Thread: Get access to the whole query in CustomScan path callback
Hi,
The goal is to have access to all the tables that are being scanned or will be scanned as a part of the query. Basically, the callback looks like this:
typedef void (*set_rel_pathlist_hook_type) (PlannerInfo *root, RelOptInfo *rel, Index rti, RangeTblEntry *rte);Now, the problem is when there is a nested query, the function will be called once for the parent query and once for the subquery. However, I need access to the whole query in this function. There seems to be no CustomScan callback before this that has the whole query passed to it. Is there any way I can get access to the complete query (or all the relations in the query) by using the parameters passed to this function? Or any other workaround?
Thank you and happy holidays!
Amin <amin.fallahi@gmail.com> writes:
> The goal is to have access to all the tables that are being scanned or will
> be scanned as a part of the query. Basically, the callback looks like this:
> typedef void (*set_rel_pathlist_hook_type) (PlannerInfo *root,
> RelOptInfo *rel,
> Index rti,
> RangeTblEntry *rte);
> Now, the problem is when there is a nested query, the function will be
> called once for the parent query and once for the subquery. However, I need
> access to the whole query in this function. There seems to be no CustomScan
> callback before this that has the whole query passed to it. Is there any
> way I can get access to the complete query (or all the relations in the
> query) by using the parameters passed to this function? Or any other
> workaround?
Everything the planner knows is accessible via the "root" pointer.
I very strongly question the idea that a custom scan provider should
be doing what you say you want to do, but the info is there.
regards, tom lane
I cannot find any information related to other relations in the query other than the one which is being scanned in the root pointer. Is there any function call which can be used to get access to it?
On Wed, Dec 21, 2022 at 9:46 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Amin <amin.fallahi@gmail.com> writes:
> The goal is to have access to all the tables that are being scanned or will
> be scanned as a part of the query. Basically, the callback looks like this:
> typedef void (*set_rel_pathlist_hook_type) (PlannerInfo *root,
> RelOptInfo *rel,
> Index rti,
> RangeTblEntry *rte);
> Now, the problem is when there is a nested query, the function will be
> called once for the parent query and once for the subquery. However, I need
> access to the whole query in this function. There seems to be no CustomScan
> callback before this that has the whole query passed to it. Is there any
> way I can get access to the complete query (or all the relations in the
> query) by using the parameters passed to this function? Or any other
> workaround?
Everything the planner knows is accessible via the "root" pointer.
I very strongly question the idea that a custom scan provider should
be doing what you say you want to do, but the info is there.
regards, tom lane