Vtgate metrics: Added plan and query type metrics

[harshit-gangal]

Description

This PR adds classification of query plans based on their execution strategy.
Additionally, this PR introduces a new metrics counter, QueryProcessed, which tracks queries processed at VTGate with labels for Query, Plan, and Tablet type. This metric provides better observability into query distribution and execution patterns

Plan Classification

Query plans are categorized into different types based on their execution behavior:

• Local – Queries executed locally on VTGate without involving any shard.
• Passthrough – Queries forwarded to single shard without having any additional processing at VTGate.
• MultiShard – Queries executed across multiple shards with controlled routing.
• Lookup – Queries using lookup vindexes to resolve keyspace IDs efficiently and route to specific shards.
• Scatter – Queries broadcast to all shards.
• JoinOp – Queries involving join operations across multiple shards, with Join on VTGate.
• ForeignKey – Queries handling foreign key constraints, such as cascades and validations.
• Complex – Queries with intricate execution logic requiring VTGate to process results.
• OnlineDDL – DDLs executed though Online Schema change workflow.
• DirectDDL – DDLs directly executed on the shards.
• Transaction – Queries managing transactions, including BEGIN, COMMIT, ROLLBACK, and SAVEPOINT.
• Topology - Queries that involves accessing Topology Server for Get/Put.

Published Metrics

Sample metrics from VTGate's /metrics path:

# HELP vtgate_query_processed Query processed at vtgate by query, plan, and tablet type
# TYPE vtgate_query_processed counter
vtgate_query_processed{plan="Complex",query="SET",tablet="PRIMARY"} 1
vtgate_query_processed{plan="Local",query="USE",tablet="PRIMARY"} 1
vtgate_query_processed{plan="MultiShard",query="DELETE",tablet="PRIMARY"} 1
vtgate_query_processed{plan="MultiShard",query="UPDATE",tablet="PRIMARY"} 1
vtgate_query_processed{plan="Passthrough",query="SHOW",tablet="PRIMARY"} 1
vtgate_query_processed{plan="Scatter",query="DELETE",tablet="PRIMARY"} 20
vtgate_query_processed{plan="Scatter",query="SELECT",tablet="PRIMARY"} 1
vtgate_query_processed{plan="Transaction",query="ROLLBACK",tablet="PRIMARY"} 1
vtgate_query_processed{plan="Transaction",query="SAVEPOINT",tablet="PRIMARY"} 1

# HELP vtgate_query_routed Query routed from vtgate to vttablet by query, plan, and tablet type
# TYPE vtgate_query_routed counter
vtgate_query_routed{plan="Complex",query="SET",tablet="PRIMARY"} 0
vtgate_query_routed{plan="Local",query="USE",tablet="PRIMARY"} 0
vtgate_query_routed{plan="MultiShard",query="DELETE",tablet="PRIMARY"} 2
vtgate_query_routed{plan="MultiShard",query="UPDATE",tablet="PRIMARY"} 2
vtgate_query_routed{plan="Passthrough",query="SHOW",tablet="PRIMARY"} 1
vtgate_query_routed{plan="Scatter",query="DELETE",tablet="PRIMARY"} 56
vtgate_query_routed{plan="Scatter",query="SELECT",tablet="PRIMARY"} 2
vtgate_query_routed{plan="Transaction",query="ROLLBACK",tablet="PRIMARY"} 0
vtgate_query_routed{plan="Transaction",query="SAVEPOINT",tablet="PRIMARY"} 0

Related Issue(s)

• RFC: New vtgate Metrics #17585

Checklist

• 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 Doc: Query Plans Classification and Monitoring website#1935

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[codecov]

Codecov Report

Attention: Patch coverage is 94.75983% with 12 lines in your changes missing coverage. Please review.

Project coverage is 67.45%. Comparing base (000fbbe) to head (6c55d04).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtgate/engine/plan.go	93.02%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17727      +/-   ##
==========================================
- Coverage   67.95%   67.45%   -0.50%     
==========================================
  Files        1586     1592       +6     
  Lines      255208   258189    +2981     
==========================================
+ Hits       173423   174165     +742     
- Misses      81785    84024    +2239     

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[harshit-gangal]

Website Doc PR: vitessio/website#1935

[deepthi]

I understand that we can't re-use QueriesProcessed and QueriesRouted, because that might break people's dashboards, but we need to come up with some other names for QueryProcessed and QueryRouted which are grammatical. Leaving this comment as a place-holder while I try to think of alternatives.

[deepthi]

I understand that we can't re-use QueriesProcessed and QueriesRouted, because that might break people's dashboards, but we need to come up with some other names for QueryProcessed and QueryRouted which are grammatical. Leaving this comment as a place-holder while I try to think of alternatives.

Here are my suggestions

• QueryProcessed -> QueryCounts
• QueryRouted -> QueryRouteCounts

[harshit-gangal]

• QueryProcessed -> QueryCounts
• QueryRouted -> QueryRouteCounts

Count is self-explanatory, as it already implies a counter. Using Counts looks redundant in this context.

[frouioui]

It could be good to have a link to the docs here as a comment (https://github.com/vitessio/website/pull/1935/files#diff-4badcfb66b7411dea206a299af9b9f8e3d349d817ad332798f747b0b9a40ad9f), both to help us know what each value mean and also to remind us that modifying this list implies that we need to change the docs.

[frouioui]

Looks good to me, just QueryRouted -> "query" in singular feels a bit odd. But I don't have better suggestion for the name. Not approving as deepthi has an ongoing conversation.

[GuptaManan100]

LGTM to me too

[deepthi]

• QueryProcessed -> QueryCounts
• QueryRouted -> QueryRouteCounts

Count is self-explanatory, as it already implies a counter. Using Counts looks redundant in this context.

The problem is that we don't have any good options because QueriesProcessed is taken. I proposed Counts because we already have that on vttablet, so there is precedence for it.
If you don't like that, then the next proposal is simply "Queries" and "QueryRoutes" :)

[deepthi]

We seem to be dropping the table metrics. Can we add that as a dimension to the new metrics? They have been useful in the past in debugging production issues.

[deepthi]

In code you are deprecating the table metrics, but that is missing from here.

[deepthi]

Suggested change

	1. QueryProcessed - This counts the number of query executed.
	1. QueryProcessed - This counts the number of queries processed by this vtgate.

[deepthi]

This says shards but the actual description of the metric says "routed to vttablets". Which one is it?

[deepthi]

Suggested change

	queryProcessed = stats.NewCountersWithMultiLabels("QueryProcessed", "Query processed at vtgate by query, plan, and tablet type", []string{"Query", "Plan", "Tablet"})
	queryProcessed = stats.NewCountersWithMultiLabels("QueryProcessed", "Count of queries processed by query, plan and tablet type", []string{"Query", "Plan", "Tablet"})

[deepthi]

Suggested change

	queryRouted = stats.NewCountersWithMultiLabels("QueryRouted", "Query routed from vtgate to vttablet by query, plan, and tablet type", []string{"Query", "Plan", "Tablet"})
	queryRouted = stats.NewCountersWithMultiLabels("QueryRouted", "Count of queries routed to vttablets by query, plan and tablet type", []string{"Query", "Plan", "Tablet"})