Calc / spell check cache

[Michael Meeks]

Hi Dennis,

	Moving this to libreoffice-dev since it's generally interesting, hope
that's ok.

	Summary: we have a problem whereby calc spell-checking causes cascades
of invalidations caused by spell-checking idle handlers; it seems when
the view moves, we render, and then do lots of invalidation - which is
generally inefficient even for the PC case I guess; but particularly so
for online. Also - now we have SharedStrings so we can cache spelling
information more easily for the case of large numbers of duplicate
mis-(or correctly) spelled words - for large pivot data source ranges eg.

On 05/10/2020 11:56, Dennis Francis wrote:
> Calc perf: spell-check invalidation
> 
> Status : WIP, works mostly, need to fix the TODO items (below).

	Wonderful =)

> * WIP patch for cp-6.4 at 
>    https://gerrit.libreoffice.org/c/core/+/103941

	Thanks.

> * removed timer based spellcheck related code/members.
> * spellchecks done only when needed (paintTile -> DrawEdit etc.)
>   * results are cached with better cache-invalidation.

	Great.

> * spellcheck-results cache has two maps:
>   #1: for shared-string cells, #2: for edit-text-object cells.

	Nice.

>   #1 uses raw-pointer to rtl_uString as key.

	I guess that would work, we just need to be a bit careful we need to
make sure we clear this cache before we call:

	void SharedStringPool::purge()

	In ScDocument::~ScDocument - I think.	

>   #2 uses cell-address as key.

	Does the EditTextObject hold and cache its own spelling status ?

>   There is a third map for any special cells with a different language> set (ATTR_FONT_LANGUAGE), but it is not used for storing spellcheck
results.

	Interesting =)

> (test document used was created from first sheet of go-oox.xlsx without the
> content under "SCRIPT TYPES", refer TODO.)
> 
> * don't see unnecessary tile-invalidations on scrolling the test document.

	Wonderful =)

>   Attached the flame-graphs  with and without the fix.

	For me - I got 50% CPU use in a loolkit backend scrolling a single view
without the patch; hopefully that starts to be fast and ~free CPU-wise =)

> * TODO for the patch:
> 
>   * There is a crash on loading documents in online with cell contents with
>     asian/complex script types. Does not happen with desktop core though.

	Interesting; valgrind ?

>   * Get the document's language or whatever online sets as the language as the
>     default instead of using  ScGlobal::GetEditDefaultLanguage() (which seems to return the language associated with the default-locale), 
>     else the cache becomes inefficient in case document-language != default-locale-language.>>   * enforce cache size limits (for each internal map).

	Looks very promising.

	Thanks !

		Michael.

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