Fix PostgreSQL Dashboard — PromQL label mismatch

[mac119]

PR: Fix PostgreSQL Dashboard — PromQL label mismatch causing "No Data" panels

Summary

Fix two panels in the PostgreSQL Metrics dashboard that display "No Data" due to PromQL binary operation label mismatch. The postgresql_backends metric carries a postgresql_database_name label, while postgresql_connection_max does not. When PromQL performs arithmetic between two vectors, it requires matching label sets on both sides — mismatched labels result in empty results.

Additionally, the Connection Utilization % panel legend template {postgresql_database_name} renders as a raw string because sum() aggregation removes all labels, making the template variable unresolvable.

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Problem

Root Cause: Label Mismatch in PromQL Binary Operations

The OpenTelemetry PostgreSQL receiver emits metrics with different label sets:

Metric	Labels
postgresql_backends	postgresql_database_name, service_instance_id, instrumentation_library_name, ...
postgresql_connection_max	service_instance_id, instrumentation_library_name, ... (no postgresql_database_name)

When performing division postgresql_backends / postgresql_connection_max, PromQL requires exact label matching between left and right operands. Since postgresql_backends has an extra postgresql_database_name label, no vector elements match → result is empty ("No Data").

Affected Panels

1. Connection Utilization %

• Symptom: Shows "No Data"
• Secondary issue: Legend displays raw template {postgresql_database_name} instead of a meaningful name

2. Database Health Score

• Symptom: Shows "No Data"
• Cause: Same label mismatch issue in the compound formula where postgresql_backends, postgresql_connection_max, postgresql_blks_hit, postgresql_blks_read, postgresql_commits, and postgresql_rollbacks all have different label sets

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Fix

Wrap all metrics in sum() to aggregate away label dimensions before performing arithmetic. This ensures both sides of binary operations have matching (empty) label sets.

Panel: Connection Utilization %

Before:

(postgresql_backends / postgresql_connection_max)

After:

(sum(postgresql_backends) / sum(postgresql_connection_max)) * 100

Legend fix: Changed from {postgresql_database_name} → Utilization %

• Reason: sum() removes all labels, so template variables cannot be resolved and render as raw strings.

Panel: Database Health Score

Before:

((rate(postgresql_blks_hit[5m]) / (rate(postgresql_blks_hit[5m]) + rate(postgresql_blks_read[5m]))) * 0.40)
+ ((rate(postgresql_commits[5m]) / (rate(postgresql_commits[5m]) + rate(postgresql_rollbacks[5m]))) * 0.30)
+ (((postgresql_connection_max - postgresql_backends) / postgresql_connection_max) * 0.30)

After:

((sum(rate(postgresql_blks_hit[5m])) / (sum(rate(postgresql_blks_hit[5m])) + sum(rate(postgresql_blks_read[5m])))) * 0.40)
+ ((sum(rate(postgresql_commits[5m])) / (sum(rate(postgresql_commits[5m])) + sum(rate(postgresql_rollbacks[5m])))) * 0.30)
+ (((sum(postgresql_connection_max) - sum(postgresql_backends)) / sum(postgresql_connection_max)) * 0.30)

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Verification

Tested against OpenObserve with otelcol-contrib v0.151.0 collecting from PostgreSQL 18.3:

# Connection Utilization % — returns 3 (i.e., 3%)
$ curl -s "http://localhost:5080/api/default/prometheus/api/v1/query" \
  --data-urlencode "query=(sum(postgresql_backends) / sum(postgresql_connection_max)) * 100"
{"status":"success","data":{"resultType":"vector","result":[{"metric":{},"value":[1778147712,"3"]}]}}

# Database Health Score — returns ~0.99
$ curl -s "http://localhost:5080/api/default/prometheus/api/v1/query" \
  --data-urlencode "query=((sum(rate(postgresql_blks_hit[5m])) / ...) * 0.40) + ..."
{"status":"success","data":{"resultType":"vector","result":[{"metric":{},"value":[1778147729,"0.991"]}]}}

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Environment

• OpenObserve: latest (running on localhost:5080)
• otelcol-contrib: v0.151.0
• PostgreSQL: 18.3
• OS: Ubuntu 22.04 (Linux x86_64)

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Files Changed

• PostgreSQL Metrics/PostgreSQL.dashboard.json
  • Fixed Connection Utilization % panel query and legend
  • Fixed Database Health Score panel query

[mac119]

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