51.2. How Connections are Established
is implemented using a
process per user
client/server model. In this model
there is one
. As we do not
know ahead of time how many connections will be made, we have to
that spawns a new
server process every time a connection is requested. This master
process is called
and listens at a
specified TCP/IP port for incoming connections. Whenever a request
for a connection is detected the
process spawns a new server process. The server tasks
communicate with each other using
to ensure data integrity
throughout concurrent data access.
The client process can be any program that understands the PostgreSQL protocol described in Chapter 53 . Many clients are based on the C-language library libpq , but several independent implementations of the protocol exist, such as the Java JDBC driver.
Once a connection is established the client process can send a query to the backend (server). The query is transmitted using plain text, i.e., there is no parsing done in the frontend (client). The server parses the query, creates an execution plan , executes the plan and returns the retrieved rows to the client by transmitting them over the established connection.