fix(metrics): label lock wait session pids

Author: Maya P

config/pgwatch-prometheus/metrics.yml

@@ -996,7 +996,7 @@ metrics:
           order by pid, locktype
         )
         select
-          blocked.pid as blocked_pid,
+          blocked.pid::text as tag_blocked_pid,
           current_database() as tag_datname,
           blocked_stm.usename::text as tag_blocked_user,
           blocked_stm.application_name::text as tag_blocked_appname,
@@ -1005,7 +1005,7 @@ metrics:
           coalesce(blocked.relation::regclass::text, blocked_tbl.table_name, '') as tag_blocked_table,
           blocked_stm.query_id::text as tag_blocked_query_id,
           (extract(epoch from (clock_timestamp() - blocked_stm.state_change)) * 1000)::bigint as blocked_ms,
-          blocker.pid as blocker_pid,
+          blocker.pid::text as tag_blocker_pid,
           blocker_stm.usename::text as tag_blocker_user,
           blocker_stm.application_name::text as tag_blocker_appname,
           blocker.mode as blocker_mode,

tests/compliance_vectors/test_work_item_199_lock_waits.py

@@ -0,0 +1,25 @@
+"""Regression coverage for work item 199 lock_waits metric labels."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+
+PROJECT_ROOT = Path(__file__).resolve().parents[2]
+METRICS_FILE = PROJECT_ROOT / "config" / "pgwatch-prometheus" / "metrics.yml"
+
+
+def test_lock_waits_session_pids_are_labels_not_metric_values() -> None:
+    metrics = METRICS_FILE.read_text()
+    lock_waits_sql = metrics.split("  lock_waits:", 1)[1].split("  xmin_horizon:", 1)[0]
+
+    assert "blocked.pid::text as tag_blocked_pid" in lock_waits_sql
+    assert "blocker.pid::text as tag_blocker_pid" in lock_waits_sql
+    assert "blocked.pid as blocked_pid" not in lock_waits_sql
+    assert "blocker.pid as blocker_pid" not in lock_waits_sql
+
+    gauges = lock_waits_sql.split("    gauges:", 1)[1].split("    statement_timeout_seconds:", 1)[0]
+    assert "blocked_pid" not in gauges
+    assert "blocker_pid" not in gauges
+    assert "blocked_ms" in gauges
+    assert "blocker_tx_ms" in gauges