Hi Clinton, sure, I'll add the Jira ticket for this, but since here in Italy, because of the timezone, started celebrating the new year, I'll do it tomorrow :P BTW, I discourage the use of the test
value == Cache.NULL_OBJECT but rather Cache.NULL_OBJECT.equals(vaue) I had to patch iBatis 2 (and reported to the dev ML, see http://markmail.org/message/lm752wxm2jwcpg5l), with this last check to use a distribuited cache. My scenario was: the same iBatis application replicated on more than one application server (on different servers) more than one memcached node server as cache storage. Moreover, Cache.NULL_OBJECT has to be Serializable. Happy new year and tanks for your replies!!! :) Best regards, Simone Tripodi On Thu, Dec 31, 2009 at 5:11 PM, Clinton Begin <clinton.be...@gmail.com> wrote: > PS: I just had a look, and I doubt there's any chance of a race condition > here... there's only two usages of hasKey(). One is thread local, and the > other uses a read/write lock scope. > > That said, I think your point about performance is perfectly warranted, and > quite simple to solve. For example: > > if (cache.hasKey(key)) { > return (List) cache.getObject(key); > }... > > Becomes: > > Object value = cache.getObject(key) > if (value != null) { > return Cache.isNull(value) ? null : value; > }... > > Where Cache.isNull(value) simply checks if value == Cache.NULL_OBJECT. Of > course you could just do that outside too, but I think having a method like > this makes it nicer to read. > > Do you want to add a Jira ticket for this? > > Clinton > > On Thu, Dec 31, 2009 at 9:04 AM, Clinton Begin <clinton.be...@gmail.com> > wrote: >> >> Good points. >> >> I think the only reason hasKey exists is to support cached null values. >> But that said, I believe in iBATIS 2 I used a NULL_OBJECT value to represent >> the difference between "yes I'm cached, and I'm null" vs. "I'm not cached". >> >> So I think there definitely is something to look at here. >> >> Clinton >> >> On Thu, Dec 31, 2009 at 5:38 AM, Simone Tripodi <simone.trip...@gmail.com> >> wrote: >>> >>> Hi all guys, >>> since I've been integrating 3rd part caching solutions[1] in iBatis3, >>> I started thinking about the use of method in the Cache interface: >>> >>> org.apache.ibatis.cache.Cache#hasKey() >>> >>> Honestly, I'm a little scared about the use for a key check, as it may >>> expire between checking for the key, and whatever you want to do with >>> the stored object, and produce a race condition :( >>> I'd propose to remove this method, and let to the layer built on top >>> of cache interface checking if the retrieved object is not null. >>> >>> Indeed, some distribuited and scalable caching servers like >>> memcached[2] don't provide methods to key checking, because of the >>> reason above. Moreover, in this scenario, the only way I have to check >>> if a key is present in the cache, is getting the object, and checking >>> it is null. But let's suppose I've a cached Object of 10M size, >>> checking first and then getting if present, causes 20M net traffic :( >>> >>> Please don't get me wrong, I don't want to criticize the excellent >>> work you've been doing - I don't use different persistence layer than >>> iBatis! - but since iBatis is largely used in production environments, >>> I would encourage the community to be sensible to this kind of >>> potential issues. >>> >>> What do you think about it? Have a nice end of the year party and see >>> you next year! :D >>> Best regards, >>> Simone Tripodi >>> >>> [1] http://ibaguice.googlecode.com/svn/site/1.0-SNAPSHOT/caching.html >>> [2] http://memcached.org/ >>> >>> -- >>> http://www.google.com/profiles/simone.tripodi >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: user-java-unsubscr...@ibatis.apache.org >>> For additional commands, e-mail: user-java-h...@ibatis.apache.org >>> >> > > -- http://www.google.com/profiles/simone.tripodi --------------------------------------------------------------------- To unsubscribe, e-mail: user-java-unsubscr...@ibatis.apache.org For additional commands, e-mail: user-java-h...@ibatis.apache.org
