The first answer: test & measure. Benchmark your code, use a JVM profiler to find hotspots, etc. Test every change you make to see if it has a measurable improvement. Any assumptions about what “should” be faster/slower are likely to be wrong.
The long answer: The JVM does not give you much control over how objects are arranged in memory. In Java and Clojure, almost everything is a pointer to an object on the heap. Java collection classes and Clojure collections store pointers to objects; they do not store values “in-line” like an array of structs in C. The JVM *may* have optimizations that try to arrange objects “near” other objects, but you have no control over this. So my (untested) expectation is that all Clojure collection types are more-or-less equal in terms of memory locality. The only built-in data structure that offers the possibility of contiguous allocation in Java — without dropping down to native code — is an array of primitives, such as integers or doubles. Clojure has built-in functions to create and manipulate Java primitive arrays, if that works for your use case. –S On Wednesday, April 20, 2016 at 2:03:10 PM UTC-4, JvJ wrote: > > I'm writing some code that I would like to perform as quickly as possible. > Currently, I am iterating over large hash maps and performing assocs and > dissocs. > > I don't know much about performance optimization, but I am told that > memory locality is a big factor. I would like to know how Persistent Maps, > Persistent Vectors, Transient Maps, and Transient Vectors compare to one > another in this respect. > > Also, the objects in the collection that I'm iterating over will > themselves be maps. So, if I had a vector with good memory locality, but > it stored what are effectively pointers to maps allocated elsewhere, will > that nullify the benefits of memory locality? > > Thanks > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
