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<font face="monospace">Hi Jonathan,<br>
<br>
Thanks for starting this discussion. This is a topic that I am
interested in as well.<br>
<br>
I think the general question is:<br>
<br>
"How do I use as much memory as possible for the JVM without
getting OOM-killed".<br>
<br>
Traditionally, the JVM automatically picks an Xmx that's about 1/4
of the total physical RAM on the host. This is OK for for plain
old servers or desktop environments that runs lots of processes.
However, in containers which typically have a very small number of
processes, such a default is too conservative.<br>
<br>
However, if you set the -Xmx too high, the total amount of memory
used by the JVM can be unpredictable, because there are
allocations inside and outside of the Java heap. Also, in your
case, you have other processes running inside the same container
that the JVM has no direct control upon.<br>
<br>
It makes sense for the JVM to dynamically adjust its size, but we
should think about different scenarios to see what our goals
should be<br>
<br>
- In the simplest case, you have a single JVM process running
inside the container. How do you balance its Java heap vs non-Java
heap usage?<br>
<br>
- If you have two JVM processes running inside the container, how
do they coordinate?<br>
<br>
- If the fluctuation is caused by other processes, can the JVM
react quickly (run GC and free up caches) to respond to quick
spikes? Do we need to configure the container to allow temporarily
over-budget (something like "you can be 100MB over budget for less
than 20ms") so the JVM has time to shrink itself?<br>
<br>
- Conversely, how can a spiky process request the JVM to
temporarily give up some memory?<br>
<br>
It seems to me that for the more complex scenarios, it's not
enough for each individual JVM to make decisions on its own. We
may need some sort of intra-process coordination.<br>
<br>
Thanks<br>
- Ioi<br>
<br>
</font><br>
<div class="moz-cite-prefix">On 9/13/2022 12:52 PM, Jonathan Joo
wrote:<br>
</div>
<blockquote type="cite" cite="mid:CACz-JM5S=gLk+RTZ-rVNNW7emM78riTPyU3JNrDXuNYkojAmRw@mail.gmail.com">
<div dir="ltr">
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Hello hotspot-dev and hotspot-gc-dev,</span></p>
<br>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">My name is Jonathan, and I'm working on the Java Platform Team at Google. Here, we are working on a project to address Java container memory issues, as we noticed that a significant number of Java servers hit container OOM issues due to people incorrectly tuning their heap size with respect to the container size. Because our containers have other RAM consumers which fluctuate over time, it is often difficult to determine a priori what is an appropriate Xmx to set for a particular server. </span></p>
<br>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">We set about trying to solve this by dynamically adjusting the Java heap/gc behavior based on the container usage information that we pass into the JVM. We have seen promising results so far, reducing container OOMs by a significant amount, and oftentimes also reducing average heap usage (with the tradeoff of more CPU time spent doing GC). </span></p>
<br>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Below (under the dotted line) is a more detailed explanation of our initial approach. Does this sound like something that may be useful for the general OpenJDK community? If so, would some of you be open to further discussion? I would also like to better understand what container environments look like outside of Google, to see how we could modify our approach for the more general case.</span></p>
<br>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Thank you!</span></p>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="background-color:transparent;font-size:11pt;white-space:pre-wrap;color:rgb(0,0,0);font-family:Arial">
</span></p>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="background-color:transparent;font-size:11pt;white-space:pre-wrap;color:rgb(0,0,0);font-family:Arial">Jonathan</span></p>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">------------------------------------------------------------------------</span></h3>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Introduction:</span></h3>
<p dir="ltr" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Adaptable Heap Sizing (AHS) is a project internal to Google that is meant to simplify configuration and improve the stability of applications in container environments. The key is that in a containerized environment, we have access to container usage and limit information. This can be used as a signal to modify Java heap behavior, helping prevent container OOMs.</span></p>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Problem:</span></h3>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Containers at Google must be properly sized to not only the JVM heap, but other memory consumers as well. These consumers include non-heap Java (e.g. native code allocations), and simultaneously running non-Java processes. </span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Common antipattern we see here at Google: </span></p></li>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">We have an application running into container OOMs. </span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">An engineer raises both container memory limit and Xmx by the same amount, since there appears to be insufficient memory.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">The application has reduced container OOMs, but is still prone to them, since G1 continues to use most of Xmx.</span></p></li>
</ul>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">This results in many jobs being configured with much more RAM than they need, but still running into container OOM issues.</span></p></li>
</ul>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Hypothesis:</span></h3>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">For preventing container OOM: Why can't heap expansions be bounded by the remaining free space in the container?</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">For preventing the `unnecessarily high Xmx` antipattern: Why can't target heap size be set based on GC CPU overhead?</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">From our work on Adaptable Heap Sizing, it appears they can!</span></p></li>
</ul>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Design:</span></h3>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">We add two manageable flags in the JVM</span></p></li>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Current maximum heap expansion size</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Current target heap size</span></p></li>
</ul>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">A separate thread runs alongside the JVM, querying:</span></p></li>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Container memory usage/limits</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">GC CPU overhead metrics from the JVM.</span></p></li>
</ul>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">This thread then uses this information to calculate new values for the two new JVM flags, and continually updates them at runtime.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">The `Current maximum heap expansion size` informs the JVM what is the maximum amount we can expand the heap by, while staying within container limits. This is a hard limit, and trying to expand more than this amount results in behavior equivalent to hitting the Xmx limit.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">The `Current target heap size` is a soft target value, which is used </span><span style="font-size:10.5pt;font-family:Roboto,sans-serif;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">to resize the heap (when possible) so as to bring GC CPU overhead toward its target value.</span><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline"> </span></p></li>
</ul>
<br>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">Results:</span></h3>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">At Google, we have found that this design works incredibly well in our initial rollout, even for large and complex workloads.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">After deploying this to dozens of applications:</span></p></li>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Significant memory savings for previously misconfigured jobs (many of which reduced their heap usage by 50% or more)</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Significantly reduced occurrences of container OOM (100% reduction in vast majority of cases)</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">No correctness issues</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">No latency regressions*</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">We plan to deploy AHS across a much wider subset of applications by EOY '22.</span></p></li>
</ul>
</ul>
<br>
<h3 dir="ltr" style="line-height:1.38;margin-top:16pt;margin-bottom:4pt"><span style="font-size:14pt;font-family:Arial;color:rgb(67,67,67);background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap">*Caveats: </span></h3>
<ul style="margin-top:0px;margin-bottom:0px">
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><h3 dir="ltr" role="presentation" style="line-height:1.38;margin-top:16pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-weight:400;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Enabling this feature might require tuning of the newly introduced default GC CPU overhead target to avoid regressions.</span></h3></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Time spent doing GC for an application may increase significantly (though generally we've seen in practice that even if this is the case, end-to-end latency does not increase a noticeable amount)</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:10.5pt;font-family:Roboto,sans-serif;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">Enabling AHS results in frequent heap resizings, but we have not seen evidence of any negative effects as a result of these more frequent heap resizings.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">AHS is not necessarily a replacement for proper JVM tuning, but should generally work better than an untuned or improperly tuned configuration.</span></p></li>
<li dir="ltr" style="margin-left:15px;list-style-type:disc;font-size:11pt;font-family:Arial;color:rgb(0,0,0);background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline;white-space:pre-wrap"><p dir="ltr" role="presentation" style="line-height:1.38;margin-top:0pt;margin-bottom:0pt"><span style="font-size:11pt;background-color:transparent;font-variant-numeric:normal;font-variant-east-asian:normal;vertical-align:baseline">AHS is not intended for every possible workload, and there could be pathological cases where AHS results in worse behavior.</span></p></li>
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