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ClickHouse® is a real-time analytics DBMS
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Azat Khuzhin 64b44be513 Account any IO that is done from ThreadPoolReader 
In case of some issues with the disk it is possible that
preadv2(RWF_NOWAIT)==EAGAIN can take a lot of time, so let's measure
even this case.

I've verified with a simple (almost) loop of preadv2(RWF_NOWAIT), and
got this:

    EAGAIN: 8565670 (out of 17148317)
    EAGAIN: 8565670 (out of 17148317)
    EAGAIN: 8565670 (out of 17148317)
    too long at offset=8691694, ret=18446744073709551615 (14.5016)
    too long at offset=8694766, ret=18446744073709551615 (14.4338)
    too long at offset=8694766, ret=18446744073709551615 (16.2144)

So here you can see that preadv2(RWF_NOWAIT) took 14-16 seconds in case
of failure.

Complete code can be found here [1].

  [1]: https://gist.github.com/azat/f4a6b0750316c42bec021064e0a7627c

I came up with this patch because I saw some stranginess in
ProfileEvents, that does not show all the time that was spend in IO when
pread_threadpool method was used.
Also there was some stranginess with trace_log too.

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>
2022-09-18 10:05:21 +02:00
.github Remove trash error message from integration tests 2022-09-17 20:24:56 +02:00
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contrib Merge pull request #41094 from HarryLeeIBM/hlee-s390x-zlib-ng 2022-09-18 07:55:20 +03:00
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docs Merge pull request #41214 from arenadata/ADQM-528-B 2022-09-17 19:25:11 +02:00
packages Update clickhouse-server.init 2022-09-13 20:54:56 -03:00
programs Merge branch 'master' into forbid-dlopen-2 2022-09-18 02:20:22 +02:00
src Account any IO that is done from ThreadPoolReader 2022-09-18 10:05:21 +02:00
tests Merge pull request #41450 from ClickHouse/remove-s3-sample-block-cache 2022-09-18 09:44:07 +03:00
utils Merge pull request #41287 from ClickHouse/DanRoscigno-patch-2 2022-09-14 16:50:02 -04:00
website move-images-to-clickhouse-presentations 2022-08-10 04:04:56 +02:00
.clang-format add BeforeLambdaBody to .clang-format 2022-02-11 16:51:45 +01:00
.clang-tidy Fix clang-tidy warnings (from clang-15) 2022-09-10 21:38:35 +02:00
.editorconfig Changed tabs to spaces in editor configs and in style guide [#CLICKHOUSE-3]. 2017-04-01 11:35:09 +03:00
.git-blame-ignore-revs Add files with revision to ignore for git blame 2022-09-13 23:05:56 +02:00
.gitattributes mark test data as binary 2022-01-22 03:19:47 +03:00
.gitignore feat: implement catboost in library-bridge 2022-09-08 09:01:32 +00:00
.gitmodules Revert "Add Annoy index" 2022-08-30 15:10:10 +03:00
.pylintrc Cover deprecated bad-* pylint options with black 2022-06-08 14:18:28 +02:00
.vimrc Changed tabs to spaces in editor configs and in style guide [#CLICKHOUSE-3]. 2017-04-01 11:35:09 +03:00
.yamllint Drop truthy.check-keys from yamllint (does not supported on CI) 2021-02-21 06:15:36 +03:00
AUTHORS Update AUTHORS 2021-09-22 11:38:03 +03:00
CHANGELOG.md Update CHANGELOG.md 2022-08-24 03:35:51 +03:00
CMakeLists.txt Fix debug symbols (Add a quirk to force clang emit .debug_aranges with ThinLTO) 2022-09-02 23:22:25 +02:00
CODE_OF_CONDUCT.md Add minimal code of conduct #9676 2020-03-16 12:44:28 +03:00
CONTRIBUTING.md Mention ClickHouse CLA in CONTRIBUTING.md (#32697) 2021-12-14 03:47:19 +03:00
format_sources allow several <graphite> targets (#603) 2017-03-21 23:08:09 +04:00
LICENSE Update year 2022-01-27 01:01:27 +03:00
PreLoad.cmake Update PreLoad.cmake 2022-08-26 18:30:05 +08:00
README.md Update README.md (#41091) 2022-09-07 20:58:36 +02:00
SECURITY.md Update security 2022-08-20 13:04:01 +02:00

README.md

ClickHouse — open source distributed column-oriented DBMS

ClickHouse® is an open-source column-oriented database management system that allows generating analytical data reports in real-time.

Useful Links

  • Official website has a quick high-level overview of ClickHouse on the main page.
  • Tutorial shows how to set up and query a small ClickHouse cluster.
  • Documentation provides more in-depth information.
  • YouTube channel has a lot of content about ClickHouse in video format.
  • Slack and Telegram allow chatting with ClickHouse users in real-time.
  • Blog contains various ClickHouse-related articles, as well as announcements and reports about events.
  • Code Browser (Woboq) with syntax highlight and navigation.
  • Code Browser (github.dev) with syntax highlight, powered by github.dev.
  • Contacts can help to get your questions answered if there are any.

Upcoming events

  • v22.9 Release Webinar Original creator, co-founder, and CTO of ClickHouse Alexey Milovidov will walk us through the highlights of the release, provide live demos, and share vision into what is coming in the roadmap.
  • ClickHouse for Analytics @ Barracuda Networks Join us for this in person meetup hosted by our friends at Barracuda in Bay Area.