Add aggregation function for Largest-Triangle-Three-Buckets

[sinsinan]

Changelog category (leave one):

• New Feature

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

Added aggregation function lttb which uses the Largest-Triangle-Three-Buckets algorithm for downsampling data for visualization.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

[CLAassistant]

All committers have signed the CLA.

[robot-ch-test-poll4]

This is an automated comment for commit b3b2277 with description of existing statuses. It's updated for the latest CI running

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Successful checks

Check name	Description	Status
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Sqllogic	Run clickhouse on the sqllogic test set against sqlite and checks that all statements are passed	✅ success
Stateful tests	Runs stateful functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	✅ success
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Check name	Description	Status
Integration tests	The integration tests report. In parenthesis the package type is given, and in square brackets are the optional part/total tests	❌ failure
Stateless tests	Runs stateless functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	❌ failure
Stress test	Runs stateless functional tests concurrently from several clients to detect concurrency-related errors	❌ failure

[sinsinan]

@nickitat updated code according to report.

[sinsinan]

@nickitat can we test this ?

[sinsinan]

@nickitat I can see that it requires a can be tested label.

[sinsinan]

Hey @nickitat , it appears that the code is passing all tests except for one unrelated test case in the performance comparison. Could we review the code?

[sinsinan]

Hey @nickitat , it appears that the code is passing all tests except for one unrelated test case in the performance comparison. Could we review the code?

It'll probably pass if we retest this specific test https://github.com/ClickHouse/ClickHouse/actions/runs/5828437103/job/15815152543 .

[sinsinan]

@nickitat @alexey-milovidov , please review the changes

[sinsinan]

Hi @nickitat , it seems to be passing most of the test cases, failing ones doesn't seem to be related.

[sinsinan]

Hi @nickitat , @alexey-milovidov , can we merge this ?

[alexey-milovidov]

@nickitat is on vacation this week, he will review later.

[alexey-milovidov]

lttb does not sound like a good name.
Let's rename to largestTriangleThreeBuckets

[sinsinan]

Hi @nickitat , @alexey-milovidov , Just checking in on this PR. If any changes are needed, please let me know. Appreciate your time!

[UnamedRus]

IMO, it would be nice to have ttlb as alias for several reasons:

• largestTriangleThreeBuckets is too long.
• Other DBMS have this function named as ttlb

https://docs.timescale.com/api/latest/hyperfunctions/downsampling/#downsampling-functions

[nickitat]

let's add the alias UnamedRus suggested and merge

[sinsinan]

let's add the alias UnamedRus suggested and merge

@nickitat added alias, you can proceed to merge

[nickitat]

Stress test (ubsan) - #55041
Stress test (asan) - looks like we hang in sched_setaffinity

[alexey-milovidov]

@nickitat could you please take a look at #56762 ?