50.2. How Connections Are Established

50.2. How Connections Are Established
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+ PostgreSQL is implemented using a + simple “process per user” client/server model. In this model + there is one client process connected to + exactly one server process. As we do not + know ahead of time how many connections will be made, we have to + use a master process that spawns a new + server process every time a connection is requested. This master + process is called postgres and listens at a + specified TCP/IP port for incoming connections. Whenever a request + for a connection is detected the postgres + process spawns a new server process. The server tasks + communicate with each other using semaphores and + shared memory to ensure data integrity + throughout concurrent data access. +

+ The client process can be any program that understands the + PostgreSQL protocol described in + Chapter 52. 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. +

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50.1. The Path of a Query	Home	50.3. The Parser Stage