Here is a simple patch against 1.2.2 that should increase the memory
usage efficiency in certain cases. We've been running it stable for a
few days without problems, and it works as expected. It just checks to
see if the last item in the LRU is expired before allocating space for
the new item. In the case that it is expired, remove it before
allocating. That has the effect of replacing the oldest item in that
size, if possible. It won't help in all cases, but if slabs have
different write and expiry profiles, it may help keep them in check. In
the extreme case, it may even keep the total memory usage well below the
maximum, when it would currently fill with expired data. It would be a
big help if certain slab sizes see much higher write load than others,
but those writes have a short expiry time.
Timo
--- items.c.orig 2007-08-16 14:46:18.000000000 -0600
+++ items.c 2007-08-16 14:46:51.000000000 -0600
@@ -82,6 +82,11 @@
if (id == 0)
return 0;
+ /* Try to keep memory usage to a minimum by removing/replacing the last
item
+ * in the queue if it has already expired, instead of allocating more
space.
+ */
+ if (tails[id] != 0 && tails[id]->refcount == 0 && tails[id]->exptime != 0
&& tails[id]->exptime < current_time)
+ do_item_unlink(tails[id]);
it = slabs_alloc(ntotal);
if (it == 0) {
int tries = 50;
