Here's a more succinct and to the point page: http://code.google.com/p/memcached/wiki/NewUserInternals ^ If your question isn't answered here ask for clarification and I'll update the page.
Your problem is about the slab preallocation I guess. On Tue, 6 Jul 2010, Matt Ingenthron wrote: > Hi Sergei, > > For various reasons (performance, avoiding memory fragmentation), memcached > uses a memory allocation approach called slab allocation. The memcached > flavor of it can be found here: > > http://code.google.com/p/memcached/wiki/MemcachedSlabAllocator > > Chances are, your items didn't fit into the slabs defined. There are some > stats to see the details and you can potentially do some slab tuning. > > Hope that helps, > > - Matt > > siroga wrote: > > Hi, > > I just started playing with memcached. While doing very basic stuff I > > found one thing that confused me a lot. > > I have memcached running with default settings - 64M of memory for > > caching. > > 1. Called flushALL to clean the cache. > > 2. insert 100 of byte arrays 512K each - this should consume about 51M > > of memory so I should have enough space to keep all of them - and to > > very that call get() for each of them - as expected all arrays are > > present > > 3. I call flushAll again - so cache should be clear > > 4. insert 100 arrays of smaller size ( 256K). I also expected that I > > have enough memory to store them (overall I need about 26M), but > > surprisingly to me when calling get() only last 15 where found in the > > cache!!! > > > > It looks like memcached still hold memory occupied by first 100 > > arrays. > > Memcache-top says that only 3.8M out of 64 used. > > > > Any info/explanation on memcached memory management details is very > > welcomed. Sorry if it is a well known feature, but I did not find much > > on a wiki that would suggest explanation. > > > > Regards, > > Sergei > > > > Here is my test program (I got the same result using both danga and > > spy.memcached. clients): > > > > MemCachedClient cl; > > > > @Test > > public void strange() throws Throwable > > { > > byte[] testLarge = new byte[1024*512]; > > byte[] testSmall = new byte[1024*256]; > > int COUNT = 100; > > cl.flushAll(); > > Thread.sleep(1000); > > for (int i = 0; i < COUNT; i++) > > { > > cl.set("largekey" + i, testLarge, 600); > > } > > for (int i = 0; i < COUNT; i++) > > { > > if (null != cl.get("largekey" + i)) > > { > > System.out.println("First not null " + i); > > break; > > } > > } > > Thread.sleep(1000); > > cl.flushAll(); > > Thread.sleep(1000); > > for (int i = 0; i < COUNT; i++) > > { > > cl.set("smallkey" + i, testSmall, 600); > > } > > for (int i = 0; i < COUNT; i++) > > { > > if (null != cl.get("smallkey" + i)) > > { > > System.out.println("First not null " + i); > > break; > > } > > } > > > > } > > > >
