[Semediawiki-user] Warning: Experimental SMW Feature broken

[Michael E. <er...@di...>]

Dear list,

I had inexplicable failures in ASK queries. Some print request values 
appeared to be empty (where they shouldn't be). See my previous post 
about this:

* https://sourceforge.net/p/semediawiki/mailman/message/37596252/

Luckily SMW is open source and I could go hunting for the root cause and 
found it in the experimental feature of pre-fetching query results. It 
is used in the public fetch function of a class called ItemFetcher, 
which seems to be used for fetching the results for all ASK queries for 
all result printers. The feature switch switches between a new 
(experimental) and an old (legacy) implementation.

         if ( $this->prefetch === false ) {
             return $this->legacyFetch( $dataItems, $property, $requestOptions );
         }

I am not sure what it actually does, but disabling it solved all issues 
for me. I am using SMW 3.2.3 but a quick check indicates that this 
feature still exists as experimental in SMW 4. *Maybe it is a good idea 
to turned if off by default?!*

I got my wiki to act normal again, by adding this to LocalSettings.php:

         $smwgExperimentalFeatures = $smwgExperimentalFeatures & ~SMW_QUERYRESULT_PREFETCH;

CU,
     michael

-- 

Dr. Michael Erdmann         |er...@di...    | +49 151 6140 1790
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