Re: ERROR: cannot start subtransactions during a parallel operation

On 06/29/2018 04:00 PM, Mai Peng wrote:
> Hello,
>
> On a pG10.4 instance, my query ( a simple select from a view) throw this
> error:
> ERROR:  cannot start subtransactions during a parallel operation
> CONTEXT:  PL/pgSQL function check_validity(ltree[]) line 4 during
> statement block entry
>

So, what does this check_validity function do? It's not part of
PostgreSQL, and it apparently tries to do something that opens a
subtransation. Like a SAVEPOINT for example ...

> But prefixing this query by "set max_parallel_workers_gather=0" make it
> works.
>
> When I take off the column that is checked by a function, no need to add
> set max_parallel_workers_gather=0 .
>

Well, that's not really surprising - if you disable parallelism the
query is no longer subject to the restriction about subtransactions.

> How could I continue to use the default max_parallel_workers_gather (2).
>

Modity the function not to start a subtransaction.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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