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Managing Your AutoCAD®/RealDWG® Model Memory Footprint for Better PerformanceBill AdkisonMarinCAD Software Engineering

CP4286-U November 29, 2011

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Unconference Topic Suggestions

Topics You All have in Mind Fragmentation Large 3d models Managing dependencies .NET vs. ARX/Native vs LISP

Topics Bill has in Mind 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

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Fragmentation, Large Models

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

Large Models: 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)

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.NET vs Native ARX vs LISP

.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

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End of 32-Bit PC Era (almost)

Migrating to x64 is good short term, and long term solution

32-bit apps on x64 OS can save some memory, some performance cost 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).

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AcDbDatabase Object consumption

Big DWGs commonly have:

~10^4 - 10^6 entities (i.e. 99% of the memory)

~10^3 – 10^5 Symbol Table Records and XDict entries (still big, but not the typical problem)

Overhead of: 16 - 32 bytes per handle/ObjectId + GS Spatial Index 96 - 128 bytes per Entity Common Fields 200 - >1Mb bytes per Entity

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Different AutoCAD Visual Styles

2D or not 2D, That Really is the Main Question

All non-2DWireframe modes have a common 3d GS 2D is good for:

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)

Others are good for: Model Graphs with shared and/or dynamic 3D viewing Advanced rendering modes

Mem Diff: SharedNodeDwg (1024 refs to 1 block): 2D – 1.2Gb == 3D

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AcDbDatabase::reclaimMemoryFromErasedObjects

Intended for scenarios repeatedly adding/erasing entities.

~16 bytes residual per entity, out of 200b – 2Mb per entity

Slightly better with UNDO disabled, but not much

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Disabling UNDO/REDO

Very Safe by Command Line Not Very Effective for “common” operations with efficient UNDO recording

Very Dangerous by API Disabling for specific database ops Must be self-contained

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XDATA vs extensionDictionary/XRECORD

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.

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