Jonathan Scher <js@oxado.com> writes:
> CLUSTER uses an ACCESS EXCLUSIVE lock. Why does it forbid concurrent reads?

Because when it drops the old copy of the table there had better not be
any concurrent readers.

regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match