Todd Lipcon has posted comments on this change. ( http://gerrit.cloudera.org:8080/15800 )
Change subject: KUDU-2844 (1/3): make BlockHandle ref-counted ...................................................................... Patch Set 2: (1 comment) http://gerrit.cloudera.org:8080/#/c/15800/2/src/kudu/cfile/block_handle.h File src/kudu/cfile/block_handle.h: http://gerrit.cloudera.org:8080/#/c/15800/2/src/kudu/cfile/block_handle.h@94 PS2, Line 94: boost::variant<BlockCacheHandle, std::shared_ptr<BlockHandle>> ref_; > Given how many block handlers we expect there to be in the lifespan of a se Since we use std::make_shared I think it ends up with the same single-allocation single-cacheline effect anyway. We should update the contribution guide. From a bit of reading, it seems like there is some memory footprint downside to shared_ptr instead of scoped_refptr: https://www.nextptr.com/tutorial/ta1358374985/shared_ptr-basics-and-internals-with-examples It seems the enable_shared_from_this<T> adds 16 bytes (a weak ptr) to the footprint of BlockHandle, and a shared_ptr control block is at least 16 bytes. The above doc claims it's 24 or 32 but at least with libstdcxx I'm only seeing 16 when I try it out. So, the total overhead is 32 bytes per BlockHandle, whereas with scoped_refptr it's only 8 bytes. What do you think, is it worth going back to scoped_refptr instead of std::shared_ptr? I guess we have one BlockHandle per initialized dictionary block, right? The rest should be transient. -- To view, visit http://gerrit.cloudera.org:8080/15800 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: kudu Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I1077fcc841ca31a2cb523769fffeed2d27782bc1 Gerrit-Change-Number: 15800 Gerrit-PatchSet: 2 Gerrit-Owner: Todd Lipcon <t...@apache.org> Gerrit-Reviewer: Alexey Serbin <aser...@cloudera.com> Gerrit-Reviewer: Andrew Wong <andrew.w...@cloudera.com> Gerrit-Reviewer: Andrew Wong <aw...@cloudera.com> Gerrit-Reviewer: Kudu Jenkins (120) Gerrit-Reviewer: Todd Lipcon <t...@apache.org> Gerrit-Reviewer: Volodymyr Verovkin <verjov...@cloudera.com> Gerrit-Comment-Date: Thu, 13 Aug 2020 20:28:48 +0000 Gerrit-HasComments: Yes
