[Glass] Where are indices really useful ?

Norm Green via Glass glass at lists.gemtalksystems.com
Sat Jan 28 08:29:03 PST 2017

That's correct.  With a low selectivity query (aka large result set), 
most of the time can be spent constructing the result set. The 
#selectAsStream: methods avoid this penalty.

Also Dale is working on a major overhaul of the indexing system in 3.4.  
Indexing should perform better in that release.


On 1/28/2017 8:24 AM, Marten Feldtmann via Glass wrote:
> Ok, I read the documentation and I understand where the problem is:
> The query support creates a temporary container to held the result and 
> then you iterate over the result container. I assume, that it takes 
> time to create and maintain this result container (if the result size 
> is larger). The example below can be transferred into a streamable 
> query, which speed ups the query by at least a factor of 2.
> Marten
>> Marten Feldtmann via Glass <glass at lists.gemtalksystems.com> hat am 
>> 28. Januar 2017 um 16:03 geschrieben:
>> Yes, I know: indices are a world of their own. But I asked myself, 
>> what can an index bring for me.
>> I had an IdentitySet with around 3759515 elements. The objects 
>> contained have several attributes, but I am only considering one 
>> attribute for my queries via GsQuery: the attribute instances are 
>> member of SmallDouble, no nil containing.
>> I produced a query like:
>> "(40,0 <= each.floatvalue <= 60,0)"
>> and the results are around 1719852 elements (around 50 % of the total 
>> numbers of elements). I do not select the returned objects I just 
>> count them.
>> When I define an index on this set (equalityIndex) it took around 6 
>> seconds to count them all, without index creation the system get the 
>> job done in 2.5 seconds. (always a warm database).
>> SQLite3 takes around 0.7s without index and 0.17s with index (total 
>> numbers are not useful here, but it shows that here an index is useful).
>> It seems for me, that an index in Gemstone is useful, IF the number 
>> of expected elements are really small .
>> Any comment ?
>> Marten
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