Re: Memory question
Martin Gregorie wrote:
If a lot of objects are marked for deletion (i.e. not about to be reused
until more objects are created) the remaining memory could get
extremely fragmented and sparse.
Huh? The only time memory fragmentation is important is when unallocated
memory gets fragmented, which doesn't happen in Java's way of things, at least
not with most of the GC algorithms in Sun's VMs. Furthermore, these
collectors don't mark dead objects for deletion, they copy live ones. And
dead ones are never re-used, not when more objects or created or any other time.
If the GC is going 6to do anything worthwhile with a sparse heap, it needs to compact the active objects,
which has the effect of reducing the number of active pages and hence
would improve paging performance.
Not true. The page from which objects are copied is active for a while, and
the page to which the objects are copied is also active for a while. Even
before the GC runs, pages that haven't been used but are not collectible can
become inactive, they will swap out and not swap in again until needed. If
they aren't needed for a while, they won't hurt paging performance.
Generally speaking whether memory is compacted has no effect on paging.
Locality of reference does, but that is not guaranteed by a compact heap.
At this point I'm speculating, so its probably wise to drop this sub
thread.
Not until the misconceptions are cleared up.
--
Lew