[BUGS] BUG #14675: Perfomance Issue after Upgrading from 9.5.3 to 9.6.3

The following bug has been logged on the website:

Bug reference:      14675
Logged by:          Martin Walpen
Email address:      walpino@gmx.ch
PostgreSQL version: 9.6.3
Operating system:   CentOS Linux release 7.3.1611
Description:

Hello 

we wanna upgrade our Installations from Version 9.5.3 to 9.6.3

everything works fine with the pg_upgrade

after the Upgrade process we encountered an performance issue 

we have a join in a select statement 

simply said, it looks like 


select....
from
where column_a = coalesce(col_b, coalesce(col_c, col_b))

this was fast on 9.5.3 
but now on 9.6.3 is is slow really really slow

the explain plan looks similar and not big difference


when I changed  this query to

select....
from
where column_a = coalesce(col_b, col_c, col_b)

which should be the same 


it was as fast as on 9.5.3

do you have any explanation for that?

thanks




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