Comments on: What is a “large” select list? http://nebula-rnd.com/blog/tech/mv/d3/2009/08/d3selectlist1.html Welcome to the Nebula Fri, 06 Jan 2012 09:44:06 +0000 hourly 1 http://wordpress.org/?v=3.1 By: Tony Gravagno http://nebula-rnd.com/blog/tech/mv/d3/2009/08/d3selectlist1.html/comment-page-1#comment-333 Tony Gravagno Mon, 10 Aug 2009 18:37:09 +0000 http://nebula-rnd.com/blog/?p=362#comment-333 Danny, you are correct that you need to SID through a list in a dynamic array no matter where it comes from. Most people are familiar with how frames link. I was clarifying that a dynamic array in a traditional VME environment, without Flash, still needs to use frame space. This includes lists generated with Execute "select foo" rather than Select FileVar. The Execute statement generates a big list that needs to be scanned while Select sets up a cursor to file space and positions through each item of each group. In a dynamic environment someone adds items to the file after an Execute, you won't see it, but you will see new items added after your Select. The option one uses is dependent on the purpose. It would be a neat feature if you could point to a file item and read it "as-list" so that you could readnext through it with a cursor to the file space rather than pulling the whole thing into workspace, thus duplicating static data. Maybe this is the way it works internally, I dunno. I'm no engineer but since I'm the only person talking about this sort of thing in public I'll share what I believe is accurate until someone corrects me. :) About jBase, Jim Idle recently commented on this topic here: http://groups.google.com/group/jBASE/browse_frm/thread/fc5767b575e9bb0c Danny, you are correct that you need to SID through a list in a dynamic array no matter where it comes from. Most people are familiar with how frames link. I was clarifying that a dynamic array in a traditional VME environment, without Flash, still needs to use frame space. This includes lists generated with Execute “select foo” rather than Select FileVar. The Execute statement generates a big list that needs to be scanned while Select sets up a cursor to file space and positions through each item of each group. In a dynamic environment someone adds items to the file after an Execute, you won’t see it, but you will see new items added after your Select. The option one uses is dependent on the purpose.

It would be a neat feature if you could point to a file item and read it “as-list” so that you could readnext through it with a cursor to the file space rather than pulling the whole thing into workspace, thus duplicating static data. Maybe this is the way it works internally, I dunno. I’m no engineer but since I’m the only person talking about this sort of thing in public I’ll share what I believe is accurate until someone corrects me. :)

About jBase, Jim Idle recently commented on this topic here:
http://groups.google.com/group/jBASE/browse_frm/thread/fc5767b575e9bb0c

]]> By: dannyruckel http://nebula-rnd.com/blog/tech/mv/d3/2009/08/d3selectlist1.html/comment-page-1#comment-331 dannyruckel Mon, 10 Aug 2009 15:43:55 +0000 http://nebula-rnd.com/blog/?p=362#comment-331 Tony, Regardless of where your "list" is held, in a variable or in frame space, won't you still have to "SID" through the list? In the "Factors for Consideration" heading, "This has less to do with a number of attributes and more to do with volume of data, or the LEN() of the variable containing the dynamic array." strikes me as the meat of the matter. What's not clear to me is determining that threshold in a general sense. I guess what I'm driving at is, when you are coding at some point you are going to have to say, "Hmmm, the volume of data I'm going to typically deal with here is {some value} and that crosses (or doesn't cross) a certain threshold and because of that I'm going to process this list as a "LARGE" list. In jBase, by default, does it really maintain a pointer in a dynamic list as you iterate through it or do you have to use the "REMOVE" command? I worked in the jBase environment a number years before stumbling into D3 and don't recall that jBase was "kind enough" ;) to maintain that pointer. As always, thank you for your thorough response/s. Danny Tony,

Regardless of where your “list” is held, in a variable or in frame space, won’t you still have to “SID” through the list?

In the “Factors for Consideration” heading, “This has less to do with a number of attributes and more to do with volume of data, or the LEN() of the variable containing the dynamic array.” strikes me as the meat of the matter. What’s not clear to me is determining that threshold in a general sense. I guess what I’m driving at is, when you are coding at some point you are going to have to say, “Hmmm, the volume of data I’m going to typically deal with here is {some value} and that crosses (or doesn’t cross) a certain threshold and because of that I’m going to process this list as a “LARGE” list.

In jBase, by default, does it really maintain a pointer in a dynamic list as you iterate through it or do you have to use the “REMOVE” command? I worked in the jBase environment a number years before stumbling into D3 and don’t recall that jBase was “kind enough” ;) to maintain that pointer.

As always, thank you for your thorough response/s.

Danny

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