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Update the FormulaEvaluator performance section to match current behaviour

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git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1348657 13f79535-47bb-0310-9956-ffa450edef68
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Nick Burch 2012-06-10 20:40:32 +00:00
parent 99fcaf0edb
commit c7fd6d3212
1 changed files with 37 additions and 24 deletions
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61
src/documentation/content/xdocs/spreadsheet/eval.xml
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@ -272,28 +272,41 @@ for(int sheetNum = 0; sheetNum < wb.getNumberOfSheets(); sheetNum++) {
</source>
</section>
<anchor id="Performance"/>
<section><title>Performance Notes</title>
<ul>
<li>Generally you should have to create only one FormulaEvaluator
instance per sheet, but there really is no overhead in creating
multiple FormulaEvaluators per sheet other than that of the
FormulaEvaluator object creation.
</li>
<li>Also note that FormulaEvaluator maintains a reference to
the sheet and workbook, so ensure that the evaluator instance
is available for garbage collection when you are done with it
(in other words don't maintain long lived reference to
FormulaEvaluator if you don't really need to - unless
all references to the sheet and workbook are removed, these
don't get garbage collected and continue to occupy potentially
large amounts of memory).
</li>
<li>CellValue instances however do not maintain reference to the
Cell or the sheet or workbook, so these can be long-lived
objects without any adverse effect on performance.
</li>
</ul>
</section>
</body>
<anchor id="Performance"/>
<section><title>Performance Notes</title>
<ul>
<li>Generally you should have to create only one FormulaEvaluator
instance per Workbook. The FormulaEvaluator will cache
evaluations of dependent cells, so if you have multiple
formulas all depending on a cell then subsequent evaluations
will be faster.
</li>
<li>You should normally perform all of your updates to cells,
before triggering the evaluation, rather than doing one
cell at a time. By waiting until all the updates/sets are
performed, you'll be able to take best advantage of the caching
for complex formulas.
</li>
<li>If you do end up making changes to cells part way through
evaluation, you should call <em>notifySetFormula</em> or
<em>notifyUpdateCell</em> to trigger suitable cache clearance.
Alternately, you could instantiate a new FormulaEvaluator,
which will start with empty caches.
</li>
<li>Also note that FormulaEvaluator maintains a reference to
the sheet and workbook, so ensure that the evaluator instance
is available for garbage collection when you are done with it
(in other words don't maintain long lived reference to
FormulaEvaluator if you don't really need to - unless
all references to the sheet and workbook are removed, these
don't get garbage collected and continue to occupy potentially
large amounts of memory).
</li>
<li>CellValue instances however do not maintain reference to the
Cell or the sheet or workbook, so these can be long-lived
objects without any adverse effect on performance.
</li>
</ul>
</section>
</body>
</document>