El registro de transacciones crece debido a transacciones de larga duración cuando se usa la captura de datos modificados: SQL Server y Azure SQL
Este artículo le ayuda a supervisar e identificar el problema del crecimiento continuo del registro de transacciones causado por transacciones de larga duración en una base de datos con captura de datos modificados (CDC) habilitada en SQL Server, Azure SQL Database y Azure SQL Instancia administrada.
Síntomas
Considere el caso siguiente:
- Habilite la captura de datos modificados en una base de datos.
- El origen de los datos modificados para CDC es el registro de transacciones. A medida que se aplican las inserciones, actualizaciones y eliminaciones a las tablas de origen sometidas a seguimiento, se agregan al registro las entradas que describen esos cambios.
- El registro de transacciones de la base de datos crece debido a transacciones de larga duración.
- Al consultar sys.databases para la base de datos determinada, la
log_reuse_wait_desccolumna muestraREPLICATION.
En este escenario, el archivo de registro de transacciones de base de datos crece gradualmente, lo que conduce a un consumo excesivo de espacio en el registro de transacciones. Una vez que el tamaño del registro de transacciones alcanza el límite máximo definido, se producirá un error en las escrituras en la base de datos.
Causa
En una base de datos habilitada para CDC, la latencia del trabajo de captura mantiene el truncamiento del registro para asegurarse de que los cambios se pueden capturar del registro de transacciones a las tablas de cambios CDC, lo que impide la pérdida de datos modificados.
Solución alternativa
Puede usar Transact-SQL (T-SQL) para especificar el umbral del registro de transacciones y el intervalo de tiempo para supervisar el registro de transacciones. Si es necesario, puede finalizar las transacciones estableciendo @kill_oldest_tran = 1.
Para supervisar el registro de transacciones, use la siguiente consulta de T-SQL:
DECLARE
-- Log Transactions that generated Txlog over this size
@transaction_log_bytes_used INT = 5242880, -- 5MB (UPDATE)
-- Log full threshold
@log_full_threshold INT = 30, -- Percent (UPDATE)
-- Kill Oldest Tran (0 = FALSE or 1 = TRUE)
@kill_oldest_tran BIT = 0, --(UPDATE)
-- Log Transactions over this duration
@active_tran_time_minutes INT = 15, --(UPDATE)
-- This variable specifies the loop delay, format is Hours:minutes:seconds
@delay VARCHAR(9) = '00:10:00',
@runtime DATETIME,
@starttime DATETIME,
@msg NVARCHAR(100),
@oldest_tran_id BIGINT,
@oldest_tran_session_id INT,
@oldest_tran_begin_time DATETIME,
@killstr NVARCHAR(100)
IF OBJECT_ID('tblDiagLongTransactions') IS NULL
BEGIN
CREATE TABLE tblDiagLongTransactions
(
[datacollectiontime] [datetime] NOT NULL,
[transaction_id] [bigint] NOT NULL,
[name] [nvarchar](32) NOT NULL,
[transaction_begin_time] [datetime] NOT NULL,
[transaction_type] [int] NOT NULL,
[transaction_state] [int] NOT NULL,
[session_id] [int] NOT NULL,
[is_user_transaction] [bit] NOT NULL,
[database_transaction_log_bytes_used] [bigint] NOT NULL,
[login_time] [datetime] NOT NULL,
[last_request_start_time] [datetime] NOT NULL,
[last_request_end_time] [datetime] NULL,
[transaction_isolation_level] [smallint] NOT NULL,
[host_name] [nvarchar](128) NULL,
[nt_user_name] [nvarchar](128) NULL,
[command] [nvarchar](32) NULL,
[status] [nvarchar](30) NULL,
[cpu_time] [int] NULL,
[total_elapsed_time] [int] NULL,
[Transaction_time_in_mins] [int] NULL,
[logical_reads] [bigint] NULL,
[wait_time] [int] NULL,
[wait_type] [nvarchar](60) NULL,
[wait_resource] [nvarchar](256) NULL,
[blocking_session_id] [smallint] NULL,
[program_name] [nvarchar](128) NULL,
[granted_query_memory] [int] NULL,
[writes] [bigint] NULL,
[Request Reads] [bigint] NULL,
[Session Reads] [bigint] NOT NULL,
[Session Logical Reads] [bigint] NOT NULL,
[statement_text] [nvarchar](max) NULL,
[batch_text] [nvarchar](max) NULL,
[objectid] [int] NULL,
[query_hash] BINARY(8),
[query_plan_hash] BINARY(8),
[mostrecentsqltext] [nvarchar](max) NULL
) ON [PRIMARY]
END
WHILE (1=1)
BEGIN
-- Check if the database log used space is over the threshold
SET @runtime = GETDATE()
INSERT INTO tblDiagLongTransactions
SELECT DISTINCT
@runtime AS datacollectiontime,
atr.transaction_id,
atr.name,
transaction_begin_time,
transaction_type,
transaction_state,
dsr.session_id,
dsr.is_user_transaction,
dtr.database_transaction_log_bytes_used,
s.login_time,
s.last_request_start_time,
s.last_request_end_time,
s.transaction_isolation_level,
s.host_name,
s.nt_user_name,
r.command,
r.status,
r.cpu_time,
r.total_elapsed_time,
DATEDIFF(mi, transaction_begin_time, getdate()) AS 'Transaction_time_in_mins',
r.logical_reads,
r.wait_time,
r.wait_type,
r.wait_resource,
r.blocking_session_id,
s.program_name,
r.granted_query_memory,
r.writes,
r.reads AS [Request Reads],
s.reads AS [Session Reads],
s.logical_reads AS [Session Logical Reads],
(REPLACE(REPLACE(REPLACE(REPLACE(SUBSTRING(qt.text, r.statement_start_offset / 2 + 1,
(CASE WHEN r.statement_end_offset = -1 THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2
ELSE r.statement_end_offset
END - r.statement_start_offset) / 2), ' ', ''), CHAR(13), ''), CHAR(10), ''), CHAR(9), '')) AS statement_text,
SUBSTRING(REPLACE(REPLACE(REPLACE(REPLACE(qt.text, ' ', ''), CHAR(13), ''), CHAR(10), ''), CHAR(9), ''), 1, 256) AS batch_text,
qt.objectid,
query_hash,
query_plan_hash,
mqt.text
FROM sys.dm_tran_active_transactions atr
INNER JOIN sys.dm_tran_database_transactions dtr ON atr.transaction_id = dtr.transaction_id
INNER JOIN sys.dm_tran_session_transactions dsr ON atr.transaction_id = dsr.transaction_id
LEFT OUTER JOIN sys.dm_exec_sessions s ON dsr.session_id = s.session_id
LEFT OUTER JOIN sys.dm_exec_connections conn ON s.session_id = dsr.session_id
LEFT OUTER JOIN sys.dm_exec_requests r ON r.session_id = s.session_id
OUTER APPLY sys.dm_exec_sql_text(r.sql_handle) AS qt
OUTER APPLY sys.dm_exec_sql_text(conn.most_recent_sql_handle) AS mqt
WHERE s.session_id != @@spid
AND atr.transaction_type != 2
AND (database_transaction_log_bytes_used > @transaction_log_bytes_used
OR datediff(minute, transaction_begin_time, getdate()) > @active_tran_time_minutes)
-- Check Log full threshold
IF @kill_oldest_tran = 1
BEGIN
IF EXISTS (
SELECT 1 FROM sys.dm_db_log_space_usage
WHERE used_log_space_in_percent >= @log_full_threshold
)
BEGIN
SELECT TOP 1
@oldest_tran_id = atr.transaction_id,
@oldest_tran_begin_time = transaction_begin_time,
@oldest_tran_session_id = dsr.session_id
FROM sys.dm_tran_active_transactions atr
LEFT OUTER JOIN sys.dm_tran_database_transactions dtr ON atr.transaction_id = dtr.transaction_id
LEFT OUTER JOIN sys.dm_tran_session_transactions dsr ON atr.transaction_id = dsr.transaction_id
LEFT OUTER JOIN sys.dm_exec_sessions s ON dsr.session_id = s.session_id
WHERE dsr.session_id != @@spid
AND is_user_transaction = 1
ORDER BY transaction_begin_time DESC
SELECT @oldest_tran_id AS TranID, @oldest_tran_begin_time AS TranbeginTime, @oldest_tran_session_id AS SessionID
SET @killstr = 'KILL ' + CAST(@oldest_tran_session_id AS VARCHAR(100))
PRINT @killstr
-- Kill oldest tran
EXEC (@killstr)
-- Checkpoint
CHECKPOINT
END
END
-- Change the polling interval as required
WAITFOR DELAY @delay
END