Sorry for no reply for so long. I found this feature can cause some problem if some UDF did not implemented properly. When we using UDF, this feature requires that a UDF implement a 'getDisplayString' method which returns a unique string that can represent the UDF and it's input parameters. The unique 'displayString' is used as key for the evaluation cache. So, problem happen when those two criteria are satisfied: 1. We use more than one UDF in one hql session 2. The 'getDisplayString' method of the UDFs in use return same string for different UDFs.
I think it's worth to point this dependency out in the UDF related documents or 'cache.expr.evaluation' document. 2014-07-04 14:37 GMT+08:00 Lefty Leverenz <leftylever...@gmail.com>: > The 'hive.cache.expr.evaluation' parameter is documented in the wikidoc > Configuration > Properties > <https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.cache.expr.evaluation>. > Have you added other information in a different wikidoc? If so, I'll link > the docs to each other. > > -- Lefty > > > On Thu, May 29, 2014 at 5:31 AM, Lefty Leverenz <leftylever...@gmail.com> > wrote: > >> Thank you for pointing this out. The 'hive.cache.expr.evaluation' >> parameter was added by HIVE-4209 >> <https://issues.apache.org/jira/browse/HIVE-4209> and it needs to be >> included in the wiki. Its description is in hive-default.xml.template: >> >> If true, evaluation result of deterministic expression referenced twice >>> or more will be cached. For example, in filter condition like ".. where key >>> + 10 > 10 or key + 10 = 0" "key + 10" will be evaluated/cached once and >>> reused for following expression ("key + 10 = 0"). Currently, this is >>> applied only to expressions in select or filter operator. >> >> >> Do you want to provide more information than that? To contribute to the >> wiki, create a Confluence account >> <https://cwiki.apache.org/confluence/signup.action> and send a message >> to this list asking for wiki editing privilege and giving your account >> name. But if you just want the description to be added to the wiki, I can >> take care of that. >> >> If you have additional information, it might not belong in Configuration >> Properties >> <https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties> >> (although >> once the parameter is there it can link to another page for details). The >> Select >> <https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Select> >> page is one possibility, or maybe you'll find a better place for it. >> >> If you want to revise the description in hive-default.xml.template, you >> need to open a JIRA and patch the file. >> >> >> -- Lefty >> >> >> On Sat, May 24, 2014 at 1:01 AM, 郭士伟 <guoshi...@gmail.com> wrote: >> >>> I have used a configuration property 'hive.cache.expr.evaluation' in >>> hive 0.12 recently and found it useful. But I cannot find any documents >>> about it on the wiki page: >>> https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties. >>> Indeed, I pick it up from the source code. >>> >>> I think it maybe useful for other hive users if I can write some >>> documents about the property. >>> >>> So, can anyone give me some pointers that how can I make the change >>> happen ? >>> >>> Thanks, anyway. >>> >> >> >
