git clone ''

(ql:quickload :clojure-goes-fast.clj-memory-meter)


This library is a thin wrapper around Java Agent for Memory Measurements. It allows to inspect at runtime how much memory an object occupies together with all its child fields.

Extra features compared to jamm:

  1. Easy runtime loading (you can start using it at any time at the REPL, providing additional startup parameters is not necessary).
  2. Human-readable size output.

jamm JAR file is shipped together with clj-memory-meter and unpacked at runtime.


JDK9+: you must start the JVM with option -Djdk.attach.allowAttachSelf, otherwise the agent will not be able to dynamically attach to the running process. For Leiningen, add :jvm-opts ["-Djdk.attach.allowAttachSelf"] to project.clj. For Boot, start the process with environment variable BOOT_JVM_OPTIONS="-Djdk.attach.allowAttachSelf".

Add com.clojure-goes-fast/clj-memory-meter to your dependencies:

Once loaded, you can measure objects like this:

(require '[clj-memory-meter.core :as mm])

;; measure calculates total memory occupancy of the object

(mm/measure "Hello, world!")
;=> "72 B"

(mm/measure [])
;=> "240 B"

(mm/measure (into {} (map #(vector % (str %)) (range 100))))
;=> "9.6 KB"

;; :shallow true calculates only memory occupied by the object itself,
;; without children

(mm/measure (object-array (repeatedly 100 #(String. "hello"))) :shallow true)
;=> "416 B"
(mm/measure (object-array (repeatedly 100 #(String. "hello"))))
;=> "2.8 KB"

;; :bytes true can be passed to return the raw number of bytes

(mm/measure (object-array (repeatedly 100 #(String. "hello"))) :bytes true)
;=> 2848

;; :debug true can be passed to print the object hierarchy. You can also pass an
;; integer number to limit the number of nested levels printed.

(mm/measure (apply list (range 4)) :debug true)

; root [clojure.lang.PersistentList] 256 bytes (40 bytes)
;   |
;   +--_first [java.lang.Long] 24 bytes (24 bytes)
;   |
;   +--_rest [clojure.lang.PersistentList] 192 bytes (40 bytes)
;     |
;     +--_first [java.lang.Long] 24 bytes (24 bytes)
;     |
;     +--_rest [clojure.lang.PersistentList] 128 bytes (40 bytes)
;       |
;       +--_first [java.lang.Long] 24 bytes (24 bytes)
;       |
;       +--_rest [clojure.lang.PersistentList] 64 bytes (40 bytes)
;         |
;         +--_first [java.lang.Long] 24 bytes (24 bytes)

;; Custom MemoryMeter object can be passed. See what you can configure here:


jamm is distributed under Apache-2.0. See APACHE_PUBLIC_LICENSE file. The location of the original repository is

clj-memory-meter is distributed under the Eclipse Public License. See ECLIPSE_PUBLIC_LICENSE.

Copyright 2018 Alexander Yakushev