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Comment by eva1984 | Hacker News Reader

eva1984

Who said microservices don't need large heaps? The prefix 'micro' means the share of responsibility and boundary of functionality, not any hints at memory size.

Of cause JVM needs to focus on large heaps. Now it still stucks somewhere at 32GB for performance reason. And for heavy-lifting application like HBase/ElasticSearch, that is currently OK, but still makes it quite inconvenient to utilize larger memory(you might need deploy multiple instances on the same box, etc).

You can't invent a new buzzword and tell other people they are solving the wrong problem.

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> Now it still stucks somewhere at 32GB for performance reason

Short version: No it's not.

Long version: Heap is under 30 GB or over 40 GB. Never between. There is a JVM optimization that allows it to use 4 byte pointers up to 30GB of heap.

What is the reasoning for this? I think JVM still has problem handling real large heaps, the GC stop will be unbearable..Does thing change recently?

There is no problem to handle large heaps.

There is simply a gap: A 30 GB heap (with 4 bytes pointers) may be similar in capacity to a 40 GB heap (with 8 bytes pointers).

Guides and documentation (elastisearch) are simplifying this as "java can't do more than 30 GB heap", which is factually incorrect. You can do a 60GB if you want.

> There is no problem to handle large heaps.

That's not true, dealing with large heaps is problematic in any garbage collected language because due to fragmentation you end up in stop-the-world full GC phases. Which for a big heap (i.e. bigger than 4 GB!), you can end up with latencies measured in seconds or even minutes.

The article mentions the CMS GC for Java, which has this problem. The G1 GC, introduced in Java 7 I think, is much better, however from what I've read it too isn't immune to full GCs. Of course for Java you also have the Azul "pauseless GC", which is supposed to never do this, but it is a commercial solution. And the article also mentioned another GC currently being contributed by Red Hat, which is good to hear.

Define large? I never had problem by increasing a heap from 10 to 20 GB.

Sure, if you go from 300MB to 30GB, the GC might behave differently and maybe some applications can't take it.

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