I think there is a little confusion here. That quoted description of look ups is how Multivalue works with its Hashed storage structure. Cache does NOT use a hashed storage model.
The point I really wanted to make is that Cache data files, which we refer to as Globals, do not require you to perform any kind of resizing the same way you did with Universe/Unidata. Thus reducing your operational maintenance. In addition the database as a whole, which contains all the 'globals', will grow dynamically as more data is loaded.
If you want to PM me I could set aside some time to do a short teams call with you.
Regards,
Rich Taylor
Robert,
Sorry for the slow reply. I was tied up last week and didn't get a chance to look at the community.
Not really sure what you are looking for when you say "non-linear'. As far as how records are stored in the database a multivalued records is a delimited string. In Cache when stored in the database this string is placed in a global node. The key for the node is the item id of the record stored in the MV file. So if I create a file called TEST and add a record to it when viewed with a LIST-ITEM command you might see this.
1
0001 ATTR1
0002 ATTR2
0003 ATT3
0004 ATTR4.1ýATTR4.2
If you were to view the ^TEST global where this data is stored vai the System Management Portal you would see:
^TEST = $lb(0)
^TEST(1) = "ATTR1þATTR2þATT3þATTR4.1ýATTR4.2"
See the CREATE-FILE example below.
By default, when no sort is indicated a select will select the records in key order. Note that ALL records within the database are stored the same way. It is the content and key structure that changes. In this case storing a MV record.
The speed of selects or any query in Cache is going to depend on several factors. What is the nature of the SELECT command? Are you doing any BY-EXP options here? I would suggest that if this is a serious reduction in performance I would call into the WRC or consult with your Sales Engineer. You can use the (Y and/or (Z to get more information on how this command will be executed that may help.
https://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=RVCL_commands#RVCL_commands_select
As to what CREATE-FILE does there is also some nuance to this depending on what type of file you are creating. A basic mv file created like this: CREATE-FILE TEST
will result in a VOC (MD) entry that looks like this:
TEST
0001 F
0002 ^TEST
0003 ^DICT.TEST
0004
0005
0006
0007
0008
0009
0010
Lines 1 and 2 identify globals in the Cache database the contain the data and dictionary respectively. There is a lot more information that may be recorded here too depending on the type of file, indexes, and so on. I would recommend reviewing the documentation at
https://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls
Under Technology on the left side pick 'Multivalue'
Hope all this helps
Daniel,
Excellent article both from a historical and current perspective!
Rich