On 2025/06/01 17:34, Etsuro Fujita wrote:
postgres_fdw: Inherit the local transaction's access/deferrable modes. Previously, postgres_fdw always 1) opened a remote transaction in READ WRITE mode even when the local transaction was READ ONLY, causing a READ ONLY transaction using it that references a foreign table mapped to a remote view executing a volatile function to write in the remote side, and 2) opened the remote transaction in NOT DEFERRABLE mode even when the local transaction was DEFERRABLE, causing a SERIALIZABLE READ ONLY DEFERRABLE transaction using it to abort due to a serialization failure in the remote side. To avoid these, modify postgres_fdw to open a remote transaction in the same access/deferrable modes as the local transaction. This commit also modifies it to open a remote subtransaction in the same access mode as the local subtransaction. Although these issues exist since the introduction of postgres_fdw, there have been no reports from the field. So it seems fine to just fix them in master only.
I'm not sure this change should be considered a bug fix, since the current behavior of postgres_fdw with a local read-only transaction isn't clearly documented. Some users might see this as a behavioral change rather than a fix. Anyway if we go with it, shouldn't we document the change in the v18 release notes? Regards, -- Fujii Masao NTT DATA Japan Corporation
