Hello developers, this is the thread where you can know about my weekly GSoC blog links. My Project - Reachability bitmap improvements Blog update ------------ Title - GSoC Week 6: using CRoaring library Blog link - https://medium.com/@abhra303/gsoc-week-6-using-croaring-library-be309cfa89f5 Summary - I missed the week 5 blog update. So this blog covers both week 5 and week 6 work updates. I submitted my latest version Of `lookup-table-extension` patch series. There are some issues with CRoaring e.g. it do not store in network byte order (which I confirmed in Roaringbitmap's google group[1]). So, I need to make some changes to fix it. I have already finished implementing `roaring_portable_network_serialize` and `..._deserialize`. My next step is to use its functions in Git's codebase. I will submit the patch series soon. Previous blogs --------------- ------------------------------------------------------- Title - GSoC Week 4: diving into roaring bitmaps Blog link - https://medium.com/@abhra303/gsoc-week-4-diving-into-roaring-bitmaps-f028f931d873 Summary - I am thinking of submitting a patch to explain the workings of bitmaps. I will be creating a new file 'technical/reachability- bitmaps.txt` for that. This week I spent my time on diving more into Croaring[1]. I tried to understand how they work internally, the available functions they offer, their serializing format etc. The serialisation format[2] seems fine to me but still I want to know Kaartic and Taylor’s opinions. Another thing I noticed here is that each roaring bitmaps are designed to store sets of 32-bit (unsigned) integers. Thus a Roaring bitmap can contain up to 4294967296 integers. I am not sure if this is sufficient for us. My next step is to make the new bitmap format version 2(with roaring bitmaps) and modify rest of the code so that those code can accept the new bitmap format version. ------------------------------------------------------- Title - GSoC Week 3: working on further improvements Blog link - https://medium.com/@abhra303/gsoc-week-3-working-on-further-improvements-13a27db64cd5 Summary - In this week, I continued to work on further improvements of The bitmap-lookup-table patch series. Some of the requested changes are (1) Improve the documentation and fix typos (2) add comments (3) Disable `pack.writeBitmapLookupTable` by default (4) Fix alignment issues (5) Make a `bitmap_lookup_table_triple` struct (6) Subtract the table_size from index_end irrespective of the value of GIT_TEST_READ_COMMIT_TABLE. After implementing all the requested changes, I started working on the idea I mentioned in my previous blog as my next step. The idea is to stop the xor stack filling loop if the current xor bitmap is already stored and assign `xor_bitmap` to it. As this bitmap is already stored, we don't need to iterate further as we know all the other bitmaps that are needed to parse this bitmap has already been stored. My next step is to roughly implement roaring run bitmaps and run performance tests to check if it's really worth it. ------------------------------------------------------- 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. ------------------------------------------------------- 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. -------------------------------------------------------
