On Thu, Jun 7, 2018 at 4:23 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Frits Jalvingh <jal@etc.to> writes:
>> The "good" news is that this effect is apparently caused by something else.
>> I fired those statements through an IDE (IntelliJ) written in Java and
>> using jdbc. There seems to be something odd going on in there, because when
>> I paste the query in psql then the effect with and without explain looks
>> the same: 3 processes of which 2 "parallel workers" doing enormous amounts
>> of I/O at 50..90% CPU. I will try to find out what easter egg in either
>> that IDE or the JDBC driver causes this 8-/.
>
> Ah. Something about query parameterization, is my bet.
The symptoms match this other report I just diagnosed over here:
https://www.postgresql.org/message-id/CAEepm%3D3rvRBxD_g8RngT6nAtUuTdGskL0xdDK3WXroebLDRwgg%40mail.gmail.com
We only allow parallelism if you asked for all rows to be returned,
but these GUI tools ask for a limited number. This is probably an
unintended consequence of commit 691b8d59, but I'm not sure. Let's
discuss that over in that other thread.
--
Thomas Munro
http://www.enterprisedb.com