Question
· Oct 8, 2022

How much memory will it take to use maxlen for String type?

#Caché

Hi Friends,

If I created Property as below

Property Abc as %String (Maxlen = 3000000)

how much space will be used in cache DB, if assigned "hello" to Abc?

The cache will use 3000000  bytes or  5 bytes?

This conformation is very important for my implementation

Thanks,

Prashanth

Product version: IRIS 2022.1
Discussion (3)1
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Julius Kavay · Oct 8, 2022

For a string like "hallo" Cache will use 5+2 = 7 bytes. If that "hallo..." is longer then 253 bytes then length_of_string + 4 bytes will be used and if your "hallo..." is longer then 65535 bytes then length_of_string + 6 bytes will be used.

But there is one more thing, you should know: the sum of the lengths of ALL properties, except the array(like) properties, can't be greater then that famous 3641144 magic number (if you use the standard Cache Storage). Array-like properties are those, which are stored in own nodes.

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Alex Woodhead · Oct 9, 2022

Hi Prashanth,

It is possible to view how this is stored.

Consider the following class definition.

After compiling its default Data Storage location is global: ^TEST.PropertyLenD

 Class TEST.PropertyLen Extends %Persistent
{
Property Abc As %String(MAXLEN = "");
Property Def As %String(MAXLEN = "");

Storage Default
{
<Data name="PropertyLenDefaultData">
<Value name="1">
<Value>%%CLASSNAME</Value>
</Value>
<Value name="2">
<Value>Abc</Value>
</Value>
<Value name="3">
<Value>Def</Value>
</Value>
</Data>
<DataLocation>^TEST.PropertyLenD</DataLocation>
<DefaultData>PropertyLenDefaultData</DefaultData>
<IdLocation>^TEST.PropertyLenD</IdLocation>
<IndexLocation>^TEST.PropertyLenI</IndexLocation>
<StreamLocation>^TEST.PropertyLenS</StreamLocation>
<Type>%Storage.Persistent</Type>
} }

Creating a record:

USER>s o=##class(TEST.PropertyLen).%New()
 
USER>s o.Abc="Hello"
 
USER>s o.Def="World!"
 
USER>d o.%Save()
 
USER>w !,"RowId is ",o.%Id()
 
RowId is 1

Then viewing the record

zw ^TEST.PropertyLenD(1)
^TEST.PropertyLenD(1)=$lb("","Hello","World!")
 
USER>

So by default there is a single global data node made from a list of all property values.

This can also can be viewed in System Management Portal -> System Explorer -> Globals:

Kind regards,

Alex

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