[erlang-questions] Mnesia Secondary Indexes

Tom McNulty <>
Tue Jul 21 22:58:55 CEST 2009


Hi,

I moved to something similar, except instead of a gb_tree, I'm using a  
secondary table as an ordered_set, which points into the first table  
using keys: {RangeVal, Key1}.  As describe here: http://erlanganswers.com/web/mcedemo/mnesia/OrderedBy.html 
  -- thanks. It should work (haven't finished testing, and need to  
read how ordered_set is implemented).

Being 'lazy' though, I tend to want this to work to occur behind the  
scenes.


- Tom

On 21-Jul-09, at 2:34 PM, Evans, Matthew wrote:

> Hi,
>
> I recently faced a similar issue to this. I wanted to do a range- 
> based query on a table (created as a bag) where each primary key  
> could contain a large number of records (10K or so). I decided  
> against using a secondary index as a key, but instead searched using  
> a select, with a primary key and specifying a guard to do the range  
> query.
>
> As expected, these queries took a long time.
>
> To overcome this performance issue I changed the table from a bag to  
> a set and used a modified gb_tree module that returned a reference  
> to the range.
>
> For example, the old key of:
>
> KeyAsInteger
>
> Became a tuple:
>
> {KeyAsInteger,RangeValue}
>
> The modified gb_tree accepted any value in the query, and would  
> return the "closest" match. I could then use this as the RangeValue  
> in the query to the tuple.
>
>
>
> -----Original Message-----
> From:  [mailto:erlang- 
> ] On Behalf Of Tom McNulty
> Sent: Tuesday, July 21, 2009 3:14 PM
> To: 
> Subject: [erlang-questions] Mnesia Secondary Indexes
>
> Hi all,
>
> When adding an index to a table field, it appears to me (without
> looking at the source), that the indexing method is hash based. While
> this is optimal for fast secondary key lookups and join operations, it
> does not speed up range based queries.  After going through all
> available manuals, I'm quite certain it's not possible to use tree-
> based indexing on a field, but please correct me if I'm wrong.
>
> My question finally, are there an plans to add tree-based indexing to
> mnesia? And in the meantime, are there any existing projects which
> hack on this support?
>
> - Tom
>
>
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