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ClickHouse® is a real-time analytics DBMS
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Previously it was possible to have a race while updating files_count/bytes_count, since INSERT updates it those counters from one thread and the same metrics are updated from filesystem in a separate thread, and even though the access is synchronized with the mutex it avoids the race only for accessing the variables not the logical race, since it is possible that getFiles() from a separate thread will increment counters and later addAndSchedule() will increment them again. Here you can find an example of this race [1]. [1]: https://pastila.nl/?00950e00/41a3c7bbb0a7e75bd3f2922c58b02334 Note, that I analyzed logs from production system with lots of async Distributed INSERT and everything is OK there, even though the logs contains the following: 2022.11.20 02:21:15.459483 [ 11528 ] {} <Trace> v21.dist_out.DirectoryMonitor: Files set to 35 (was 34) 2022.11.20 02:21:15.459515 [ 11528 ] {} <Trace> v21.dist_out.DirectoryMonitor: Bytes set to 4035418 (was 3929008) 2022.11.20 02:21:15.819488 [ 11528 ] {} <Trace> v21.dist_out.DirectoryMonitor: Files set to 1 (was 2) 2022.11.20 02:21:15.819502 [ 11528 ] {} <Trace> v21.dist_out.DirectoryMonitor: Bytes set to 190072 (was 296482) As you may see it first increases the counters and next update decreases (and 4035418-3929008 == 296482-190072) Refs: #23885 Reported-by: @tavplubix Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com> |
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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.
- ClickHouse Cloud ClickHouse as a service, built by the creators and maintainers.
- 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
- v22.11 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 Meetup at the Deutsche Bank office in Berlin Hear from Deutsche Bank on why they chose ClickHouse for big sensitive data in a regulated environment. The ClickHouse team will then present how ClickHouse is used for real time financial data analytics, including tick data, trade analytics and risk management.
- AWS re:Invent Core members of the ClickHouse team -- including 2 of our founders -- will be at re:Invent from November 29 to December 3. We are available on the show floor, but are also determining interest in holding an event during the time there.