Add test for last written lsn cache

[knizhnik]

Main:

test_measure_read_latency_heavy_write_workload[neon-1].run_duration: 29.455 s
test_measure_read_latency_heavy_write_workload[neon-1].read_latency_avg: 4.346 s
test_measure_read_latency_heavy_write_workload[neon-1].read_latency_stdev: 5.499 s

last_written_lsn_cache:

test_measure_read_latency_heavy_write_workload[neon-1].run_duration: 34.074 s
test_measure_read_latency_heavy_write_workload[neon-1].read_latency_avg: 0.422 s
test_measure_read_latency_heavy_write_workload[neon-1].read_latency_stdev: 0.761 s

[aome510]

Look like this branch is based on the code in #1891 as record_read_latency isn't defined anywhere in main.

The new test shares some similarities with the tests added in #1891. I think we can use tests in #1891 to test the last_written_lsn_cache implementation instead.

Also, looks like CircleCI doesn't run because "We have detected an anomaly that violates the CircleCI Terms of Service. Troubleshoot", which is probably because the PR is submitted from Russia.

[hlinnaka]

Can you separate the test changes and the code changes into two commits, and push them separately, please? That way, we'll get "before" and "after" measurements from the CI.

[knizhnik]

Can you separate the test changes and the code changes into two commits, and push them separately, please? That way, we'll get "before" and "after" measurements from the CI.

Do you mean create separate PR for tests or just add tests in separate commit within this PR?
But in the last case I afraid that "squash and marge" will still group them in one commit...

[hlinnaka]

Can you separate the test changes and the code changes into two commits, and push them separately, please? That way, we'll get "before" and "after" measurements from the CI.

Do you mean create separate PR for tests or just add tests in separate commit within this PR? But in the last case I afraid that "squash and marge" will still group them in one commit...

You can use squash them into two commits on your laptop with "git rebase -i origin/master", and force push to the branch to update the PR. After the CI passes, you can do a regular push from your laptop with "git push origin last_written_lsn_cache:main".

Hmm. Not sure the CI would run on 'main' separately for the two commits if you do that though. So two separate PRs is probably the easiest way to do it.

[knizhnik]

Can you separate the test changes and the code changes into two commits, and push them separately, please? That way, we'll get "before" and "after" measurements from the CI.

Do you mean create separate PR for tests or just add tests in separate commit within this PR? But in the last case I afraid that "squash and marge" will still group them in one commit...

You can use squash them into two commits on your laptop with "git rebase -i origin/master", and force push to the branch to update the PR. After the CI passes, you can do a regular push from your laptop with "git push origin last_written_lsn_cache:main".

Hmm. Not sure the CI would run on 'main' separately for the two commits if you do that though. So two separate PRs is probably the easiest way to do it.

I have merged PR with tests and rebased this PR.
But to be able to merge it I need your approval for its postgres repository part:
neondatabase/postgres#201