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The Java Mission Control tool in the JDK provides statistics about object allocation in new TLAB and allocations outside TLAB. (It's under Memory/Allocations). What is the significance of these statistics, what is good for the performance of an application? Should I be worried if some objects are allocated outside TLAB and if yes, what can I do about it?
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Small objects in Java are allocated in a TLAB (Thread Local Area Buffer). TLAB is a small memory area where new objects are allocated. Once a TLAB is full, the thread gets a new one. Logging all memory allocations gives an overhead; therefore, all allocations that triggered a new TLAB are logged.
TLAB stands for Thread Local Allocation Buffer and it is a region inside Eden, which is exclusively assigned to a thread. In other words, only a single thread can allocate new objects in this area. Each thread has own TLAB.
A TLAB is a Thread Local Allocation Buffer. The normal way objects are allocated in HotSpot is within a TLAB. TLAB allocations can be done without synchronization with other threads, since the Allocation Buffer is Thread Local, synchronization is only needed when a new TLAB is fetched.
So, the ideal scenario is that as much as possible of the allocations are done in TLABs.
Some objects will be allocated outside TLABs, for example large objects. This is nothing to worry about as long as the percentage of allocations outside TLABs vs allocations in new TLABs is low.
The TLABs are dynamically resized during the execution for each thread individually. So, if a thread allocates very much, the new TLABs that it gets from the heap will increase in size. If you want you can try to set the flag -XX:MinTLABSize to set minimum TLAB size, for example -XX:MinTLABSize=4k
Answer provided by my colleague David Lindholm :)
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