[Bug 1894453] Re: Building Ceph packages with RelWithDebInfo

[Ponnuvel Palaniyappan]

An update:

I have built rocksdb with & without RelWithDebInfo. Some differences
are:

 - the exact set of additional flags used with RelWithDebInfo are: -O2
-NDEBUG -fno-omit-frame-pointer -momit-leaf-frame-pointer.

 - the size of rocksdb shared library (librocksdb.so): default-build =
156M, with-RelWithDebInfo = 235M (In the case of Ceph binaries, this
shared library isn't used separately but compiled into ceph-osd and
others. Similar comparison of ceph-osd binary size stripped: default-
build = 16M, with-RelWithDebInfo = 25M).

- There are about ~5700 asserts in rocksdb which would disappear with
RelWithDebInfo.


I am doing further performance benchmarks between the two versions and will update once done.

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https://bugs.launchpad.net/bugs/1894453

Title:
  Building Ceph packages with RelWithDebInfo

Status in ceph package in Ubuntu:
  In Progress

Bug description:
  This is to consider/discuss the possibility of whether the Ceph
  packages (UCA) should be built with RelWithDebInfo build option
  (CMAKE_BUILD_TYPE [0]) which can be supplied to the build script
  do_cmake.sh [1].

  Currently, Upstream as well as UCA builds default to 'Debug' [0]
  builds. But is any reason why shouldn't go for RelWithDebInfo (i.e.
  "Release with Debug information")?

  
  There's one issue noted with RelWithDebInfo which has a workaround too [2].

  In general, gcc's -O2 [3] build should generate better code as well as
  there's a specific case for Ceph [4] that it improves performance.

  [0] https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html

  [1] https://github.com/ceph/ceph/blob/master/do_cmake.sh

  [2] https://docs.ceph.com/docs/master/dev/perf/#common-issues

  [3] https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

  [4] https://bugs.gentoo.org/show_bug.cgi?id=733316

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