From a technical perspective, Prisma Client consists of three major components:

  • JavaScript client library
  • TypeScript type definitions
  • A query engine

All of these components are located in the generated .prisma/client folder after you ran prisma generate.

This page covers relevant technical details about the query engine.

The query engine file

The query engine file is different for each operating system. It is named query-engine-PLATFORM or libquery_engine-PLATFORM where PLATFORM corresponds to the name of a compile target. Query engine file extensions depend on the platform as well. As an example, if the query engine must run on a Darwin operating system such as macOS, it is called libquery_engine-darwin.dylib.node or query-engine-darwin. You can find an overview of all supported platforms here.

The query engine file is downloaded into the runtime directory of the generated Prisma Client when prisma generate is called.

Note that the query engine is implemented in Rust. The source code is located in the prisma-engines repository.

The query engine at runtime

By default, the Prisma Client loads the query engine as a Node-API library. You can alternatively configure Prisma to use the query engine compiled as an executable binary, which is run as a sidecar process alongside your application. The Node-API library approach is recommended since it reduces the communication overhead between the Prisma Client and the query engine.

Diagram showing the query engine and Node.js at runtime

The query engine is started when the first Prisma Client query is invoked or when the $connect() method is called on your PrismaClient instance. Once the query engine is started, it creates a connection pool and manages the physical connections to the database. From that point onwards, the Prisma Client is ready to send queries to the database (e.g. findUnique, findMany, create, ...).

The query engine is stopped and the database connections are closed when $disconnect() is invoked.

The following diagram depicts a "typical flow":

  1. $connect() is invoked on Prisma Client
  2. The query engine is started
  3. The query engine establishes connections to the database and creates connection pool
  4. Prisma Client is now ready to send queries to the database
  5. Prisma Client sends a findMany() query to the query engine
  6. The query engine translates the query into SQL and sends it to the database
  7. The query engine receives the SQL response from the database
  8. The query engine returns the result as plain old JavaScript objects to Prisma Client
  9. $disconnect() is invoked on Prisma Client
  10. The query engine closes the database connections
  11. The query engine is stopped

Typical flow of the query engine at run time

Responsibilities of the query engine

The query engine has the following responsibilities in an application that uses Prisma Client:

  • manage physical database connections in connection pool
  • receive incoming queries from the Prisma Client Node.js process
  • generate SQL queries
  • send SQL queries to the database
  • process responses from the database and send them back to Prisma Client

Debugging the query engine

You can access the logs of the query engine by setting the DEBUG environment variable to engine:

$export DEBUG="engine"

You can also get more visibility into the SQL queries that are generated by the query engine by setting the query log level in Prisma Client:

const prisma = new PrismaClient({
log: ['query'],
})

Learn more about Debugging and Logging.

Configuring the query engine

Defining the query engine type for Prisma Client

As described above the default query engine is a Node-API library that is loaded into Prisma Client, but there is also an alternative implementation as an executable binary that runs in its own process. You can configure the query engine type by providing the engineType property to the Prisma Client generator:

generator client {
provider = "prisma-client-js"
engineType = "binary"
}

Valid values for engineType are binary and library. You can also use the environment variable PRISMA_CLIENT_ENGINE_TYPE instead.

  • Until Prisma 3.x the default and only engine type available was binary, so there was no way to configure the engine type to be used by Prisma Client and Prisma CLI.
  • From versions 2.20.0 to 3.x the library engine type was available and used by default by activating the preview feature flag "nApi" or using the PRISMA_FORCE_NAPI=true environment variable.

Defining the query engine type for Prisma CLI

Prisma CLI also uses its own query engine for its own needs. You can configure it to use the binary version of the query engine by defining the environment variable PRISMA_CLI_QUERY_ENGINE_TYPE=binary.

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