BackgroundSchedulePool remove Poco::NotificationQueue

[kitaisreal]

Changelog category (leave one):

• Performance Improvement

BackgroundSchedulePool produce a lot of calls to wait with timeout for NotificationQueue. Such calls are also visible on flame graphs and for some benchmarks can take 15-20% of CPU time.

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

Fix excessive CPU usage in background when there are a lot of tables.

[kitaisreal]

@Mergifyio update

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[kitaisreal]

Query:

SELECT sum(WatchID) FROM hits_100m_obfuscated GROUP BY WatchID FORMAT Null;

Before:

After:

Background pool is BgSchPool.

[kitaisreal]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated