Quick answer
A memory leak occurs when an application allocates memory and does not release it after use. It is recognized by constant growth in memory consumption and slowdown. It is detected with memory monitoring tools and code analysis, and resolved by removing the cause, most often forgotten references.
How to recognize the problem
- Application memory consumption constantly grows during runtime
- Application slows down over time and becomes unstable
- Program crashes with an out-of-memory error
- Operating system starts using swap and stutters
Most common causes
Forgotten references
Objects remain in memory because a reference still points to them, even though they are no longer needed. This is the most common cause of leaks.
Unremoved event listeners
Listeners and callback functions that are added without being removed keep objects in memory. This is especially common in long-running applications.
Unbounded caches
A cache that grows without a limit or without entry expiration will eventually consume all available memory. The same applies to global collections.
Reference cycles
Objects that reference each other can remain in memory if the garbage collector cannot clean them up. In languages and environments that use reference counting, cycles are a common cause of leaks.
Step-by-step fix
- 1
Confirm that it is a leak
Start the application and monitor memory consumption through Task Manager (Windows) or Activity Monitor (macOS). If memory grows over time and does not drop after operations complete, it is likely a leak. Note the initial value and repeat the same action multiple times.
- 2
Isolate the scenario that causes growth
Repeat one functionality at a time (opening screens, loading data, sending requests) and observe memory. The goal is to find the smallest sequence of steps that causes constant growth. Write down the steps so you can reproduce them later.
- 3
Use a memory monitoring tool
In a browser, open DevTools > Memory and take a heap snapshot before and after the suspicious action. Compare the snapshots and look for objects that remain. In Node.js use
node --inspectand Chrome DevTools, and in .NET use Visual Studio Diagnostic Tools. - 4
Analyze the heap snapshot
In the tool, review the list of objects sorted by size or number of instances. Pay attention to objects that should have been removed. Follow the reference chains (retainers) to see what keeps the object in memory.
- 5
Check event listeners and timers
Search the code for places where you add listeners (
addEventListener,on,subscribe) and check whether you remove them (removeEventListener,off,unsubscribe). The same applies tosetIntervalandsetTimeout, which should be stopped usingclearIntervalandclearTimeoutwhen no longer needed. - 6
Limit caches and collections
For caches, use a size limit or expiration time (e.g., LRU cache). Avoid global arrays and maps that grow uncontrollably. Regularly clean old entries.
- 7
Remove the cause and test
After you find the cause, modify the code so that references are released. Repeat the same test and monitor memory: it should remain stable. If necessary, add an automated test that checks that memory does not grow.
If nothing helps
If you cannot find the cause, consider simplifying the part of the code you suspect and testing again. Sometimes the leak comes from a third-party library; check whether it is updated and whether the problem is known. In production, monitor memory through monitoring tools and set an alarm when consumption exceeds a threshold. For complex cases, use advanced tools such as heap profiler and allocation analysis tools. If the leak occurs only under load, test with a simulation of multiple users.
How to prevent it
- Regularly review code for places where listeners and timers are added
- Use bounded caches and clean collections
- Test memory before releasing to production
- Monitor memory consumption in production
When to call a professional
If the leak causes crashes in production or you cannot reproduce it, contact IT support or a more experienced developer for analysis.
Software and product development · Custom apps, SaaS and an MVP in 4 to 8 weeksFAQ
How do I know if the application is leaking memory or is just demanding?
If memory grows constantly during runtime and is not released after operations complete, it is likely a leak. A demanding application may use more memory, but it should release it when no longer needed.
Is a memory leak dangerous for security?
It can be. A leak can lead to resource exhaustion and system crash, which attackers can exploit for denial of service (DoS). Also, memory containing sensitive data may remain available longer, increasing the risk of information leakage.
How often should memory be checked?
It is recommended to check with every major change and regularly in production. Automated tests can help detect leaks early.