Creating a Connection Pool

From a clojure.java.jdbc spec

You can create a C3P0 connection pool with any clojure.java.jdbc connection spec map with :subname and :subprotocol keys. connection-pool-spec will return a clojure.java.jdbc connection spec you can use directly:

(require '[clojure.java.jdbc :as jdbc]
         '[metabase.connection-pool :as connection-pool])

;;; Create a C3P0 connection pool

(let [pool-spec (connection-pool/connection-pool-spec my-jdbc-spec)]
  (jdbc/query pool-spec ["SELECT *"]))

(You will almost certainly want to store your pool somewhere, such as in an atom).

From a JDBC URL String:

You can create a pooled DataSource (e.g., for use with next-jdbc) by calling pooled-data-source-from-url:

(require '[next.jdbc :as jdbc]
         '[metabase.connection-pool :as connection-pool])

(with-open [connection (jdbc/get-connection (connection-pool/pooled-data-source-from-url "jdbc:postgresql:localhost:3000/my_db"))]
  (reduce my-fn init-value (jdbc/plan connection ["SELECT *"])))

Configuring the connection pool

You can set connection pool options such as size in a c3p0.properties file, or by passing them as a map to connection-pool-spec:

(def ^:private connection-pool-properties
  {"maxIdleTime"     (* 3 60 60)
   "minPoolSize"     1
   "initialPoolSize" 1
   "maxPoolSize"     15})

(def my-pool-spec
  (connection-pool/connection-pool-spec my-jdbc-spec connection-pool-properties))

See https://www.mchange.com/projects/c3p0/#configuration_properties for a list of all options.

Destroying connection pools

destroy-connection-pool! will destroy the connection pool you created:

(connection-pool/destroy-connection-pool! pool-spec)

Legal Stuff

Copyright © 2019 Metabase, Inc. This project is licensed under the Eclipse Public License, same as Clojure.