Ashwani Raina has posted comments on this change. ( http://gerrit.cloudera.org:8080/24412 )
Change subject: KUDU-3429 Add extensive test for delta generation (3/n) ...................................................................... Patch Set 4: (1 comment) http://gerrit.cloudera.org:8080/#/c/24412/4/src/kudu/tablet/compaction-highmem-test.cc File src/kudu/tablet/compaction-highmem-test.cc: http://gerrit.cloudera.org:8080/#/c/24412/4/src/kudu/tablet/compaction-highmem-test.cc@326 PS4, Line 326: kLargePayload[i] = static_cast<char>((i * 193U + 37U) % 251U); > +1 for using STL-based random generators if it works here as expected The reason for using periodic variant is to have periodic repetition of 251-byte blocks in a 64K buffer. However, std::mt19937 yields totally non-periodic output that is not compressible. The goal here is to achieve 'compressible-on-disk & expands-in-memory' kind of deal as well as little randomness to have default compaction memory budget able to accommodate the undo deltas. If std::mt199337 is used, on-disk undo size has to be very high if we want to hit a 'good' peak_memory_usage because compression would be ineffective for it and the undo data size on-disk is going to be near close to the peak memory use by rowset compaction. Also, to make on-disk size high, default compaction budget configuration also needs to be changed in the test. If a constant pattern (all-same byte) is used, although it has smaller on-disk footprint there would be increased CPU time which means increased test run time. Partial pseudo-random with periodic repetition is a middle ground with best of both the worlds. I noticed how a certain level of inaccuracy in the comments above could cause confusion. Made changes there to keep it simple and clear. -- To view, visit http://gerrit.cloudera.org:8080/24412 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: kudu Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I8c337dba87a9d1cf549f9b53813da8d50e86b6b4 Gerrit-Change-Number: 24412 Gerrit-PatchSet: 4 Gerrit-Owner: Ashwani Raina <[email protected]> Gerrit-Reviewer: Abhishek Chennaka <[email protected]> Gerrit-Reviewer: Alexey Serbin <[email protected]> Gerrit-Reviewer: Ashwani Raina <[email protected]> Gerrit-Reviewer: Kudu Jenkins (120) Gerrit-Reviewer: Marton Greber <[email protected]> Gerrit-Reviewer: Zoltan Martonka <[email protected]> Gerrit-Comment-Date: Tue, 04 Aug 2026 13:51:45 +0000 Gerrit-HasComments: Yes
