Can functions containing a CTE be PARALLEL SAFE? - Mailing list pgsql-general

From Erwin Brandstetter
Subject Can functions containing a CTE be PARALLEL SAFE?
Date
Msg-id CAGHENJ6jnwGBn5UG3ZjsTkOtvt1nRKuapcL9wx0Qx0H=HVvqxQ@mail.gmail.com
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Responses Re: Can functions containing a CTE be PARALLEL SAFE?
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[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.

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

  [1]: https://www.postgresql.org/docs/12/parallel-safety.html


 That means that these CTEs can only be scanned in the
leader process.

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