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https://github.com/ceph/ceph
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f904078344
This misspelling occurred twice in this document. Signed-off-by: Zac Dover <zac.dover@gmail.com>
285 lines
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285 lines
12 KiB
ReStructuredText
=======
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crimson
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=======
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Crimson is the code name of crimson-osd, which is the next generation ceph-osd.
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It targets fast networking devices, fast storage devices by leveraging state of
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the art technologies like DPDK and SPDK, for better performance. And it will
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keep the support of HDDs and low-end SSDs via BlueStore. Crimson will try to
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be backward compatible with classic OSD.
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.. highlight:: console
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Building Crimson
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================
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Crimson is not enabled by default. To enable it::
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$ WITH_SEASTAR=true ./install-deps.sh
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$ mkdir build && cd build
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$ cmake -DWITH_SEASTAR=ON ..
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Please note, `ASan`_ is enabled by default if crimson is built from a source
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cloned using git.
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Also, Seastar uses its own lockless allocator which does not play well with
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the alien threads. So, to use alienstore / bluestore backend, you might want to
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pass ``-DSeastar_CXX_FLAGS=-DSEASTAR_DEFAULT_ALLOCATOR`` to ``cmake`` when
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configuring this project to use the libc allocator, like::
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$ cmake -DWITH_SEASTAR=ON -DSeastar_CXX_FLAGS=-DSEASTAR_DEFAULT_ALLOCATOR ..
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.. _ASan: https://github.com/google/sanitizers/wiki/AddressSanitizer
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Running Crimson
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===============
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As you might expect, crimson is not featurewise on par with its predecessor yet.
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object store backend
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--------------------
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At the moment ``crimson-osd`` offers two object store backends:
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- CyanStore: CyanStore is modeled after memstore in classic OSD.
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- AlienStore: AlienStore is short for Alienized BlueStore.
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Seastore is still under active development.
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daemonize
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---------
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Unlike ``ceph-osd``, ``crimson-osd`` does daemonize itself even if the
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``daemonize`` option is enabled. Because, to read this option, ``crimson-osd``
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needs to ready its config sharded service, but this sharded service lives
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in the seastar reactor. If we fork a child process and exit the parent after
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starting the Seastar engine, that will leave us with a single thread which is
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the replica of the thread calls `fork()`_. This would unnecessarily complicate
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the code, if we would have tackled this problem in crimson.
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Since a lot of GNU/Linux distros are using systemd nowadays, which is able to
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daemonize the application, there is no need to daemonize by ourselves. For
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those who are using sysvinit, they can use ``start-stop-daemon`` for daemonizing
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``crimson-osd``. If this is not acceptable, we can whip up a helper utility
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to do the trick.
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.. _fork(): http://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html
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logging
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-------
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Currently, ``crimson-osd`` uses the logging utility offered by Seastar. see
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``src/common/dout.h`` for the mapping between different logging levels to
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the severity levels in Seastar. For instance, the messages sent to ``derr``
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will be printed using ``logger::error()``, and the messages with debug level
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over ``20`` will be printed using ``logger::trace()``.
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+---------+---------+
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| ceph | seastar |
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+---------+---------+
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| < 0 | error |
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+---------+---------+
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| 0 | warn |
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+---------+---------+
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| [1, 5) | info |
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+---------+---------+
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| [5, 20] | debug |
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+---------+---------+
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| > 20 | trace |
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+---------+---------+
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Please note, ``crimson-osd``
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does not send the logging message to specified ``log_file``. It writes
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the logging messages to stdout and/or syslog. Again, this behavior can be
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changed using ``--log-to-stdout`` and ``--log-to-syslog`` command line
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options. By default, ``log-to-stdout`` is enabled, and the latter disabled.
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vstart.sh
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---------
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To facilitate the development of crimson, following options would be handy when
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using ``vstart.sh``,
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``--crimson``
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start ``crimson-osd`` instead of ``ceph-osd``
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``--nodaemon``
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do not daemonize the service
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``--redirect-output``
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redirect the stdout and stderr of service to ``out/$type.$num.stdout``.
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``--osd-args``
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pass extra command line options to crimson-osd or ceph-osd. It's quite
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useful for passing Seastar options to crimson-osd. For instance, you could
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use ``--osd-args "--memory 2G"`` to set the memory to use. Please refer
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the output of::
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crimson-osd --help-seastar
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for more Seastar specific command line options.
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``--memstore``
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use the CyanStore as the object store backend.
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``--bluestore``
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use the AlienStore as the object store backend. This is the default setting,
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if not specified otherwise.
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So, a typical command to start a single-crimson-node cluster is::
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$ MGR=1 MON=1 OSD=1 MDS=0 RGW=0 ../src/vstart.sh -n -x \
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--without-dashboard --memstore \
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--crimson --nodaemon --redirect-output \
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--osd-args "--memory 4G"
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Where we assign 4 GiB memory, a single thread running on core-0 to crimson-osd.
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You could stop the vstart cluster using::
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$ ../src/stop.sh --crimson
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CBT Based Testing
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=================
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We can use `cbt`_ for performing perf tests::
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$ git checkout master
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$ make crimson-osd
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$ ../src/script/run-cbt.sh --cbt ~/dev/cbt -a /tmp/baseline ../src/test/crimson/cbt/radosbench_4K_read.yaml
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$ git checkout yet-another-pr
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$ make crimson-osd
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$ ../src/script/run-cbt.sh --cbt ~/dev/cbt -a /tmp/yap ../src/test/crimson/cbt/radosbench_4K_read.yaml
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$ ~/dev/cbt/compare.py -b /tmp/baseline -a /tmp/yap -v
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19:48:23 - INFO - cbt - prefill/gen8/0: bandwidth: (or (greater) (near 0.05)):: 0.183165/0.186155 => accepted
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19:48:23 - INFO - cbt - prefill/gen8/0: iops_avg: (or (greater) (near 0.05)):: 46.0/47.0 => accepted
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19:48:23 - WARNING - cbt - prefill/gen8/0: iops_stddev: (or (less) (near 0.05)):: 10.4403/6.65833 => rejected
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19:48:23 - INFO - cbt - prefill/gen8/0: latency_avg: (or (less) (near 0.05)):: 0.340868/0.333712 => accepted
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19:48:23 - INFO - cbt - prefill/gen8/1: bandwidth: (or (greater) (near 0.05)):: 0.190447/0.177619 => accepted
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19:48:23 - INFO - cbt - prefill/gen8/1: iops_avg: (or (greater) (near 0.05)):: 48.0/45.0 => accepted
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19:48:23 - INFO - cbt - prefill/gen8/1: iops_stddev: (or (less) (near 0.05)):: 6.1101/9.81495 => accepted
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19:48:23 - INFO - cbt - prefill/gen8/1: latency_avg: (or (less) (near 0.05)):: 0.325163/0.350251 => accepted
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19:48:23 - INFO - cbt - seq/gen8/0: bandwidth: (or (greater) (near 0.05)):: 1.24654/1.22336 => accepted
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19:48:23 - INFO - cbt - seq/gen8/0: iops_avg: (or (greater) (near 0.05)):: 319.0/313.0 => accepted
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19:48:23 - INFO - cbt - seq/gen8/0: iops_stddev: (or (less) (near 0.05)):: 0.0/0.0 => accepted
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19:48:23 - INFO - cbt - seq/gen8/0: latency_avg: (or (less) (near 0.05)):: 0.0497733/0.0509029 => accepted
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19:48:23 - INFO - cbt - seq/gen8/1: bandwidth: (or (greater) (near 0.05)):: 1.22717/1.11372 => accepted
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19:48:23 - INFO - cbt - seq/gen8/1: iops_avg: (or (greater) (near 0.05)):: 314.0/285.0 => accepted
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19:48:23 - INFO - cbt - seq/gen8/1: iops_stddev: (or (less) (near 0.05)):: 0.0/0.0 => accepted
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19:48:23 - INFO - cbt - seq/gen8/1: latency_avg: (or (less) (near 0.05)):: 0.0508262/0.0557337 => accepted
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19:48:23 - WARNING - cbt - 1 tests failed out of 16
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Where we compile and run the same test against two branches. One is ``master``, another is ``yet-another-pr`` branch.
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And then we compare the test results. Along with every test case, a set of rules is defined to check if we have
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performance regressions when comparing two set of test results. If a possible regression is found, the rule and
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corresponding test results are highlighted.
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.. _cbt: https://github.com/ceph/cbt
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Hacking Crimson
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===============
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Seastar Documents
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-----------------
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See `Seastar Tutorial <https://github.com/scylladb/seastar/blob/master/doc/tutorial.md>`_ .
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Or build a browsable version and start an HTTP server::
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$ cd seastar
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$ ./configure.py --mode debug
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$ ninja -C build/debug docs
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$ python3 -m http.server -d build/debug/doc/html
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You might want to install ``pandoc`` and other dependencies beforehand.
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Debugging Crimson
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=================
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Debugging with GDB
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------------------
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The `tips`_ for debugging Scylla also apply to Crimson.
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.. _tips: https://github.com/scylladb/scylla/blob/master/docs/debugging.md#tips-and-tricks
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Human-readable backtraces with addr2line
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----------------------------------------
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When a seastar application crashes, it leaves us with a serial of addresses, like::
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Segmentation fault.
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Backtrace:
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0x00000000108254aa
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0x00000000107f74b9
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0x00000000105366cc
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0x000000001053682c
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0x00000000105d2c2e
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0x0000000010629b96
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0x0000000010629c31
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0x00002a02ebd8272f
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0x00000000105d93ee
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0x00000000103eff59
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0x000000000d9c1d0a
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/lib/x86_64-linux-gnu/libc.so.6+0x000000000002409a
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0x000000000d833ac9
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Segmentation fault
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``seastar-addr2line`` offered by Seastar can be used to decipher these
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addresses. After running the script, it will be waiting for input from stdin,
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so we need to copy and paste the above addresses, then send the EOF by inputting
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``control-D`` in the terminal::
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$ ../src/seastar/scripts/seastar-addr2line -e bin/crimson-osd
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0x00000000108254aa
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0x00000000107f74b9
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0x00000000105366cc
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0x000000001053682c
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0x00000000105d2c2e
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0x0000000010629b96
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0x0000000010629c31
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0x00002a02ebd8272f
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0x00000000105d93ee
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0x00000000103eff59
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0x000000000d9c1d0a
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0x00000000108254aa
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[Backtrace #0]
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seastar::backtrace_buffer::append_backtrace() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1136
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seastar::print_with_backtrace(seastar::backtrace_buffer&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1157
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seastar::print_with_backtrace(char const*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1164
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seastar::sigsegv_action() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5119
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seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::operator()(int, siginfo_t*, void*) const at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5105
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seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::_FUN(int, siginfo_t*, void*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5101
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?? ??:0
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seastar::smp::configure(boost::program_options::variables_map, seastar::reactor_config) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5418
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seastar::app_template::run_deprecated(int, char**, std::function<void ()>&&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/app-template.cc:173 (discriminator 5)
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main at /home/kefu/dev/ceph/build/../src/crimson/osd/main.cc:131 (discriminator 1)
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Please note, ``seastar-addr2line`` is able to extract the addresses from
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the input, so you can also paste the log messages like::
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2020-07-22T11:37:04.500 INFO:teuthology.orchestra.run.smithi061.stderr:Backtrace:
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2020-07-22T11:37:04.500 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e78dbc
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2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e7f0
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2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e8b8
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2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: 0x0000000000e3e985
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2020-07-22T11:37:04.501 INFO:teuthology.orchestra.run.smithi061.stderr: /lib64/libpthread.so.0+0x0000000000012dbf
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Unlike classic OSD, crimson does not print a human-readable backtrace when it
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handles fatal signals like `SIGSEGV` or `SIGABRT`. And it is more complicated
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when it comes to a stripped binary. So before planting a signal handler for
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those signals in crimson, we could to use `script/ceph-debug-docker.sh` to parse
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the addresses in the backtrace::
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# assuming you are under the source tree of ceph
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$ ./src/script/ceph-debug-docker.sh --flavor crimson master:27e237c137c330ebb82627166927b7681b20d0aa centos:8
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....
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[root@3deb50a8ad51 ~]# wget -q https://raw.githubusercontent.com/scylladb/seastar/master/scripts/seastar-addr2line
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[root@3deb50a8ad51 ~]# dnf install -q -y file
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[root@3deb50a8ad51 ~]# python3 seastar-addr2line -e /usr/bin/crimson-osd
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# paste the backtrace here
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