Managing Your AutoCAD®/RealDWG® Model Memory
Footprint for Better Performance
Bill Adkison
MarinCAD Software Engineering
CP4286-U
November 29, 2011
© 2011 Autodesk
Unconference Topic Suggestions
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Topics You All have in Mind
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Fragmentation
Large 3d models
Managing dependencies
.NET vs. ARX/Native vs LISP
Topics Bill has in Mind
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The End of the 32-bit Era (almost)
DWG Database Memory Overhead
Differing Memory Characteristics of different AutoCAD Visual Styles
Use of AcDbDatabase::reclaimMemoryFromErasedObjects(AcDbObjectIdArray)
The Advantages and Disadvantages of Disabling UNDO recording
XData versus AcDbObject::extensionDictionary
One-Shot allocation of Huge Arrays
© 2011 Autodesk
Fragmentation, Large Models
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32-bit OS: 2Gb or 3Gb limit is the real ceiling, but ragmentation within that space
in the process will slow down performance before the final limit
Even on 64-bit systems, ACAD going over ~6Mb starts slowing down a lot
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Large Models:
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PartialOpen with index structures is a good way to filter DWG content and memory
 Use INDEXCTL to create spatial and layer index structures
 Partition DWGs into Xrefs with Demand Loading
 XREF Clipping (XCLIP)
© 2011 Autodesk
.NET vs Native ARX vs LISP
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.NET is usually not a memory hog, unless you open a lot of objects
simultaneously
LISP is a LOT of overhead, but can be useful anyway for prototyping.
VLX (building a compiled LISP app) is a good way to eliminate a lot of overhead
© 2011 Autodesk
End of 32-Bit PC Era (almost)
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Migrating to x64 is good short term, and long term solution
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32-bit apps on x64 OS can save some memory, some performance cost
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AutoCAD doesn’t support x86 on x64OS, but it can be done with registry hacks (email me
for details, I have to learn them for a client anyway).
© 2011 Autodesk
AcDbDatabase Object consumption
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Big DWGs commonly have:
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~10^4 - 10^6 entities (i.e. 99% of the memory)
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~10^3 – 10^5 Symbol Table Records and XDict entries (still big, but not the typical
problem)
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Overhead of:
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16 - 32 bytes per handle/ObjectId + GS Spatial Index
 96 - 128 bytes per Entity Common Fields
 200 - >1Mb bytes per Entity
© 2011 Autodesk
Different AutoCAD Visual Styles
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2D or not 2D, That Really is the Main Question
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All non-2DWireframe modes have a common 3d GS
2D is good for:
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Others are good for:
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Model graphs with unshared nodes and static 3D viewing.
Legacy appearance (relatively uncommon, but significant)
Session with heavy document locking processing (3D Gs triggers often)
Model Graphs with shared and/or dynamic 3D viewing
Advanced rendering modes
Mem Diff: SharedNodeDwg (1024 refs to 1 block): 2D – 1.2Gb == 3D
© 2011 Autodesk
AcDbDatabase::reclaimMemoryFromErasedObjects
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Intended for scenarios repeatedly adding/erasing entities.
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~16 bytes residual per entity, out of 200b – 2Mb per entity
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Slightly better with UNDO disabled, but not much
© 2011 Autodesk
Disabling UNDO/REDO
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Very Safe by Command Line
 Not Very Effective for “common” operations with efficient UNDO recording
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Very Dangerous by API
 Disabling for specific database ops Must be self-contained
© 2011 Autodesk
XDATA vs extensionDictionary/XRECORD
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XDATA has lower overhead, about 48 bytes, plus 32 bytes per RegApp
section, then very efficient. But a 16Kb limit for XDATA per object, and you
need to share with other apps.
 extensionDictionary is about 100 bytes of overhead, plus 100 bytes per
added object. But after that, there are no capacity limits other than file size
and memory size.
© 2011 Autodesk
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© 2011 Autodesk