we'll eventually find it useful to run
shutdown callbacks in other cases as well - e.g. when a Limit has been
filled. It's probably true that the undeniable need for this today is
in the parallel query case, but I'd like to have this text read in a
way that doesn't assert that this is the only possible use case,
because I don't think it is.
I rewrote the documentation along those lines a bit and committed this.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
