Hi Ivan,
One idea to consider is an indirection that spreads the work over
multiple Cache implementations.
Similar to what ConcurrentHashMap does, doing an early fan out to
multiple Caches based on the key.
If it was keyed to the same key as the cache, it would be able to take
advantage of re-using the contexts.
Though I'm not sure how to size or re-size the index based on load or ...
I would think that using a 'small' cache size would bound the expunge
time and still allow some-reuse.
$.02, Roger
On 11/8/2017 2:09 PM, Ivan Gerasimov wrote:
Thank you Bernd for looking into this!
On 11/7/17 11:42 PM, Bernd Eckenfels wrote:
Hello,
There is already a property to set the cache size, would it be enough
to re-purpose a cache size of 0 to turn it off?
Currently, setting the cache size to 0 means that it is unbounded, so
that the entries are removed from the cache only when they get expired.
Are there numbers to show when this is actually a problem? Is this
only for 100% Cache misses?
We've seen dumps with lots of threads blocked waiting on the
Cache.get()/put()/remove().
This is primarily due to the time spent in the cache cleaning routines
(see
sun.security.util.MemoryCache.emptyQueue()/expungeExpiredEntries()),
which are executed inside the synchronization block.
This time is linear on the size of cache, but limiting the cache size
doesn't always help either, as the amount of cleanup work also
increases with a bounded cache.
Allowing to avoid to use the cache removed this bottleneck and under
certain conditions the throughput increased from 35 to 120 sessions
per second.
Please note that the proposed option javax.net.ssl.needCacheSessions
will be true by default, so the default behavior will not change.
Only in specific situation, if it is proved that turning off the cache
will improve performance, this option will be recommended to be set to
false.
Maybe the cache itself needs some optimizations?
Certainly, it would be very good to optimize the cache implementation!
I've made a few attempts, but failed to achieve a significant
improvement in different scenarios.
The complication is due to the two requirements: maintaining fixed
cache capacity and maintaining FIFO order when removing the entries.
This makes it hard to use the concurrent data structures as is.
Still, I'm totally for the cache optimization in JDK 10, if it is
possible.
However, if it is done, it would not be probably backported to the
earlier releases.
And I'm going to propose to backport the proposed fix with the option
to turn off the cache, as it will be useful for some currently running
applications.
With kind regards,
Ivan
(It is hard to imagine that a saved handshake does not compensate for
hundreds of gets - especially if the current version still would
generate a cache key)
Gruss
Bernd
Gruss
Bernd
--
http://bernd.eckenfels.net
------------------------------------------------------------------------
*From:* security-dev <security-dev-boun...@openjdk.java.net> on
behalf of Ivan Gerasimov <ivan.gerasi...@oracle.com>
*Sent:* Wednesday, November 8, 2017 3:24:54 AM
*To:* security-dev@openjdk.java.net
*Subject:* [10] RFR : 8186628 : SSL session cache can cause a
scalability bottleneck
Hello everybody!
The class sun.security.ssl.SSLSessionContextImpl maintains caches for
the sessions reuse.
Access to the cache from threads is serialized.
It was reported that under heavy load the time of waiting for the turn
to access the synchronized methods outweighs the time of creating a new
session.
It is proposed to introduce a flag that will allow to avoid using the
cache altogether.
Would you please help review the proposed fix?
BUGURL: https://bugs.openjdk.java.net/browse/JDK-8186628
WEBREV: http://cr.openjdk.java.net/~igerasim/8186628/00/webrev/
<http://cr.openjdk.java.net/%7Eigerasim/8186628/00/webrev/>
--
With kind regards,
Ivan Gerasimov
--
With kind regards,
Ivan Gerasimov
