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ClickHouse® is a real-time analytics DBMS
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This should significantly reduce the MemoryTracking drift, test shows that there is 0 drift after query storm (100 queries, via http/tcp/tcp in one session). TL;DR; To track memory, clickhouse creates memory tracker object for each thread **explicitly**, but until it is not created the memory allocations are not under account. There should not be lot of allocations w/o memory tracker, since most of the time it is created early enough, but even this maybe enough to trigger some problems. Plus sometimes it is not possible to create it, for example some 3d party library does not allow to do this explicitly: - for example before #15740 allocations from librdkafka threads, - or even worse, poco threads, they don't have any routines to do this. This won't be a problem for `MemoryTracking` metric if the deallocation will be done from the same thread w/o memory tracker (or vise versa), but this is not always true. NOTE, that this will slow down per-thread allocations w/o memory tracker, since before this patch there were no memory tracking for them while now they will be accounted in total_memory_tracker, and for total_memory_tracker max_untracked_memory is always reached. But this should not be significant. |
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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 quick high-level overview of ClickHouse on main page.
- Tutorial shows how to set up and query 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 to chat with ClickHouse users in real-time.
- Blog contains various ClickHouse-related articles, as well as announcements and reports about events.
- Code Browser with syntax highlight and navigation.
- Yandex.Messenger channel shares announcements and useful links in Russian.
- Contacts can help to get your questions answered if there are any.
- You can also fill this form to meet Yandex ClickHouse team in person.
Upcoming Events
- ClickHouse virtual office hours on October 22, 2020.