RFR 8197518: Kerberos krb5 authentication: AuthList's put method leads to performance issue

Weijun Wang weijun.wang at oracle.com
Fri Feb 23 14:13:32 UTC 2018

Updated at http://cr.openjdk.java.net/~weijun/8197518/webrev.02/.

1. ConcurrentHashMap used in MemoryCache. No more "content.remove(key)" but it's actually useless because rc.isEmpty() will not be true normally. I'll think about how to clean up unused AuthList objects in another RFE.

2. AuthList now removes entries from tail backwards until one is within lifespan. I still kept an oldestTime field. In my experiment it is useful but a bigger value does not help much, so I just hardcoded it to 5 seconds.


> On Feb 23, 2018, at 4:57 PM, Weijun Wang <weijun.wang at oracle.com> wrote:
> Brilliant idea. I will do more experiment.
> Thanks
> Max
>> On Feb 23, 2018, at 11:25 AM, Xuelei Fan <xuelei.fan at oracle.com> wrote:
>> Hi Weijun,
>> I thought more about the performance impact.  The impact may mainly come from the big size of the cached entries.
>> The current implementation needs to go over the full list: find the 1st expired item and then remove the rest.  The previous one have an additional round with entries.indexOf().  Could we just start from the end of the list?
>>   while (true) {
>>      E e = entries.removeLast();
>>      if e not expired {
>>         add it back and break;
>>      }
>>   };
>> If the list is really big, and the lifetime is significant big as well (>> 1 minute), iterate from the oldest item (backward from the end of the list) may be much more effective.  LinkedList itself is not synchronized, so as if there is not too much items to go over, the performance should be fine.  I'm hesitate to hard code a cleanup every 1 minute strategy.  If we clean often, there may be not too much items to go over in the list.  So we might be able to remove the "at most every minute" strategy.
>> Xuelei
>> On 2/22/2018 5:55 PM, Weijun Wang wrote:
>>> Updated webrev at http://cr.openjdk.java.net/~weijun/8197518/webrev.01/.
>>>> On Feb 23, 2018, at 9:02 AM, Weijun Wang <weijun.wang at oracle.com> wrote:
>>>> You mean I can save it somewhere and only update it when a cleanup is performed?
>>>> This should be better. Now there will be only isEmpty(), getFirst() and addFirst(), and one less getLast().
>>>> Thanks
>>>> Max
>>>>> On Feb 23, 2018, at 1:45 AM, Xuelei Fan <xuelei.fan at oracle.com> wrote:
>>>>> Looks like list synchronization is a factor of the performance impact. Maybe, you can have a private time for the oldest entry so don't access/iterate/cleanup entries list until necessary.  The "at most every minute" may be not a good strategy in some situations.
>>> In fact, it's now almost "exactly every minute". What situations do you think it's not good? I cannot use size() because I have to remember all entries with lifespan to be correct.
>>> Thanks
>>> Max
>>>>> Xuelei
>>>>> On 2/22/2018 12:36 AM, Weijun Wang wrote:
>>>>>> Please take a review at
>>>>>>  http://cr.openjdk.java.net/~weijun/8197518/webrev.00/
>>>>>> Two notes:
>>>>>> 1. I tried list.subList(here, end).clear() but it's not faster.
>>>>>> 2. I have looked at ConcurrentHashMap + ConcurrentSkipListMap but will need more time to verify its correctness and measure the performance gain. Since the bug is reported on 8u, a safer fix looks better.
>>>>>> Noreg-perf.
>>>>>> Thanks
>>>>>> Max

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