On Mon, Sep 15, 2014 at 8:38 AM, Kouhei Kaigai <kai...@ak.jp.nec.com> wrote: >> > The only reason why I put separate hooks here is, create_custom_scan() >> > needs to know exact size of the CustomScan node (including private >> > fields), however, it is helpful for extensions to kick its callback to >> > initialize the node next to the common initialization stuff. >> >> Why does it need to know that? I don't see that it's doing anything that >> requires knowing the size of that node, and if it is, I think it shouldn't >> be. That should get delegated to the callback provided by the custom plan >> provider. >> > Sorry, my explanation might be confusable. The create_custom_scan() does not > need to know the exact size of the CustomScan (or its inheritance) because of > the two separated hooks; one is node allocation time, the other is the tail > of the series of initialization. > If we have only one hook here, we need to have a mechanism to informs > create_custom_scan() an exact size of the CustomScan node; including private > fields managed by the provider, instead of the first hook on node allocation > time. In this case, node allocation shall be processed by create_custom_scan() > and it has to know exact size of the node to be allocated. > > How do I implement the feature here? Is the combination of static node size > and callback on the tail more simple than the existing design that takes two > individual hooks on create_custom_scan()?
I still don't get it. Right now, the logic in create_custom_scan(), which I think should really be create_custom_plan() or create_plan_from_custom_path(), basically looks like this: 1. call hook function CreateCustomPlan 2. compute values for tlist and clauses 3. pass those values to hook function InitCustomScan() 4. call copy_path_costsize What I think we should do is: 1. compute values for tlist and clauses 2. pass those values to hook function PlanCustomPath(), which will return a Plan 3. call copy_path_costsize create_custom_scan() does not need to allocate the node. You don't need the node to be allocated before computing tlist and clauses. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
