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Sunday, June 04, 2006

So I Was Bored and...

...looking through articles on lock-free data structures. Amusingly, one that looked interesting was by the author of Hoard - Quantifying the Performance of Garbage Collection vs. Explicit Memory Management. I didn't actually read the whole thing, but the conclusions were rather striking:
Comparing runtime, space consumption, and virtual memory footprints over a range of benchmarks, we show that the runtime performance of the best-performing garbage collector is competitive with explicit memory management when given enough memory. In particular, when garbage collection has five times as much memory as required, its runtime performance matches or slightly exceeds that of explicit memory management. However, garbage collection’s performance degrades substantially when it must use smaller heaps. With three times as much memory, it runs 17% slower on average, and with twice as much memory, it runs 70% slower. Garbage collection also is more susceptible to paging when physical memory is scarce. In such conditions, all of the garbage collectors we examine here suffer order-of-magnitude performance penalties relative to explicit memory management.

So, garbage collection doesn't sound so good for practical applications. Interestingly, this apparently debunks my belief that garbage collection was the optimal memory allocation strategy to use for embedded systems that are very tight on memory. Well, maybe, maybe not. I was thinking in terms of memory usage. Garbage collection allows blocks to be relocated in memory, allowing new allocations of arbitrary size to get around fragmentation problems (assuming there's enough free memory, period). But this report shows that doing so would come at a hefty performance cost, which may or may not be tolerable.

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