if we assume, that the number of elements N is roughly stable (so pops and pushes are roughly balanced):
• If we append and reslice, we need to reallocate every N pops, because when space runs out, append will allocate 2N elements, so it has space for N new ones. After N pop/push sequences, it will run out of space and the capacity is again N, so it will allocate a new array with 2N elements, copy over N and continue. So every N pops, we need to allocate N elements and copy N elements, but don't incur any other costs. • If we shift down, then we ~never need to reallocate, but need to copy N elements on each pop, so over N pops we need to shift N² elements So, really, the question is how (N•copy(N)) compares (alloc(N) + copy(N)). Which, as it seems to me, heavily depends on N, the memory you have, the GC pressure you have and your requirements. The answer, as always with these kinds of question is: Benchmark both on your specific machine and your specific workload. If there is a clear winner, pick that one. Otherwise, choose either. In general, I'd indeed assume that for somewhat filled fifo-queues the append-approach is faster. But I'd be willing to be surprised. On Tue, Sep 20, 2016 at 6:03 PM, Ian Davis <m...@iandavis.com> wrote: > On Tue, Sep 20, 2016, at 04:15 PM, Gabriel Adumitrachioaiei wrote: > > You might be right, but I just don't realize how. Since capacity will be > 2x or 1.5x as before, reallocating the slice will not happen often. Or do > you think that this would still be worse than copying almost all slice > everytime there is a pop ? > > > I think it depends on your use case. For the sql package I suspect the use > case is a long running process with only a few members in the slice and a > roughly level number over time. In that case the cost of copying will be > small and offset by the savings in not needing to allocate. > > However, if your use case is a a large slice that is iterated over via a > pop operation, with few or no pushes then it makes more sense to simply > reslice as you were doing in your original version. > > Ian > > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
