Imported from jeremylongshore/tons-of-skills-marketplace (plugins/database/database-transaction-monitor/skills/monitoring-database-transactions/SKILL.md). Install upstream with npx skills add jeremylongshore/tons-of-skills-marketplace --skill monitoring-database-transactions. Copyright stays with the author (MIT).

Database Transaction Monitor

Overview

Monitor active database transactions in real time to detect long-running queries, lock contention, uncommitted transactions, and transaction throughput anomalies across PostgreSQL, MySQL, and MongoDB.

Prerequisites

Database credentials with access to system catalogs (pg_stat_activity, information_schema.PROCESSLIST, or MongoDB currentOp)
psql, mysql, or mongosh CLI installed
Permissions to view other sessions' transactions (PostgreSQL: pg_monitor role; MySQL: PROCESS privilege)
Baseline metrics for normal transaction duration and throughput
Alerting infrastructure (email, Slack webhook, or PagerDuty) for notifications

Instructions

Query the active transaction view to establish a baseline. For PostgreSQL: SELECT pid, state, query_start, now() - query_start AS duration, query FROM pg_stat_activity WHERE state != 'idle' ORDER BY duration DESC. For MySQL: SELECT id, user, host, db, command, time, state, info FROM information_schema.PROCESSLIST WHERE command != 'Sleep'.
Identify long-running transactions by filtering for duration exceeding the application's expected transaction time. Set initial thresholds at 30 seconds for OLTP workloads or 5 minutes for batch/reporting workloads.
Detect idle-in-transaction sessions that hold locks without executing queries. For PostgreSQL: SELECT pid, state, query_start, now() - state_change AS idle_duration FROM pg_stat_activity WHERE state = 'idle in transaction' AND now() - state_change > interval '5 minutes'.
Monitor lock contention by querying the lock manager. For PostgreSQL: SELECT blocked_locks.pid AS blocked_pid, blocking_locks.pid AS blocking_pid, blocked_activity.query AS blocked_query FROM pg_catalog.pg_locks blocked_locks JOIN pg_catalog.pg_locks blocking_locks ON blocking_locks.locktype = blocked_locks.locktype. For MySQL: SELECT * FROM information_schema.INNODB_LOCK_WAITS.
Track transaction throughput by sampling pg_stat_database (xact_commit, xact_rollback) or MySQL Com_commit / Com_rollback status variables at regular intervals. Calculate commits/second and rollback ratio.
Create monitoring scripts that run on a cron schedule (every 30-60 seconds) to capture transaction metrics and write to a time-series store or log file.
Configure alerting thresholds: transactions exceeding 60 seconds, idle-in-transaction sessions exceeding 5 minutes, lock wait queues exceeding 10 waiters, and rollback ratio exceeding 5%.
Build a transaction summary dashboard query that shows: active transaction count, average duration, longest running transaction, lock wait count, and commits-per-second over the last hour.
Implement automatic remediation for known-safe scenarios: terminate idle-in-transaction sessions older than 30 minutes using SELECT pg_terminate_backend(pid) (PostgreSQL) or KILL connection_id (MySQL), with logging of terminated sessions.
Generate weekly transaction health reports summarizing peak transaction counts, P95/P99 duration percentiles, deadlock occurrences, and long-running transaction incidents.

Output

Transaction monitoring queries tailored to the specific database engine in use
Monitoring scripts (shell or Python) for scheduled transaction health checks
Alert configuration with threshold definitions and notification channel setup
Dashboard queries showing transaction throughput, duration distribution, and lock metrics
Weekly health report template with transaction performance trends and anomaly highlights

Error Handling

Error	Cause	Solution
`pg_stat_activity` returns no rows for other sessions	Missing `pg_monitor` role or `track_activities` disabled	Grant `pg_monitor` role; set `track_activities = on` in postgresql.conf
Lock monitoring query times out	Massive lock table during contention storm	Query `pg_locks` with a statement_timeout; reduce monitoring frequency during incidents
False positive alerts for long-running transactions	Batch jobs or maintenance operations trigger duration alerts	Create an exclusion list for known batch job PIDs or application users; use separate thresholds for batch vs OLTP
Transaction throughput drops to zero	Connection pool exhaustion or database crash	Check `max_connections` usage; verify database process is running; check for full disk or OOM conditions
Monitoring queries add overhead	High-frequency polling of system catalogs	Reduce polling interval to every 60 seconds; use `pg_stat_statements` for aggregated stats instead of per-query monitoring

Examples

Detecting a connection leak in a web application: Transaction count steadily increases over hours while commit rate remains flat. Monitoring reveals hundreds of idle in transaction sessions from the application server. Root cause: missing connection.close() in error handling paths. Resolution: terminate stale sessions and fix application connection management.

Identifying lock contention during peak hours: Dashboard shows lock wait count spiking from 0 to 50+ between 2-4 PM daily. Lock analysis reveals a nightly reporting query overlapping with high-volume order processing. Resolution: reschedule reporting queries to off-peak hours and add NOWAIT hints to critical transaction paths.

Tracking transaction rollback ratio spike: Rollback ratio jumps from 1% to 15% after a deployment. Transaction monitor logs show serialization failures on a frequently updated inventory table. Resolution: reduce transaction isolation level from SERIALIZABLE to READ COMMITTED for non-critical paths and add retry logic for serialization failures.

Resources

PostgreSQL monitoring views: https://www.postgresql.org/docs/current/monitoring-stats.html
MySQL performance schema: https://dev.mysql.com/doc/refman/8.0/en/performance-schema.html
MongoDB currentOp: https://www.mongodb.com/docs/manual/reference/method/db.currentOp/
pg_stat_statements extension: https://www.postgresql.org/docs/current/pgstatstatements.html
Lock monitoring best practices: https://wiki.postgresql.org/wiki/Lock_Monitoring

monitoring-database-transactions

About