Difference between revisions of "Calc/Performance/misc"

Revision as of 10:09, 4 July 2007

Calc Optimization 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

[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.

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.

All strings should be shared at the WorkBook level - with a single hash, doing this at the workbook level has nice properties wrt. interop with Excel shared string tables.

Mikeleib has made a quick hack for this. Try it out: IZ#63500

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. [I don't get that, what are you referring to? --erAck 02:06, 19 May 2006 (CEST)]

• 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 (6bytes), 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

The existing Data Pilot implementation doesn't have a shared normalized form of the data. (ie. with each field reduced to an ordinal, for O(1) lookup). We should implement just such a Data Pilot cache using a representation compatible with the PivotTable cache, and populatable from that on import.

threaded calculation

Ideally to scale to hyper-threaded machines we need to crunch a workbook's dependency graph & then thread the calcuation.

Similarly the process of constructing a Data Pilot cache, and (subsequently) collating that data is one that is susceptible to threading.

Chart Optimization

The existing chart component performs extremely poorly. However - it's likely that optimizing chart2 is a better bet. Having said that, there seem to often be a large number of re-calculation / re-renderings of charts on load that are perhaps realated to a calc/chart2 mis-interaction [jody- substantiate?]

In addition the chart likes to do (expensive) label / string size calculation for (potentially) tens of thousands of labels it will never use for scatter plots, multiple times each.