ATTACH/DETACH partitions and locking

Hello,

According to patch[1] and after playing with v12 beta1 I think that this 
item can be dropped from "5.11.3. Implementation Using Inheritance" 
section of v12 docs:

"Some operations require a stronger lock when using declarative 
partitioning than when using table inheritance. For example, adding or 
removing a partition to or from a partitioned table requires taking an 
ACCESS EXCLUSIVE lock on the parent table, whereas a SHARE UPDATE 
EXCLUSIVE lock is enough in the case of regular inheritance."

Small patch attached.


[1] ATTACH/DETACH PARTITION CONCURRENTLY
https://www.postgresql.org/message-id/flat/CAKJS1f9QjUwQrio20Pi=yCHmnouf4z3SfN8sqXaAcwREG6k0zQ@mail.gmail.com

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Pavel Luzanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company