SQL Server Monitoring

Use this skill to check SQL Server health, investigate blocking or deadlocks, monitor SQL Agent jobs, and review the error log.

1. SQL Agent Jobs

Check Job Status

-- All jobs and their last run result
SELECT
    j.name                          AS job_name,
    j.enabled,
    CASE jh.run_status
        WHEN 0 THEN 'Failed'
        WHEN 1 THEN 'Succeeded'
        WHEN 2 THEN 'Retry'
        WHEN 3 THEN 'Cancelled'
        WHEN 4 THEN 'In Progress'
    END                             AS last_run_status,
    msdb.dbo.agent_datetime(jh.run_date, jh.run_time) AS last_run_time,
    -- Duration in HH:MM:SS
    RIGHT('0' + CAST(jh.run_duration / 10000 AS VARCHAR), 2) + ':' +
    RIGHT('0' + CAST((jh.run_duration % 10000) / 100 AS VARCHAR), 2) + ':' +
    RIGHT('0' + CAST(jh.run_duration % 100 AS VARCHAR), 2) AS duration_hhmmss,
    jh.message
FROM msdb.dbo.sysjobs j
LEFT JOIN msdb.dbo.sysjobhistory jh ON j.job_id = jh.job_id
    AND jh.instance_id = (
        SELECT MAX(instance_id) FROM msdb.dbo.sysjobhistory
        WHERE job_id = j.job_id AND step_id = 0
    )
ORDER BY last_run_time DESC;

Find Failed Jobs in Last 24 Hours

SELECT
    j.name                          AS job_name,
    msdb.dbo.agent_datetime(jh.run_date, jh.run_time) AS run_time,
    jh.step_id, jh.step_name,
    jh.message
FROM msdb.dbo.sysjobs j
JOIN msdb.dbo.sysjobhistory jh ON j.job_id = jh.job_id
WHERE jh.run_status = 0   -- 0 = Failed
  AND msdb.dbo.agent_datetime(jh.run_date, jh.run_time) >= DATEADD(HOUR, -24, GETDATE())
ORDER BY run_time DESC;

Currently Running Jobs

SELECT
    j.name          AS job_name,
    ja.start_execution_date,
    DATEDIFF(MINUTE, ja.start_execution_date, GETDATE()) AS running_minutes,
    ja.last_executed_step_id,
    ja.last_executed_step_date
FROM msdb.dbo.sysjobactivity ja
JOIN msdb.dbo.sysjobs j ON ja.job_id = j.job_id
WHERE ja.session_id = (SELECT MAX(session_id) FROM msdb.dbo.syssessions)
  AND ja.start_execution_date IS NOT NULL
  AND ja.stop_execution_date IS NULL;

2. Error Log

-- Read current SQL Server error log
-- Parameters: (log file #, log type, search str1, search str2, start, end, sort order)
EXEC xp_readerrorlog 0, 1, NULL, NULL, NULL, NULL, 'DESC';

-- Filter to errors only (severity 17+)
EXEC xp_readerrorlog 0, 1, 'Error', NULL, NULL, NULL, 'DESC';

-- Check for specific timeframe
DECLARE @start DATETIME = DATEADD(HOUR, -4, GETDATE());
DECLARE @end   DATETIME = GETDATE();
EXEC xp_readerrorlog 0, 1, NULL, NULL, @start, @end, 'DESC';

-- Check previous log file (log rotates on restart)
EXEC xp_readerrorlog 1, 1, NULL, NULL, NULL, NULL, 'DESC';

-- How many error log files exist
EXEC xp_enumerrorlogs;

3. Database Health

-- Status and log reuse reason for all databases
SELECT
    name,
    state_desc,             -- Should be ONLINE; SUSPECT/EMERGENCY = problem
    recovery_model_desc,
    log_reuse_wait_desc,    -- Why log space can't be reused (see below)
    is_read_only,
    is_auto_close_on,       -- Should be OFF in production
    is_auto_shrink_on,      -- Should be OFF in production
    compatibility_level     -- SQL Server version compatibility
FROM sys.databases
ORDER BY name;

logreusewait_desc values:

4. Disk Space

-- Data and log file sizes and free space
SELECT
    DB_NAME(mf.database_id)                             AS database_name,
    mf.name                                             AS logical_name,
    mf.physical_name,
    mf.type_desc,
    mf.size * 8 / 1024                                  AS allocated_mb,
    (mf.size * 8 / 1024) -
        (FILEPROPERTY(mf.name, 'SpaceUsed') * 8 / 1024) AS free_mb,
    FILEPROPERTY(mf.name, 'SpaceUsed') * 8 / 1024      AS used_mb,
    CASE mf.is_percent_growth
        WHEN 1 THEN CAST(mf.growth AS VARCHAR) + '%'
        ELSE CAST(mf.growth * 8 / 1024 AS VARCHAR) + ' MB'
    END                                                 AS auto_growth
FROM sys.master_files mf
ORDER BY database_name, mf.type_desc;

5. Blocking Analysis

Script: ../scripts/blocking-analysis.sql

Quick Blocking Check

-- Sessions that are blocked and what's blocking them
SELECT
    r.session_id,
    r.blocking_session_id,
    r.wait_type,
    r.wait_time / 1000.0        AS wait_time_s,
    r.total_elapsed_time / 1000.0 AS elapsed_s,
    SUBSTRING(t.text, (r.statement_start_offset/2)+1,
        ((CASE r.statement_end_offset WHEN -1 THEN DATALENGTH(t.text)
          ELSE r.statement_end_offset END - r.statement_start_offset)/2)+1) AS blocked_query,
    s.login_name,
    s.host_name
FROM sys.dm_exec_requests r
JOIN sys.dm_exec_sessions s ON r.session_id = s.session_id
CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) t
WHERE r.blocking_session_id > 0
ORDER BY r.wait_time DESC;

Find the Head Blocker

-- The session blocking all others (head of the chain)
SELECT
    s.session_id,
    s.login_name,
    s.host_name,
    s.program_name,
    s.status,
    t.text AS current_or_last_query
FROM sys.dm_exec_sessions s
LEFT JOIN sys.dm_exec_requests r  ON s.session_id = r.session_id
OUTER APPLY sys.dm_exec_sql_text(COALESCE(r.sql_handle, s.sql_handle)) t
WHERE s.session_id IN (
    -- Sessions that ARE blocking someone but are NOT themselves blocked
    SELECT DISTINCT blocking_session_id
    FROM sys.dm_exec_requests
    WHERE blocking_session_id > 0
)
AND s.session_id NOT IN (
    SELECT session_id FROM sys.dm_exec_requests WHERE blocking_session_id > 0
);

⚠️ Using KILL:

-- KILL should only be used after business confirmation that the blocking transaction
-- can be safely terminated. Killing a session rolls back all open transactions.
-- Never execute KILL autonomously.
-- KILL 57;  -- Replace 57 with actual session_id

6. Deadlock Detection

Read from System Health Session

SQL Server captures deadlock graphs automatically in the system_health extended events session.

-- Read deadlock events from system_health ring buffer
SELECT
    xdr.value('@timestamp', 'DATETIME2')       AS deadlock_time,
    xdr.query('.')                              AS deadlock_graph_xml
FROM (
    SELECT CAST(target_data AS XML) AS target_data
    FROM sys.dm_xe_session_targets t
    JOIN sys.dm_xe_sessions s ON t.event_session_address = s.address
    WHERE s.name = 'system_health'
      AND t.target_name = 'ring_buffer'
) AS data
CROSS APPLY target_data.nodes('//RingBufferTarget/event[@name="xml_deadlock_report"]') AS xdt(xdr)
ORDER BY deadlock_time DESC;

Click the deadlockgraphxml result in SSMS to view the graphical deadlock graph.

Read Deadlock Graph

In the deadlock graph:

• Ovals = transactions/processes
• Rectangles = resources (locks)
• Arrows = "this process owns this lock" and "this process is waiting for this lock"
• The process marked with the X was chosen as the deadlock victim (killed by SQL Server)

Common deadlock patterns:

1. Update order deadlock — Two sessions update the same two tables in different order. Fix: standardize update order.
2. Reader-writer deadlock — Reader holds shared lock, writer needs exclusive. Fix: add indexes to reduce scan time; use RCSI.
3. Foreign key deadlock — Parent-child insert/delete in different order. Fix: index foreign key columns on child table.

7. Long-Running Transactions

-- Transactions open longer than 5 minutes
SELECT
    s.session_id,
    s.login_name,
    s.host_name,
    at.transaction_begin_time,
    DATEDIFF(MINUTE, at.transaction_begin_time, GETDATE()) AS open_minutes,
    at.transaction_type,
    at.transaction_state,
    t.text AS last_query
FROM sys.dm_tran_active_transactions at
JOIN sys.dm_tran_session_transactions st ON at.transaction_id = st.transaction_id
JOIN sys.dm_exec_sessions s ON st.session_id = s.session_id
LEFT JOIN sys.dm_exec_requests r ON s.session_id = r.session_id
OUTER APPLY sys.dm_exec_sql_text(COALESCE(r.sql_handle, s.sql_handle)) t
WHERE DATEDIFF(MINUTE, at.transaction_begin_time, GETDATE()) > 5
ORDER BY open_minutes DESC;

Long-running transactions cause:

• Log space not being reused (logreusewaitdesc = ACTIVETRANSACTION)
• Version store bloat in TempDB (if RCSI is enabled)
• Blocking other sessions

Fix: investigate whether the transaction is in an application that forgot to commit, or whether a stored procedure is running longer than expected.