clojure-dev 2026-07-06

With the PAM/PHM change in 1.13, would you expect any observable change in memory or CPU usage? (just curiousโ€”we rolled most of our apps on one server onto 1.13 Alpha 2, and we plan to observe them for 24 hours)

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Alex Miller (Clojure team) 2026-07-06T19:43:05.068559Z

more PAM, so likely slighly reduced memory but given that most maps are small, doubt it makes a ton of difference.

Alex Miller (Clojure team) 2026-07-06T19:44:16.315759Z

if you see anything, let us know

I'll see how the JVMs compare across all our servers tomorrow, when it's been running for 24 hours. Based on the 5 hours since I deployed it, it does look like reduced memory usage but it's probably a bit too early to call it.

An apples-to-apples comparison shows no noticeable change in memory usage, between 1.12.5 and 1.13.0 Alpha 2, after that deploy/restart about 24 hours ago. Sorry for the earlier false report ๐Ÿ˜ž

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After 24 hours, I am seeing lower heap, specifically lower old gen usage. But that may be just due to how long the same process has been running on the other servers. I feel comfortable pushing this onto our other servers tho', at this point...

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Alex Miller (Clojure team) 2026-07-07T19:50:22.971369Z

lower old gen would make sense to me wrt fewer PHMs (which can live for a long time via structural sharing)

Would you expect as much as 50MB lower? (200MB -> 150MB) I should have restarted at least one of the other servers' processes at the same time for a true comparison ๐Ÿ˜ž

Pushed 1.13 Alpha 2 to another server, and also restarted the 1.12.5 app on yet another server. I'll get a true apples-to-apples comparison tomorrow!

Alex Miller (Clojure team) 2026-07-07T19:55:17.571689Z

I don't have an expectation - will totally depend on usage