From: Abhradeep Chakraborty <chakrabortyabhradeep79@xxxxxxxxx> 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 9: finding the fix of the failing test case Blog link - https://medium.com/@abhra303/gsoc-week-9-finding-the-fix-of-the-failing-test-case-30bc623cb4c Summary - This week I put most of the time on finding the root cause of a test failure. I took my roaring bitmap integration a little further. I decided to use Chunk-format API for the new `.bitmap` version. As midx also uses Chunk format, we can maintain uniformity in designing file format. I tried various ways to find the root cause but till now I am not able to do so. I need to investigate further because I have to be sure whether Calling `oe_map_new_pack()` function is causing the failure. As my exam is starting from 18 Aug, I can't spend much time here. But I think we are very near to solve the issue :) Previous blogs --------------- ------------------------------------------------------- Title - GSoC Week 7: improving Performance tests Blog link - https://medium.com/@abhra303/gsoc-week-7-improving-performance-tests-ea9bfa180775 Summary - In this week I work further on Git specific CRoaring fixtures. Besides, there were another round of review on my bitmap-lookup-table patch series. For now I wrote all Git specific functions in roaring.c functions. As Taylor told me — we first need to check whether roaring bitmaps really create an impact in performance. With these functions roaring bitmaps can now be stored in network byte order which means it can work in big-endian systems also. Performance tests that I wrote previously were not accurate. Because the second call to test_bitmap is always working on the previously repacked repo, causing the the performance of the second call much faster than the previous one. My solution is to create a new file for each cases (i.e. with lookup table enabled and with lookup table disabled). There is another problem which is mysterious in nature. A test case under `t5327-multi-pack-bitmaps.sh` (and under `t5327-multi-pack-bitmaps-rev.sh` is failing when `GIT_TEST_DEFAULT_HASH=sha256`. It is passing in every other scenario. I found that this issue is related to the test script itself (and not related to the implementation code). I didn't get enough time to look into it though. I hope that I will be able to figure out the problem soon. ------------------------------------------------------- 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. ------------------------------------------------------- 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. -------------------------------------------------------
