Employ transaction_read_only

[danolivo]

Hi,

I wonder why you use your own control [1] over the existing XactReadOnly machinery? It seems to me that it would be enough if your GUC just changed and restored this value in the backend on Executor Start (potentially, during planning/parsing) - the standard ExecCheckXactReadOnly() should prevent DML/DDL executions ...

Also, I think for the replication apply workers, this restriction might be implemented through a SMGR hook somehow.

[1]

pg_readonly/pg_readonly.c

Line 454 in ea52059

ereport(ERROR, (errmsg("pg_readonly: pgro_exec: invalid statement because cluster is read-only")));