On Tue, Aug 24, 2021 at 12:36 PM Pavel Stehule <pavel.steh...@gmail.com> wrote: > > There are few GUC variables, where we need extra fast access - work_mem, > encoding settings, and maybe an application name. For others I hadn't needed > to access it for over 20 years. But I understand that more complex extensions > like timescaledb will use more internal GUC.
Note that even trivial extensions require some other GUC access. For instance any single extension that wants to aggregate data based on the query_id has to store an array of query_id in shmem to know what a parallel worker is working on. On top of wasting memory and CPU, it also means that computing the maximum number of backends in required. So you need to recompute MaxBackends, which means access to multiple GUCs. Unfortunately the patch to expose the query_id didn't fix that problem as it only passes the top level query_id to the pararllel workers, not the current one.
