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Add `QueryAnalyzers::GitlabSchemasMetrics` as a way to observe used schemas

Kamil Trzciński (Back 2025-01-01) requested to merge monitor-query-schemas into master

What does this MR do and why?

This is based on top of !73827 (merged), which needs to be merged first.

This is based on top of !74076 (merged), which needs to be merged first.

This analyzers output is Prometheus metrics observing connections vs gitlab schemas of executed queries.

It will present well in a single metric how many connections do cross-join or are misplaced once additional databases are configured.

This will observe all queries executed and increment prometheus counter gitlab_database_decomposition_gitlab_schemas_used.

This effectively allows to see in a single metric depending on a Phase:

  1. In Phase 1/2: since we have only single main/main_replica: a number of queries that are either gitlab_main, gitlab_ci, gitlab_ci/gitlab_main
  2. In Phase 3: since we have main/main_replica/ci_replica: a number of misaligned queries that if go to ci_replica: are not only gitlab_ci, but gitlab_main / gitlab_ci,gitlab_main
  3. In Phase 4: since we have main/main_replica/ci/ci_replica: a number of misaligned queries that that cross boundaries main: accessing gitlab_ci schema, etc.

Related to:

Results

Today it produces results similar to this since not all DB models are yet described, they will be !73839 (merged):

gitlab_database_decomposition_gitlab_schemas_used{db_config_name="ci",gitlab_schemas="undefined_pg_attrdef,undefined_pg_attribute,undefined_pg_collation,undefined_pg_type"} 0
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="ci",gitlab_schemas="undefined_pg_class,undefined_pg_namespace"} 0
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main",gitlab_schemas="gitlab_main"} 0
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main",gitlab_schemas="gitlab_shared"} 0
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main",gitlab_schemas="undefined_pg_attrdef,undefined_pg_attribute,undefined_pg_collation,undefined_pg_type"} 4
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main",gitlab_schemas="undefined_pg_attribute,undefined_pg_index"} 4
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main",gitlab_schemas="undefined_pg_class,undefined_pg_namespace"} 2
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main_replica",gitlab_schemas="gitlab_main"} 22
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="main_replica",gitlab_schemas="gitlab_shared"} 2
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="unknown",gitlab_schemas="undefined_pg_range,undefined_pg_type"} 0
gitlab_database_decomposition_gitlab_schemas_used{db_config_name="unknown",gitlab_schemas="undefined_pg_type"} 40

How to set up and validate locally

  1. Enable the query analyzer 
    Feature.enable(:query_analyzer_gitlab_schema_metrics)
  2. Visit any group or project member pages such as http://127.0.0.1:3000/groups/flightjs/-/group_members
  3. Go to http://127.0.0.1:3000/-/metrics and look for gitlab_database_decomposition_gitlab_schemas_used

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

Edited by Kamil Trzciński (Back 2025-01-01)

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