> a lot of real world performance comes down to how efficiently you are calling external services (including the database)

Apart from that my experience over the last 20 years was that a lot of performance is lost because of memory allocation (in GCed languages like Java or JavaScript). Removing allocation in hot loops really goes a long way and leads to 10 or 100 fold runtime improvements.

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kykat 2 hours ago | parent | next [-]

This has been the key for me as well, memory allocation in hot paths is usually the first optimization that I look for. It's quite surprising to see how far very inefficient algorithms (time complexity wise) can go as long as no allocations are made.

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gmueckl 2 hours ago | parent | prev [-]

This applies to non-GC languages as well. Memory management is slow. Even with manual memory management I have been able to dramatically speed up code simply by modifying how memory is allocated.

Parts of the GC language crowd in particular have come to hold some false optimistic beliefs about how well a GC can handle allocations. Also, Java and C# can sneak in silly heap allocations in the wrong places (e.g. autoboxing). So there is a tendency for programs to overload the GC with avoidable work.

	▲	mrsmrtss an hour ago \| parent [-]
		Autoboxing is more a Java problem mainly because of type erasure with generics. C# has "proper" generics and no hidden boxing is occuring there.