Re: Fdw cleanup

Feng Tian wrote:
> I need some help to understand foreign table error handling.
>
> For a query on foreign table, ExecInitForeignScan is called, which in turn calls the BeginForeignScan
> hook.   Inside this hook, I allocated some resource,
>
>
> node->fdw_state = allocate_resource(...);
>
> If everything goes well, ExecEndForeignScan will call call my EndForeignScan hook, inside the hook, I
> free the resource.
>
> free_resource(node->fdw_state);
>
> However, if during the execution an error happened, seems to me that EndForeignScan will not be called
> (traced using gdb).   So my question is, is Begin/End the right place for allocate/free resources?
> If it is not, what is the right way to do this?

If the resource is memory, use "palloc" to allocate it, and PostgreSQL
will take care of it automatically.

Other than that, you could call RegisterXactCallback() and register a callback
that will be called upon transaction end.  In the callback function you can
free the resource if it was not already freed by EndForeignScan.

Yours,
Laurenz Albe