Postgresql - Currval Vs Session Pool

Hello, all.

In the PostgreSQL documentation I found "currval: Return the value most
recently obtained by nextval for this sequence in the current session ...."

In other documentations (pgpool, for example), I found "Connection Pooling
pgpool-II saves connections to the PostgreSQL servers, and reuse them
whenever a new connection with the same properties (i.e. username,
database, protocol version) comes in. It reduces connection overhead, and
improves system's overall throughput"

Then, I have the following question: PostgreSQL differentiates between
sessions created for the same user?

Background
==========
- I, traditionalmente, have several user in a web application (user table,
for example); but I use only one postgresql-db-user to get connetions to
database

- If a CREATE (CRUD) operation uses a head-detail couple of tables, then in
a transaction: data in HEAD table is inserted; next, the value for the
primary key is achieved from currval function; next references to head
table is inserted in detail table.

Other questions
===============
- If I use a "bd_user" user to get connections to PostgreSQL and I use
connetions Pool; if CONNECTION_01 and CONNECTION_02 concurrently try to
get value from "currval" function, what happens?

- Exist best practices to do what I trying.

Thank you, in advance.

------------------------
Gustavo Amarilla