Ver los principales wait events

Oracle

SELECT event, total_waits, time_waited, ROUND(time_waited/100,2) AS sec_waited
FROM v$system_event
WHERE wait_class <> 'Idle'
ORDER BY time_waited DESC
FETCH FIRST 20 ROWS ONLY;
-- For real-time analysis: v$active_session_history (ASH)

v$system_event da los wait events acumulados; v$active_session_history da el muestreo de sesiones activas de los últimos minutos (requiere la licencia Diagnostics Pack).

PostgreSQL

SELECT wait_event_type, wait_event, count(*)
FROM pg_stat_activity
WHERE wait_event IS NOT NULL AND state = 'active'
GROUP BY 1, 2
ORDER BY 3 DESC;

pg_stat_activity muestra el estado de espera actual; muestrearlo repetidamente (polling) revela los wait events más frecuentes.

MySQL

SELECT event_name, count_star, sum_timer_wait,
       ROUND(sum_timer_wait/1000000000000, 2) AS sec_waited
FROM performance_schema.events_waits_summary_global_by_event_name
WHERE count_star > 0
ORDER BY sum_timer_wait DESC
LIMIT 20;

events_waits_summary_global_by_event_name da los tiempos de espera totales por evento (en picosegundos); los instrumentos de espera deben estar habilitados.

SQL Server

SELECT wait_type, waiting_tasks_count, wait_time_ms,
       signal_wait_time_ms, wait_time_ms - signal_wait_time_ms AS resource_wait_ms
FROM sys.dm_os_wait_stats
WHERE wait_time_ms > 0
ORDER BY wait_time_ms DESC;

sys.dm_os_wait_stats muestra los tipos de espera acumulados desde el arranque de la instancia; se puede reiniciar con DBCC SQLPERF.

MongoDB

db.serverStatus().wiredTiger.concurrentTransactions
// For general waits/congestion:
// db.serverStatus().globalLock  and  db.serverStatus().wiredTiger.cache

WiredTiger no tiene wait events clásicos; el agotamiento de concurrentTransactions (tickets), globalLock.currentQueue y la presión de caché indican congestión.

Redis

CONFIG SET latency-monitor-threshold 100
LATENCY LATEST
LATENCY HISTORY command
# For the slowest commands: SLOWLOG GET 10

Una vez configurado el umbral del latency monitor, LATENCY LATEST/HISTORY informa de los eventos que causan más latencia.

Elasticsearch

GET _nodes/hot_threads

_nodes/hot_threads revela cuellos de botella mostrando los stack traces de los hilos que más CPU consumen.