[GSoC] Abhradeep's GSoC blogs (27 Jun, 2022 IST)

[Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>]

Hello developers, this is the thread where you can know about
my weekly GSoC blog links.

My Project - Reachability bitmap improvements

Blog update
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Title - GSoC Week 2: redesign the table format
Blog link - https://medium.com/@abhra303/gsoc-week-2-redesign-the-table-format-829dae755a5

Summary - 

In the last week, I worked on the reviews. Some major requested
changes are (1) Use commit positions instead of commit oids in
the table. (2) Use 8 byte offset positions instead of 4 bytes
(3) use iterative approach for parsing xor bitmaps (4) Use
`<commit_pos, offset, xor_pos>` triplets.

While implementing these changes, I discovered some bugs in the
previous version. I faced errors during this time. But finally
managed to fixed those errors. Taylor helped me to get rid of
some errors.

I think that we can optimise the parsing of xor bitmaps further
by stopping stack filling loop when we get an already parsed
bitmap since we know that bitmaps having xor relations with it
has already been stored/parsed.


Previous blogs 
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Title - GSoC Week 1: Let's Get started
Blog link - https://medium.com/@abhra303/gsoc-week-1-lets-get-started-fad78ec34dcf

Summary -

This is the first blog that I wrote for GSoC. Taylor
suggested that I should work on "integrating a lookup table
extension" first as it is smaller compared to other sub-projects.

The idea is to have a table at the end of .bitmap file which
will contain the offsets (and xor-offsets) of the bitmaps of
selected commits. Whenever git try to get the bitmap of a
particular commit, instead of loading each bitmaps one by one,
git will parse only the desired bitmap by using the offset and
xor-offset of the table. This will reduce the overhead of
loading each and every bitmap.
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