maxoldspacesize

MaxOldSpaceSize, commonly exposed as the command line flag --max-old-space-size, is a parameter used with the V8 JavaScript engine to control the maximum size of the old generation heap. It is used in environments that run V8-based runtimes, such as Node.js and Chromium-based applications.

In V8, the heap is divided into generations: a new space (young generation) for short-lived objects and an old space (tenured generation) for longer-lived objects. The max-old-space-size setting specifies the upper limit of memory that can be allocated for the old space. Increasing this limit allows larger or longer-running applications to store more data in memory, but it also affects overall memory usage and garbage collection behavior.

Usage and examples: to run a Node.js application with a larger memory ceiling, you can start the process as node --max-old-space-size=4096 app.js, which requests up to 4 gigabytes for the old space. The value is expressed in megabytes. If the limit is reached, the runtime will trigger garbage collection or throw an out-of-memory error depending on the situation.

Impact and considerations: raising max-old-space-size can reduce the frequency of full-heap garbage collections for memory-intensive workloads, potentially improving throughput. However, it increases the total memory footprint of the process and can lead to longer pause times during garbage collection. It may also be constrained by the operating system and hardware, particularly on 32-bit architectures or systems with limited physical memory.

Related options: there are additional flags to influence heap sizing, such as --initial-old-space-size to set the starting size, and other flags that affect memory management. Settings should be tested under realistic workloads to balance memory usage and performance.