If you are using the format specified by PGP, then the algo used for encryption is stored in the header, and that of course will be used for decryption. Trying to manually specify a algo to use for decryption is pointless.
Here is a working example of encryption and decryption:
An update of that magnitude is inevitably going to take a substantial amount of time, no matter how good your configuration is or how powerful the hardware. It's possible there might be room for improvement, but there are not enough details to go on here. For a start, it would be interesting to know the output of:
EXPLAIN (VERBOSE, SETTINGS)
Yes, this is required. There is no concept of an index over all
partitions in PostgreSQL. The requirement of having the partition key
a subset of the primary key allows us to implement primary keys by
just having individual unique indexes on each partition.
There's mention in section 184.108.40.206. "Unique constraints on
partitioned tables must include all ...