In the Spark UI, GC (Garbage Collection) time refers to the amount of time spent by the JVM (Java Virtual Machine) cleaning up and freeing up memory that is no longer being used.
When a Spark application runs, it creates a large number of objects in memory. These objects take up memory, but they may no longer be needed once the application has completed a certain task. The JVM’s Garbage Collector (GC) is responsible for identifying and freeing up these unused objects, so that the memory can be used for other purposes.
The GC time is the amount of time spent by the JVM in performing this cleanup process. The GC time is displayed in the Spark UI as a metric, typically in milliseconds. It can be found under the “Task Metrics” tab, in the “GC Time” section.
The GC time is an important metric to monitor, as it can indicate the performance of the JVM and the efficiency of the GC algorithm. A high GC time may indicate that the GC is not working efficiently, and is spending too much time cleaning up memory. This can lead to performance issues, such as longer task completion times. A high GC time can be caused by a number of factors, such as:
- High heap usage: If the heap usage is high, the GC will have more work to do, which can increase the GC time.
- Poor GC tuning: The GC algorithm can be configured through various parameters, if these parameters are not set correctly, it can lead to a high GC time.
- High object creation rate: If the application is creating a large number of objects, the GC will have more work to do, which can increase the GC time.
It’s good practice to monitor the GC time of a Spark application, and take steps to reduce it if it becomes too high. This can include tuning the GC algorithm, reducing the heap size, and reducing the object creation rate.
In summary, GC time in Spark UI is the amount of time spent by the JVM cleaning up and freeing up memory that is no longer being used. It’s an important metric to monitor as it can indicate the performance of the JVM and the efficiency of the GC algorithm, and can be caused by high heap usage, poor GC tuning and high object creation rate.
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