[The manual for Postgres 12 says][1]:
> The following operations are always parallel restricted.
> - Scans of common table expressions (CTEs).
> - Scans of temporary tables.
> - ...
Further down on the same [manual page:][2]
> [...] Similarly, functions must be marked PARALLEL RESTRICTED if they access
> temporary tables, client connection state, cursors, prepared
> statements, or miscellaneous backend-local state which the system
> cannot synchronize across workers. For example, setseed and random are
> parallel restricted for this last reason.
[1]: https://www.postgresql.org/docs/12/parallel-safety.html
That means that these CTEs can only be scanned in the
leader process.
> The following operations are always parallel restricted.
> - Scans of common table expressions (CTEs).
> - Scans of temporary tables.
> - ...
Further down on the same [manual page:][2]
> [...] Similarly, functions must be marked PARALLEL RESTRICTED if they access
> temporary tables, client connection state, cursors, prepared
> statements, or miscellaneous backend-local state which the system
> cannot synchronize across workers. For example, setseed and random are
> parallel restricted for this last reason.
No mention of CTEs.
I searched the list archives and found a statement from Thomas Munro [here][3]:
> That means that these CTEs can only be scanned in the leader process.
Now I am unsure whether I can use `PARALLEL SAFE` for functions containing a CTE (while fulfilling all other criteria)?
Would the new inlining of CTEs in Postgres 12 have any role in this?
I posted a [similar question on dba.SE][4].
Regards
Erwin Brandstetter
That means that these CTEs can only be scanned in the
leader process.
