Groupcache: an alternative to memcached, written in Go

Re:Groupcache: an alternative to memcached, written in Go by twotwotwo on Tuesday July 30, 2013 @02:35AM (#6125630)

In any GC'd language, the less you allocate the less you GC, so "recycling" old objects when you need new ones can help. So where you'd normally make() a []byte, you can instead get one from a list or buffered channel you made of old discarded []bytes. So that gets you back to malloc/free/new/delete, but you can at least do it only for the most performance-relevant allocations in your program and keep being lazy everywhere else.

Another sometimes-useful way to save allocations--not for a cache, but in general--is just to turn short-lived allocations into longer-lived ones: if fooBuf is used and thrown away by each of several calls to obj.baz(), then make a single fooBuf and store it as a (private) field on obj, assuming that doesn't present thread-safety or other problems in the specific context.

There are certainly things you wouldn't use Go for, but now you know more about reducing memory pressure in GC'd languages. :)

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Re:Groupcache: an alternative to memcached, written in Go by chetanahuja on Tuesday July 30, 2013 @04:01AM (#6125814)

Well various techniques to recycle/reuse allocations instead of "garbaging" are well known techniques from the Java world too. Also, the generational collectors popular in the JVM's also do a good job of lots of short-lived allocations (as long as a vast majority of them die young).

The problem is, none of those things help when you have a large cache of small(ish) objects that need to be scanned fully at every GC cycle. There's nothing worse for your performance than stopping the world for a few seconds and using that time to wipe your L1/2/3 caches with completely useless data. That's the reason I called large-heaped caches the anti-pattern for a GC'd system.

Brad's answer about using large byte array allocations (and presumably, managing the smaller chunks manually) is a fair enough answer to this question. But of course in this case you'll be writing code to manage small allocations out of that big buffer yourself, thus negating the whole point of GC. But it might be a decent enough compromise if you like the rest of the language a lot (which Brad clearly does :-)

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