Investigate whether param estimator is affected by disk caching

[MaksymZavershynskyi]

As reported by @SkidanovAlex Ubuntu can cache up to 1GiB of disk, we need to make sure param estimator is hitting the actual disk and not the cache.

[bowenwang1996]

@olonho what is the status of this issue?

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[bowenwang1996]

@matklad @olonho

[matklad]

No progress here, good to keep in mind though. #4771 feels related as vaguely database-related issue which

[stale]

This issue has been automatically marked as stale because it has not had recent activity in the last 2 months.
It will be closed in 7 days if no further activity occurs.
Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity in the last 2 months.
It will be closed in 7 days if no further activity occurs.
Thank you for your contributions.

[jakmeier]

Closing this since we merged #6347.

Summary: Yes we are affected by disk caching. We can get around it now by adding --drop-os-cache but it requires root. Long-term plan is to have a more separate IO estimation step but for the moment this is good enough to get estimations that are not affected by disk cache.