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Tip of the Day
Language: Java
Expertise: Advanced
Oct 21, 2016

Memory Tuning: Key Performance Indicators

When you are tuning the application's memory and garbage collection settings, you should take well-informed decisions based on the key performance indicators. But there is an overwhelming amount of metrics reported; which one to choose and which one to leave? This article intends to explain the right KPIs and right tools to source them.

What are the right KPIs?

  1. Throughput
  2. Latency
  3. Footprint

Throughput

This is the amount of time your application spends in processing customer transactions vs Garbage collection. Garbage Collection is a (necessary) over-head. As in business, one should always look for avenues to minimize the overhead. Let's study this through an example:

Let's say your application runs for 60 minutes. In this 60 minutes let's say 2 minutes is spent on GC activities.

It means application has spent 3.33% on GC activities (i.e. 2 / 60)

It means application throughput is 96.67% (i.e. 100 – 3.33). Now the question is: What is the acceptable throughput %? It depends on the application and business demands. Typically, one should target for more than 95% throughput.

Latency

This is the amount of time taken by one single Garbage collection event to run. This indicator should be studied from three fronts.

  1. Average GC time: What is the average amount of time spent on GC?
  2. Maximum GC time: What is the maximum amount of time spent on a single GC event? Your application may have service level agreements such as "no transaction can run beyond 10 seconds". In such cases, your maximum GC pause time can't be running for 10 seconds. Because during GC pauses, entire JVM freezes — no customer transactions will be processed. So it's important to understand the maximum GC pause time.
  3. GC Time Distribution: You should also understand how many GC events are completing with in what time range (i.e. within 0 - 1 second, 200 GC events are completed, between 1 - 2 second 10 GC events are completed)

Footprint

Footprint is basically the amount CPU consumed. Based on your GC algorithm, based on your memory settings, CPU consumption will vary. Some GC algorithms will consume more CPU (like Parallel, CMS), whereas other algorithms such as Serial will consume less CPU.

According to memory tuning Gurus, you can pick only 2 of them at a time.

  • If you want high throughput and low latency, then footprint will increase.
  • If you want high throughput and low footprint, then latency will increase.
  • If you want low latency and low footprint, then throughput will degrade.

The Right Tools

Throughput and Latency can be obtained from analyzing garbage collection logs. Upload your application's garbage collection log file in http://gceasy.io/ tool. This tool can parse garbage collection logs and generates Throughput and Latency indicators for you. Below is the screen shot from the http://gceasy.io/ tool showing the throughput and latency:

Ram Lakshmanan
 
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