While profiling some datastore performance I discovered a hit where I
hadn't expected one.
It turns out that memcache is taking ~13 ms for each put/get or inc/
dec.
Since I am using a memcache atomic increment as a VM semaphore this
results in a 26ms overhead to acquire and release the "lock".
I'm sure that somewhere I read that memcache takes ~3ms for a request.
Here is the code I used to test:
MemcacheService mc =
MemcacheServiceFactory.getMemcacheService();
mc.put("testSemaphore", new Long(0));
timer.start();
for (int i = 0; i < 50; i++) {
mc.increment("testSemaphore", 1);
mc.increment("testSemaphore", -1);
}
out.append("<tr><td>Cache
increment/decrements</td><td>50</td><td>"
+ timer.elapsed() + "</td></tr>");
timer.start();
for (int i = 0; i < 50; i++) {
mc.put("testSemaphore", new Long(23));
mc.get("testSemaphore");
}
out.append("<tr><td>Cache put/gets</td><td>50</td><td>" +
timer.elapsed() + "</td></tr>");
I get ~1380ms for each of the tests, so approx 14ms for each api call.
Any suggestions?
- Martyn
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