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

[vitess-bot]

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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 67.96%. Comparing base (000fbbe) to head (aa4c4c7).
Report is 2 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%   67.96%            
========================================
  Files        1586     1586            
  Lines      255208   255373   +165     
========================================
+ Hits       173423   173560   +137     
- Misses      81785    81813    +28     

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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.