Is ZGC still in experimental?

Connaughton, Niall conniall at
Wed Nov 27 22:18:22 UTC 2019

Thanks, that helps clarify. For us running on an LTS release is preferred as we don't necessarily want to be in a position of needing to move to a newer JDK at high frequency. We're aware of ZGC being experimental and know we're somewhat wading into unknown waters, so it's a balance we have to think about between the potential benefits of a fundamentally different GC vs potential pitfalls or additional effort in keeping up to date. The Shenandoah team seem to be putting a lot of effort into backporting to earlier JDKs - I guess this is down to a choice they've specifically made.

On 11/27/19, 02:06, "Per Liden" <per.liden at> wrote:

    On 11/26/19 11:45 PM, Connaughton, Niall wrote:
    > I wanted to double check on this. Is the intention that ZGC in JDK 11 is not intended for production use and will never have backports to bring it up to a production ready level? Put another way - if we want to evaluate using ZGC for a production service, is it an effective pre-requisite to move to a later JDK than 11?
    > Obviously we can test with the JDK11 version, and if we don't happen to see any problems then can make an "at-your-own-risk" call on that. But the longer term plans for addressing issues will affect the appetite for whether to even start out on that version.
    Experimental status basically means it's a technical preview giving 
    people a chance to test it and provide feedback, without having to roll 
    their own JDK. We have backported bug fixes on a few occasions, but 
    that's typically only done if we think it's critical for one reason or 
    another, and the bar is high. We don't intend to make ZGC in 11 
    non-experimental. In the new JDK release model, LTS releases typically 
    don't get "new features" after GA.
    ZGC and the supporting infrastructure in Hotspot is moving along at a 
    fairly rapid pace, and quite a lot of good stuff has gone into each 
    release since 11. Using the latest JDK is always recommended if you're 
    using ZGC. ZGC in JDK 11 vs. 13 can for some workloads be a quite 
    noticeable leap, in terms of performance, latency, etc.
    Hope that helps.
    > Thanks,
    > Niall
    > On 10/31/19, 02:00, "zgc-dev on behalf of Per Liden" <zgc-dev-bounces at on behalf of per.liden at> wrote:
    >      I would way that's unlikely at this time, given ZGC's experimental
    >      status in 11.
    >      /Per
    >      On 10/30/19 8:28 PM, Sundara Mohan M wrote:
    >      > Hi Per
    >      >    Will these changes be merged back to JDK11 at any point?
    >      > For ex. uncommit memory feature or C2 related changes will be merged
    >      > back to 11?
    >      >
    >      > Thanks
    >      > Sundar
    >      >
    >      >
    >      > On Tue, Oct 22, 2019 at 11:04 AM Sundara Mohan M <m.sundar85 at
    >      > <mailto:m.sundar85 at>> wrote:
    >      >
    >      >     Ok, thanks for the update.
    >      >
    >      >     On Tue, Oct 22, 2019 at 1:12 AM Per Liden <per.liden at
    >      >     <mailto:per.liden at>> wrote:
    >      >
    >      >         Hi,
    >      >
    >      >         No decision has been made, but we're continuously evaluating
    >      >         where we
    >      >         stand. The new C2 load barriers (JDK-8230565) was a major milestone
    >      >         towards making ZGC rock solid. We can hopefully make it
    >      >         non-experimental
    >      >         sooner rather than later.
    >      >
    >      >         /Per
    >      >
    >      >         On 10/22/19 12:14 AM, Sundara Mohan M wrote:
    >      >          > Hi,
    >      >          >     Any idea when ZGC will be moved out of experimental flags?
    >      >          > Understand it is too early to move it out of experimental but
    >      >         do we have
    >      >          > any plan to run it without +UnlockExperimentalVMOptions?
    >      >          >
    >      >          > Thanks
    >      >          > Sundar
    >      >          >
    >      >

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