Difference between revisions of "Calc/Performance/Cell size"
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There are a number of problems here: | There are a number of problems here: | ||
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* 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. | * 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. | ||
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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. | * 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. | ||
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Revision as of 11:04, 10 March 2008
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
[cpp,N]
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:
[cpp,N]
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.
ScFormulaCell
There are a number of problems here:
- 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.
