Max size limit for a %Library.DynamicObject variable

No, there is no limit for the size of %Library.DynamicObject, but the  %ToJSON() might give a <MAXSTRING> - here is a workaround for such: 

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls...

The object doesn't throw the <MAXSTRING> error. However variable do. If your serialization the JSON and stored into variable. If it's reaches the maximum string it will throw an error.

Internally, a %DynamicArray or %DynamicObject is usually limited only by the amount of memory that the OS is willing to allocate to the job,  Because the components of such objects are not limited by their size, some very large components need to be allocated by a non-standard allocator that does not participate with the $ZSTORAGE limit.  But some components of a %DynamicObject/Array are allocated by the usual memory allocator so %ZSTORAGE might limit the size.

Since %DynamicObject/Array classes are always stored in memory (I once built one that needed 20GB of memory) you want to limit how many large objects are active at the same time.  When you encounter a large %DynamicObject/Array you want to move its data to a file or global %Stream before you start reading in another large %DynamicObject/Array,

The %FromJSON(…) method can create a %DynamicObject/Array while reading JSON from any kind of %Stream.  The %ToJSON(…) method can write JSON text to any kind of %Stream.  A %Stream is not usually limited by the max supported length of an ObjectScript string and the %FromJSON and %ToJSON methods read/write %Stream data using buffers smaller than the max supported string length.

If you have a %DynamicObject/Array with a string component larger than the ObjectScript max string length then you can use the three argument %Get(key,default,type) method where the ‘type’ argument specifies a “stream” type.  The resulting %Stream is still stored in memory but that %Stream is readonly and will often share the memory allocation with string component in the %DynamicObject/Array. That in-memory %Stream can be copied into a file or global %Stream.  The three argument %Set(key,value,type) method can create a %DynamicObject/Array component of any length when the ‘type’ argument specifies that the ‘value’ argument is a %Stream.  If the %Set ‘value’ argument is a readonly, in-memory %Stream created by %Get(key,default,”stream”) then the component created by %Set will usually share in-memory data with its  ‘value’ argument stream.

See the class reference documentation for %Get and %Set.  The ‘type’ argument options include the capabilities to encode to, or to decode from, BASE64 representation.  This can be useful when working with a BASE64 encoded .pdf file in a JSON object.