Difference between revisions of "Calc/Performance/misc"
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* Document pointer - as in the ScEditCell structure we lug around a document pointer we should 'know' as implicit context. | * Document pointer - as in the ScEditCell structure we lug around a document pointer we should 'know' as implicit context. | ||
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+ | * Shared formulae - Excel will 'share' formulae - ie. very little state is duplicated if you fill a column 'D' with =((A1+B1)/C1)* SQRT(A1) or whatever. Calc by contrast will duplicate this formulae innumerable times. We need to extract immutable, position independant formula objects, reference count & share these; plus of course, elide duplicates on import. This would give a massive memory saving for large sheets - it's very common to share formulae. | ||
+ | |||
+ | * Splitting Matrix pieces - perhaps possible to split: nMatCols, nMatRows (4bytes), pMatrix (4-8bytes), and perhaps cMatrixFlag (1byte) into a derived 'ScMatrixFormula' sub-class ? specific to matrix formulae: a sub-set of formulae. | ||
=== In-sheet objects === | === In-sheet objects === |
Revision as of 10:34, 20 March 2006
Contents
Calc Optimisation Opportunities
There are a lot of opportunities in calc for various reasons. This list needs extending:
Cell size
Basic problem: the most basic cell consumes about 50bytes all told, more complex cells consume far more memory, there are a number of simple & obvious things to re-factor here.
It's trivial to calculate the average cost - simply create a sheet with several thousand cells in it, and measure the heap allocation change on load - with memprof or some other tool, then divide by the number of cells. Similarly, wins are easy to measure this way.
ScBaseCell
sc/inc/cell.hxx; code in sc/source/core/data/cell.cxx & cell2.cxx
class ScBaseCell { protected: ScPostIt* pNote; SvtBroadcaster* pBroadcaster; USHORT nTextWidth; BYTE eCellType; // enum CellType - BYTE spart Speicher BYTE nScriptType;
Every cell carries this overhead; note that a chunk of it is not necessary for many cells:
- ScPostIt pointer - very, very infrequently used - we have almost no post-it note per cell.
- SvtBroadcaster - used by cells that are referenced (by a single cell (ie. non-range) reference) from another cell - again, a sub-set of all cells.
Solutions: a little re-factoring required, but stealing a bit-field from eCellType to denote a 'special' cell:
class ScBaseCell { protected: USHORT nTextWidth; BYTE eCellType : 7; // enum CellType - BYTE spart Speicher bool bSpecial : 1; // other information to be looked up elsewhere BYTE nScriptType;
The 'bSpecial' flag could be used to denote that there is a 'note' for this cell (in a separate hash), or that this cell has a single-cell dependant. So - we can save 2/3rds of the base size with fairly little effort.
ScStringCell
In Excel similar strings across the sheet are shared. Our string class includes a sharable, immutable reference counted string - but it's not clear that we use this as intelligently as we should - pwrt. XML import / export. Possibly we should be trying to detect common strings there with a small back-hash.
ScFormulaCell
There are a number of problems here:
- redundant data: apparently we store redundant data for values. Certainly we store the 'rendered' or computed value of the cell regardless of whether it is likely to be rendered.
- ScFormulaCell inherits from svt/inc/listener.h - which has a virtual destructor, hence we have a vtable pointer per instance too (most likely unnecessary), as well as the listener list.
- Document pointer - as in the ScEditCell structure we lug around a document pointer we should 'know' as implicit context.
- Shared formulae - Excel will 'share' formulae - ie. very little state is duplicated if you fill a column 'D' with =((A1+B1)/C1)* SQRT(A1) or whatever. Calc by contrast will duplicate this formulae innumerable times. We need to extract immutable, position independant formula objects, reference count & share these; plus of course, elide duplicates on import. This would give a massive memory saving for large sheets - it's very common to share formulae.
- Splitting Matrix pieces - perhaps possible to split: nMatCols, nMatRows (4bytes), pMatrix (4-8bytes), and perhaps cMatrixFlag (1byte) into a derived 'ScMatrixFormula' sub-class ? specific to matrix formulae: a sub-set of formulae.
In-sheet objects
With a relatively modest number of in-sheet objects (which are favorite tools of complex spreadsheet creators) things become horribly slow: 30secs to load a small file with ~no data / macros & only 240 list boxes sample document.
The sheet objects need idly creating in the svx layer; also there is a floating patch to improve VCL's control management performance - wherein some of the problems lie.
Large / complex pivot sheets
Jody has some sample data here - links ? - internal Novell sheet (commonly used) taking ~3 hours to re-compute.
threaded calculation
Ideally to scale to hyper-threaded machines we need to crunch a workbook's dependency graph & then thread the calcuation.