clj-memory-meter is a small library that allows you to inspect at runtime how much memory an object occupies together with all its child fields. It is a thin wrapper around Java Agent for Memory Measurements.
Extra features compared to jamm:
- Easy runtime loading (you can start using it at any time at the REPL, providing additional startup parameters is not necessary).
- Human-readable size output.
jamm JAR file is shipped together with clj-memory-meter and unpacked at runtime.
JDK11+: you must start your application with JVM 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 tools.deps, add the same
:jvm-opts
to deps.edn
or write -J-Djdk.attach.allowAttachSelf
explicitly
in your REPL command.
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:
;; https://github.com/jbellis/jamm/blob/master/src/org/github/jamm/MemoryMeter.java
Note on JDK17+: Starting with Java 17, JVM no longer allows accessing private fields of classes residing in external modules. This made clj-memory-meter unusable in most scenarios. To alleviate this, in version 0.2.0 and forward if run on Java 17+, clj-memory-meter utilizes Unsafe to get into such private fields. This works but, as any Unsafe usage, can potentially crash the application. Use at your own risk. Also, the Unsafe itself may go away in the future versions of Java.
jamm is distributed under Apache-2.0. See APACHE_PUBLIC_LICENSE file. The location of the original repository is https://github.com/jbellis/jamm.
clj-memory-meter is distributed under the Eclipse Public License. See ECLIPSE_PUBLIC_LICENSE.
Copyright 2018-2022 Alexander Yakushev