Connection Pooling in Clojure

clojure jdbc
clojure sql
clojure c3p0
hikari connection pool
clojure postgres
clojure hikaricp
clojure jdbc exception
clojure jdbc sql server

I am unable to understand the use of pool-db and connection function in this connection pooling guide.

(defn- get-pool
    "Creates Database connection pool to be used in queries"
    [{:keys [host-port db-name username password]}]
    (let [pool (doto (ComboPooledDataSource.)
                   (.setDriverClass "com.mysql.cj.jdbc.Driver")
                   (.setJdbcUrl (str "jdbc:mysql://"
                                     "/" db-name))
                   (.setUser username)
                   (.setPassword password)
                   ;; expire excess connections after 30 minutes of inactivity:
                   (.setMaxIdleTimeExcessConnections (* 30 60))
                   ;; expire connections after 3 hours of inactivity:
                   (.setMaxIdleTime (* 3 60 60)))]
        {:datasource pool}))

(def pool-db (delay (get-pool db-spec)))

(defn connection [] @pool-db)

; usage in code
(jdbc/query (connection) ["Select SUM(1, 2, 3)"])

Why can't we simply do?

(def connection (get-pool db-spec))

; usage in code
(jdbc/query connection ["SELECT SUM(1, 2, 3)"])

The delay ensures that you create the connection pool the first time you try to use it, rather than when the namespace is loaded.

This is a good idea because your connection pool may fail to be created for any one of a number of reasons, and if it fails during namespace load you will get some odd behaviour - any defs after your failing connection pool creation will not be evaluated, for example.

In general, top level var definitions should be constructed so they cannot fail at runtime.

Bear in mind they may also be evaluated during the AOT compile process, as amalloy notes below.

How to reuse database connections, jdbc-c3p0. c3p0, a mature, highly concurrent JDBC Connection pooling library for clojure.jdbc. Install. To configure the Hikari connection pool, Let’s create a new file database.clj in the infra directory. > touch src/wheel/infra/database.clj Then define a mount state datasource to manage the life-cycle of the connection pool.

In your application, you want to create the pool just one time and reuse it. For this reason, delay is used to wrap the (get-pool db-spec) method so that this method will be invoked only the first time it is forced with deref/@ and will cache the pool return it in subsequent forcecalls

Connection Pooling in Clojure, This property controls whether Connections obtained from the pool are in read- only mode by default. :connection-timeout, No, 30000, This property controls the � jdbc/with-connection takes the commands you want to run in that connection as arguments, after the spec. You are running no commands in the context with-connection creates, and running everything outside it, where the db connection is not bound.

The difference is that in the delay version a pool will be created only if it is called (which might not be the case if everything was cached), but the non-delay version will instantiate a pool no matter what, i.e. always, even if a database connection is not used.

delay runs only if deref is called and does nothing otherwise.

bostonaholic/clojure.jdbc-c3p0: C3P0 Connection Pool , In the last blog post, we bootstrapped the Clojure project using Mount and To configure the Hikari connection pool, Let's create a new file� Since clojure.jdbc 0.4.0-beta1, packages like this is not the recommended way to setup the connection pool. It provides the basic setup. If you want more control and access to all options, consider using the dbcp directly as documented in

I would suggest you use an existing library to handle connection pooling, something like hikari-cp, which is highly configurable and works across many implements of SQL.

tomekw/hikari-cp: A Clojure wrapper to HikariCP JDBC , A pool (cache) of reusable connections is maintained meaning when users connect to the database they can reuse an existing connection. When� The basic idea is to add your chosen connection pooling library to your project, import the appropriate class(es), define a function that consumes a "database spec" and produces a map containing a :datasource key whose value is the constructed pooled DataSource object, then use that hash map in place of your bare db-spec variable. You are responsible for creating the pooled data source object and passing the map containing it into any functions that need a database connection.

Configuring Database Connection Pooling, Migration and Reloaded , I am in desparate need of a clojure.jdbc with a connection pool example. I have googled and the link to github example is broken. Please help. r/Clojure: Clojure is a dynamic programming language / Lisp that targets the Java Virtual Machine. You simple look up the connection pool you should use based on

Clojure: connection pooling with hikari-cp, For your info, I use Postgresql db. You can use a Clojure wrapper for HikariCP, a JDBC connection pool. The off-the-shelf component available in� c3p0, a mature, highly concurrent JDBC connection pooling library for clojure.jdbc. connection pool example, Connection pool. DataSource is the preferd way to connect to the database in production enviroments, and is usually used for� By default, each operation opens a connection and executes the SQL inside a transaction. You can also run multiple operations against the same connection, either within a transaction or via connection pooling, or just with a shared connection. You can read more about reusing connections on the Reusing Connections page.