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Disable system.kafka_consumers by default (due to possible live memory leak)#57822

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azat:kafka-disable-stat
Dec 14, 2023
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Disable system.kafka_consumers by default (due to possible live memory leak)#57822
alexey-milovidov merged 1 commit intoClickHouse:masterfrom
azat:kafka-disable-stat

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@azat azat commented Dec 13, 2023

Changelog category (leave one):

  • Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Disable system.kafka_consumers by default (due to possible live memory leak)

It is not safe to use statistics because of how KafkaEngine works - it pre-creates consumers, and this leads to the situation when this statistics entries generated (RD_KAFKA_OP_STATS), but never consumed.

Which creates a live memory leak for a server with Kafka tables, but without materialized view attached to it (and no SELECT).

Another problem is that this makes shutdown very slow, because of how pending queue entries are handled in librdkafka, it uses TAILQ_INSERT_SORTED, which is sorted insert into linked list, which works incredibly slow (likely you will never wait till it ends and kill the server)

For instance in my production setup the server was running for ~67 days with such table, and it got 1'942'233 TAILQ_INSERT_SORTED entries (which perfectly matches by the way - 67*86400/3 = 1'929'600), and it moved only 289'806 entries for a few hours, though I'm not sure how much time the process was in the running state, since most of the time it was with debugger attached.

So for now let's disable it, to make this patch easy for backporting, and I will think about long term fix - do not pre-create consumers in Kafka engine.

Fixes: #50999 (cc @ilejn)

@azat
Disable system.kafka_consumers by default (due to possible live memor…
055c231 
…y leak)

It is not safe to use statistics because of how KafkaEngine works - it
pre-creates consumers, and this leads to the situation when this
statistics entries generated (RD_KAFKA_OP_STATS), but never consumed.

Which creates a live memory leak for a server with Kafka tables, but
without materialized view attached to it (and no SELECT).

Another problem is that this makes shutdown very slow, because of how
pending queue entries are handled in librdkafka, it uses
TAILQ_INSERT_SORTED, which is sorted insert into linked list, which
works incredibly slow (likely you will never wait till it ends and kill
the server)

For instance in my production setup the server was running for ~67 days
with such table, and it got 1'942'233 `TAILQ_INSERT_SORTED` entries
(which perfectly matches by the way - `67*86400/3` = 1'929'600), and it
moved only 289'806 entries for a few hours, though I'm not sure how much
time the process was in the running state, since most of the time it was
with debugger attached.

So for now let's disable it, to make this patch easy for backporting,
and I will think about long term fix - do not pre-create consumers in
Kafka engine.

Signed-off-by: Azat Khuzhin <[email protected]>
@robot-clickhouse robot-clickhouse added the pr-bugfix Pull request with bugfix, not backported by default label Dec 13, 2023
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robot-clickhouse commented Dec 13, 2023 •
edited by robot-ch-test-poll4
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@azat azat mentioned this pull request Dec 13, 2023
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ilejn commented Dec 13, 2023

Hm ... sorry to hear that it caused so many troubles.
Thanks for the insights,
we'll definitely try to fix these issues.

@azat azat mentioned this pull request Dec 13, 2023
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azat commented Dec 13, 2023

we'll definitely try to fix these issues.

Here is a fix - #57829

@alexey-milovidov alexey-milovidov self-assigned this Dec 14, 2023
@alexey-milovidov alexey-milovidov merged commit 7a2edb4 into ClickHouse:master Dec 14, 2023
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alexey-milovidov commented Dec 14, 2023

@azat, it is much better to remove the feature entirely than disabling it.

@azat azat deleted the kafka-disable-stat branch December 14, 2023 08:09
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azat commented Dec 14, 2023

it is much better to remove the feature entirely than disabling it.

@alexey-milovidov I think that this information can be useful, and I've already submitted a proper fix.
And I've submitted a workaround and a proper fix separately since "proper fix" is not that trivial, and backporting it is a bad idea.

And also let's backport this patch.

@SaltTan SaltTan mentioned this pull request Dec 15, 2023
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chiragb1994 commented Dec 16, 2023

Will this fix be backported to v23.8?

@Enmk Enmk mentioned this pull request Dec 21, 2023
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Enmk pushed a commit to Altinity/ClickHouse that referenced this pull request Dec 22, 2023
@alexey-milovidov @Enmk
Merge pull request ClickHouse#57822 from azat/kafka-disable-stat
ecd52ec 
Disable system.kafka_consumers by default (due to possible live memory leak)
Enmk added a commit to Altinity/ClickHouse that referenced this pull request Dec 22, 2023
@Enmk
Merge pull request #346 from Altinity/backport/23.8/57822_disable_sys…
37e99eb 
…tem_kafka_consumers_table

23.8 Backport of ClickHouse#57822 - Disable `system.kafka_consumers` by default
@Enmk Enmk mentioned this pull request Dec 26, 2023
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azat commented Dec 27, 2023

@alexey-milovidov objections on backporting this patch?

@alexey-milovidov alexey-milovidov added the pr-must-backport Pull request should be backported intentionally. Use this label with great care! label Dec 27, 2023
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robot-clickhouse added a commit that referenced this pull request Dec 27, 2023
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Backport #57822 to 23.8: Disable system.kafka_consumers by default (d…
2248b77 
…ue to possible live memory leak)
@robot-ch-test-poll2 robot-ch-test-poll2 mentioned this pull request Dec 27, 2023
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@robot-ch-test-poll2 robot-ch-test-poll2 mentioned this pull request Dec 27, 2023
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robot-clickhouse added a commit that referenced this pull request Dec 27, 2023
@robot-clickhouse
Backport #57822 to 23.9: Disable system.kafka_consumers by default (d…
631d6ce 
…ue to possible live memory leak)
@robot-ch-test-poll2 robot-ch-test-poll2 mentioned this pull request Dec 27, 2023
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@robot-ch-test-poll2 robot-ch-test-poll2 mentioned this pull request Dec 27, 2023
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Backport #57822 to 23.10: Disable system.kafka_consumers by default (…
8881fb6 
…due to possible live memory leak)
@robot-ch-test-poll2 robot-ch-test-poll2 mentioned this pull request Dec 27, 2023
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robot-clickhouse added a commit that referenced this pull request Dec 27, 2023
@robot-clickhouse
Backport #57822 to 23.11: Disable system.kafka_consumers by default (…
eda971b 
…due to possible live memory leak)
alexey-milovidov added a commit that referenced this pull request Dec 27, 2023
@alexey-milovidov
Merge pull request #58256 from ClickHouse/backport/23.8/57822
8506171 
Backport #57822 to 23.8: Disable system.kafka_consumers by default (due to possible live memory leak)
alexey-milovidov added a commit that referenced this pull request Dec 27, 2023
@alexey-milovidov
Merge pull request #58258 from ClickHouse/backport/23.9/57822
8f7c19f 
Backport #57822 to 23.9: Disable system.kafka_consumers by default (due to possible live memory leak)
alexey-milovidov added a commit that referenced this pull request Dec 27, 2023
@alexey-milovidov
Merge pull request #58260 from ClickHouse/backport/23.10/57822
8262b27 
Backport #57822 to 23.10: Disable system.kafka_consumers by default (due to possible live memory leak)
alexey-milovidov added a commit that referenced this pull request Dec 27, 2023
@alexey-milovidov
Merge pull request #58262 from ClickHouse/backport/23.11/57822
ae8e288 
Backport #57822 to 23.11: Disable system.kafka_consumers by default (due to possible live memory leak)
@robot-ch-test-poll2 robot-ch-test-poll2 added the pr-backports-created Backport PRs are successfully created, it won't be processed by CI script anymore label Dec 28, 2023
@alexey-milovidov alexey-milovidov mentioned this pull request Feb 25, 2024
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@azat @robot-clickhouse @ilejn @alexey-milovidov @chiragb1994 @robot-ch-test-poll2