Add sql text counts stats to vtcombo,vtgate+vttablet

[timvaillancourt]

Description

This PR adds stats for the size of query text processed by vtgate and vttablet

This is useful to understand large queries that potentially cause performance, grpc message size, bandwidth problems

Related Issue(s)

Resolves #15929

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[timvaillancourt]

Opened this one with a lot of failing CI to see if others have ideas how to debug

The failures are confusing and feel unrelated to this change 🤔

[harshit-gangal]

Opened this one with a lot of failing CI to see if others have ideas how to debug

The failures are confusing and feel unrelated to this change 🤔

There failures are related to the changes made. I have pushed a commit that fixes some of those. You should run the test locally and fix the remaining if any.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.22%. Comparing base (0353ad4) to head (0531ce1).
Report is 59 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15897      +/-   ##
==========================================
- Coverage   68.45%   68.22%   -0.24%     
==========================================
  Files        1559     1541      -18     
  Lines      196825   197330     +505     
==========================================
- Hits       134736   134627     -109     
- Misses      62089    62703     +614     

☔ View full report in Codecov by Sentry.
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[timvaillancourt]

Opened this one with a lot of failing CI to see if others have ideas how to debug
The failures are confusing and feel unrelated to this change 🤔

There failures are related to the changes made. I have pushed a commit that fixes some of those.

@harshit-gangal indeed it is, thanks! 🤦 🙇

You should run the test locally and fix the remaining if any.

Good point, I've made a bad habit of relying on GitHub Actions CI because many go test CIs fail on my MacBook when they rely on external things (perhaps not this test). I'll give running CI locally another shot 👀

Somehow this was not obvious from the CI outputs I looked at, including this Unit test run that ends in just:

+ go-junit-report -set-exit-code
make: *** [Makefile:209: unit_test] Error 1
Error: Process completed with exit code 1.

Perhaps it's just the v15 fork/release I'm working on, but I'm used to the Unit test CI including the output of go test -v to help explain the failure. I'll see if something about that changed and if there is an alternative

[harshit-gangal]

Perhaps it's just the v15 fork/release I'm working on, but I'm used to the Unit test CI including the output of go test -v to help explain the failure. I'll see if something about that changed and if there is an alternative

The first step records the output, if you click on the step below in the CI you will see the output.

[harshit-gangal]

[timvaillancourt]

Perhaps it's just the v15 fork/release I'm working on, but I'm used to the Unit test CI including the output of go test -v to help explain the failure. I'll see if something about that changed and if there is an alternative

The first step records the output, if you click on the step below in the CI you will see the output.

@harshit-gangal ahh, that's where it goes! Thanks a lot more on this one soon

[shlomi-noach]

Somewhat repeating @frouioui , will merge once @deepthi 's concern is addressed (likely you need o change ...SQL... to ...Sql... and will then merge.

[timvaillancourt]

Somewhat repeating @frouioui , will merge once @deepthi 's concern is addressed (likely you need o change ...SQL... to ...Sql... and will then merge.

@shlomi-noach the potential issue of s_q_l that Deepthi pointed out didn't seem to be a problem in practice, here is the metric output:

tvaillancourt@REDACTED:~$ curl -s localhost:15000/metrics 2>&1 | grep vttablet_query_sql_text_counts
# HELP vttablet_query_sql_text_counts query sql text counts
# TYPE vttablet_query_sql_text_counts counter
vttablet_query_sql_text_counts{plan="Select",table="Join",workload=""} 3234
vttablet_query_sql_text_counts{plan="Select",table="dual",workload=""} 3650

Let me know if any change is needed. I'll add a changelog/ note once we agree on the metric name and I think we're done! 🙇

[deepthi]

OK, now I understand the intent of this metric, it won't work as implemented. Counters should only be used for monotonically increasing numbers, prometheus will not let you reduce the value of a "counter".
The right type of metric to use here is a Gauge, which can take any value, and change up or down. If I had read the linked issue properly, I would have realized this during the original review.
The name of the metric is also misleading, because it is not a "count" of some specific kind of sql text, it is instead the length in text of the query that is being processed, so the name needs to reflect that.

[deepthi]

QueryTextProcessed will in fact be a better name for the metric.

[deepthi]

@shlomi-noach please feel free to dismiss my review if @timvaillancourt is able complete the requested changes before code freeze.

[timvaillancourt]

OK, now I understand the intent of this metric, it won't work as implemented. Counters should only be used for monotonically increasing numbers, prometheus will not let you reduce the value of a "counter".

@deepthi the intent of this metric is a counter that increments forever so we can infer the rate of query text processed at any given time. I don't believe there is a need to ever reduce this metric, it only increases from the time the daemon starts like other counters

EDIT: here we can see the counter is only incremented by 0 or more: vtg.sqlTextCounts.Add(statsKey, int64(len(sql)))

[deepthi]

OK, now I understand the intent of this metric, it won't work as implemented. Counters should only be used for monotonically increasing numbers, prometheus will not let you reduce the value of a "counter".

@deepthi the intent of this metric is a counter that increments forever so we can infer the rate of query text processed at any given time. I don't believe there is a need to ever reduce this metric, it only increases from the time the daemon starts like other counters

EDIT: here we can see the counter is only incremented by 0 or more: vtg.sqlTextCounts.Add(statsKey, int64(len(sql)))

I think the term count is misleading in this context. Count is typically how many of an entity we encountered, so for example total number of queries. Here we are adding the length of the query each time. A counter will work for this, but I do request that the name be changed to avoid this kind of confusion.

[shlomi-noach]

@timvaillancourt to summarize the current state: the changes make sense, and the metric looks correct. But if you could please rename it to something such as QueryProcessedTextLengths? And with that we can merge the PR.

[timvaillancourt]

But if you could please rename it to something such as QueryProcessedTextLengths

@shlomi-noach / @deepthi I felt Lengths is a bit awkward so I've gone with QueryTextCharactersProcessed which I think is long but very clear. I've also added this to the 20.0.0 changelog

Rerequested your review 🙇

[deepthi]

Some minor wording changes to release notes are required to avoid user confusion. Rest LGTM. @shlomi-noach you may dismiss my review once these changes are done.

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