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PostgreSQL query protocol

Postgres has two ways to send queries to the server:

  1. Simple queries
  2. Extended protocol (prepared statements)

PgDog can handle both methods and can extract sharding hints from both query text and separate parameter messages.

Simple queries

Simple queries contain everything the server needs to execute them, including query text and parameters:

SELECT * FROM "users" WHERE "id" = 1;

Extended protocol

Extended protocol separates the query text from parameters. This allows the client to send the query text once and execute it multiple times using different parameter values:

SELECT * FROM "users" WHERE "id" = $1;

Parameter values are substituted with numbered placeholders. Values are sent in a separate protocol message.