[postgis-devel] SoC] GSoC 2021 - Week 10 Report - Implement pre-sorting methods before GiST index building

[Han Wang]

Hi all,
I am here to share with you my Week 10 report. You can also find it at [1]
Coding Week 10 (9th August - 15th August)
<https://trac.osgeo.org/postgis/wiki/ImplementSortingMethodsBeforeGistIndexBuilding#CodingWeek109thAugust-15thAugust>

*Coding Phase *:

   - Do more traversal tests
   - Fix the issue of gist_page_items

*Plans for next week*:

   - Submit the final evaluation
   - Plan for a 32 bit hash function
   - Finish the documents

I have updated the document[2] for more tests. The pre-sort function works
normally. But from this test, I think the current implementation of the
fast index building method with pre-sorting may cause a loss of
performance.
The pre-sorting function entry in Postgres does not check the leaf elements
of a GiST index. And the first 32-bit of a 64bit Morton/Hilbert hash code
as a datum key may reduce the precision significantly.
>From my perspective, a 32 bit hash function may be necessary next. If you
have any questions or suggestions, please let me know! You can reach me at
the #postgis channel in matrix.

[1]
https://trac.osgeo.org/postgis/wiki/ImplementSortingMethodsBeforeGistIndexBuilding
[2]
https://docs.google.com/document/d/1m4oxBAsKCyjAnYmkCmQ0X_ltiid5tliFwF3rtdzlKsc/edit?usp=sharing

Best regards,
Han
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