# Interpret GC log messages - which value is pre and which is post?

**URL:** <https://discuss.elastic.co/t/interpret-gc-log-messages-which-value-is-pre-and-which-is-post/33105>\
**Category:** Elasticsearch\
**Created:** [October 27, 2015, 8:23pm UTC](https://discuss.elastic.co/t/interpret-gc-log-messages-which-value-is-pre-and-which-is-post/33105 "2015-10-27T20:23:43Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Nikita\_Tovstoles](https://avatars.discourse-cdn.com/v4/letter/n/f17d59/32.png) [@Nikita\_Tovstoles](https://discuss.elastic.co/u/Nikita_Tovstoles)\
**Post date:** [October 27, 2015, 8:23pm UTC](https://discuss.elastic.co/t/interpret-gc-log-messages-which-value-is-pre-and-which-is-post/33105/1 "2015-10-27T20:23:43Z")

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I see messages like below in ES server 1.7.1 log:

> [2015-10-27 12:20:07,669][INFO][monitor.jvm] [my\_host] [gc][young][67][20] duration [721ms], collections [1]/[1.7s], total [721ms]/[4s], memory [285.6mb]-\>[291.8mb]/[1.9gb], all\_pools {[young] [27mb]-\>[280.4kb]/[66.5mb]}{[survivor] [8.3mb]-\>[8.3mb]/[8.3mb]}{[old] [250.2mb]-\>[283.2mb]/[1.9gb]}

Let's take the `old` gen: `{[old] [250.2mb]->[283.2mb]/[1.9gb]}` or $A -\> $B / $C

is $A = value post-gc, $B = value pre-gc and $C = capacity? Or did heap allocation really grow as result of GC?

Thanks,

-nikita

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**Author:** ![Nikita\_Tovstoles](https://avatars.discourse-cdn.com/v4/letter/n/f17d59/32.png) [@Nikita\_Tovstoles](https://discuss.elastic.co/u/Nikita_Tovstoles)\
**Post date:** [October 27, 2015, 8:29pm UTC](https://discuss.elastic.co/t/interpret-gc-log-messages-which-value-is-pre-and-which-is-post/33105/2 "2015-10-27T20:29:16Z")

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answering own question (after getting a cup of coffee): format is $pre -\> $post / $capacity. In the above example some objects were likely promoted from young to tenured (old) gen, thus the latter did indeed increase post-GC

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [July 5, 2017, 11:42pm UTC](https://discuss.elastic.co/t/interpret-gc-log-messages-which-value-is-pre-and-which-is-post/33105/3 "2017-07-05T23:42:19Z")

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