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SQL Server Always On延迟观测和预警

本文主要是介绍SQL Server Always On延迟观测和预警,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!

延迟是AlwaysON的最大敌人之一。对AlwaysON而言,其首要目标就尽量减少(无法避免)主副本、辅助副本的数据延迟,实现主副本、辅助副本的“数据同步”。只有主副本、辅助副本的同步延迟越小越高,只读访问的实性性才会越高,数据库的RTO(Estimating Failover Time )和RPO(Estimating Potential Data Loss)也才会越小。

但延迟可能存在于AlwaysON同步的各个环节中,因此,在分析现延迟情况时,应该首先理解AlwaysON的同步过程,然后切分到每个过程中进行监控和分析。

 

AlwaysON同步的6大步骤

在我的上篇文章《AlwaysON的同步原理及同步模式》中,曾介绍过AlwaysON的同步过程。归结起来,主要包括如下六个步骤:

① log flush(primary)

② log capture(primary)

③ send(primary and secondary)

④ log receive and cache(secondary)

⑤ log hardened(secondary)

⑥ redo(secondary)

前两个步骤发生在主副本,最后三个步骤发生在辅助副本,中间的第三个步骤发生主副本和辅助副本之间。

另外,如果是同步提交模式,还需要增加一个步骤:辅助副本在步骤5之后,会发送一个(日志硬化)确认信息给主副本,然后才能进入redo阶段。

 

 

通过扩展事件跟踪,我们可以知道日志块移动的每个步骤,并且可以确切地知道事务延迟来自何处。

 

通常,延迟来自三个部分:

  • 主库日志固化的持续时间:它等于Log_flush_start(步骤2)和Log_flush_complete(步骤3)的时间之和。
  • 从库日志固化的持续时间:它等于Log_flush_start(步骤10)和Log_flush_complete(步骤11)的时间之和。
  • 网络传送的持续时间 :primary:hadr_log_block_send_complete-> secondary:hadr_transport_receive_log_block_message(步骤6-7)和(secondary:hadr_lsn_send_complete-> primary:hadr_receive_harden_lsn_message(步骤12-13)的时间之和

创建扩展事件:

/* Note: this trace could generate very large amount of data very quickly, 
depends on the actual transaction rate. On a busy server it can grow several GB per minute, 
so do not run the script too long to avoid the impact to the production server.  */
 
CREATE EVENT SESSION [AlwaysOn_Data_Movement_Tracing] ON SERVER  
     ADD EVENT sqlserver.file_write_completed, 
     ADD EVENT sqlserver.file_write_enqueued, 
     ADD EVENT sqlserver.hadr_apply_log_block, 
     ADD EVENT sqlserver.hadr_apply_vlfheader, 
     ADD EVENT sqlserver.hadr_capture_compressed_log_cache, 
     ADD EVENT sqlserver.hadr_capture_filestream_wait, 
     ADD EVENT sqlserver.hadr_capture_log_block, 
     ADD EVENT sqlserver.hadr_capture_vlfheader, 
     ADD EVENT sqlserver.hadr_db_commit_mgr_harden, 
     ADD EVENT sqlserver.hadr_db_commit_mgr_harden_still_waiting, 
     ADD EVENT sqlserver.hadr_db_commit_mgr_update_harden, 
     ADD EVENT sqlserver.hadr_filestream_processed_block, 
     ADD EVENT sqlserver.hadr_log_block_compression, 
     ADD EVENT sqlserver.hadr_log_block_decompression, 
     ADD EVENT sqlserver.hadr_log_block_group_commit , 
     ADD EVENT sqlserver.hadr_log_block_send_complete, 
     ADD EVENT sqlserver.hadr_lsn_send_complete, 
     ADD EVENT sqlserver.hadr_receive_harden_lsn_message, 
     ADD EVENT sqlserver.hadr_send_harden_lsn_message, 
     ADD EVENT sqlserver.hadr_transport_flow_control_action, 
     ADD EVENT sqlserver.hadr_transport_receive_log_block_message, 
     ADD EVENT sqlserver.log_block_pushed_to_logpool, 
     ADD EVENT sqlserver.log_flush_complete , 
     ADD EVENT sqlserver.log_flush_start, 
     ADD EVENT sqlserver.recovery_unit_harden_log_timestamps  
     ADD TARGET package0.event_file(SET filename=N'c:\mslog\AlwaysOn_Data_Movement_Tracing.xel',max_file_size=(500),max_rollover_files=(4)) 
WITH (MAX_MEMORY=4096 KB,
      EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,
      MAX_DISPATCH_LATENCY=30 SECONDS,
      MAX_EVENT_SIZE=0 KB,
      MEMORY_PARTITION_MODE=NONE,
      TRACK_CAUSALITY=OFF,
      STARTUP_STATE=ON
) 
GO 

 

Always ON预警

IF EXISTS(SELECT 1 FROM sys.objects o WHERE o.[object_id]=OBJECT_ID('[dbo].[Proc_DBA_AlwaysonWarning]') AND o.[type] IN(N'P',N'PC'))
    DROP PROC [dbo].[Proc_DBA_AlwaysonWarning]
GO
-- =============================================
-- Description:    alwayson预警
-- Remark     : 所有参数均为产生预警的参数
-- =============================================
CREATE PROCEDURE dbo.Proc_DBA_AlwaysonWarning
    @syncMode BIT=NULL,                --"同步模式" 是否为同步提交,是1否0,如为NULL则不处理。默认为 NULL (不处理是否异步)
    @syncStateIsFinished BIT=0,        --"同步状态" 是否为 "SYNCHRONIZED",是1否0,如为NULL则不处理。默认为 0 (如同步状态为未完成则预警)
    @syncHealth BIT=0,                --"同步健康状态" 是否为健康, 是1否0,如为NULL则不处理。默认为 0 否 (如健康状态为不健康则预警)
    @redoDelaySeconds INT=600,        --"Redo延迟(秒)"         > 多少则预警。默认为 600 (s)
    @logDelaySeconds INT=600,        --"Log传送延迟(秒)"      > 多少则预警。默认为 600 (s)
    @redoWaitQueueKB BIGINT=10240,    --"Redo等待队列(KB)"     > 多少则预警。默认为 10240 (10MB)
    @logWaitQueueKB BIGINT=524288    --"Log传送等待队列(KB)"  > 多少则预警。默认为 524288 (512MB)
AS
BEGIN
    SET NOCOUNT ON;
    ;WITH t AS (
        SELECT  
                ar.replica_server_name AS [副本名称] ,
                ar.availability_mode_desc as [同步模式],
                DB_NAME(dbr.database_id) AS [数据库名称] ,
                dbr.database_state_desc AS [数据库状态],
                dbr.synchronization_state_desc AS [同步状态],
                dbr.synchronization_health_desc AS [同步健康状态],
                ISNULL(CASE dbr.redo_rate
                         WHEN 0 THEN -1
                         ELSE CAST(dbr.redo_queue_size AS FLOAT) / dbr.redo_rate
                       END, -1) AS [Redo延迟(秒)] ,
                ISNULL(CASE dbr.log_send_rate
                         WHEN 0 THEN -1
                         ELSE CAST(dbr.log_send_queue_size AS FLOAT)
                              / dbr.log_send_rate
                       END, -1) AS [Log传送延迟(秒)] ,
                dbr.redo_queue_size AS [Redo等待队列(KB)] ,
                dbr.redo_rate AS [Redo速率(KB/S)] ,
                dbr.log_send_queue_size AS [Log传送等待队列(KB)] ,
                dbr.log_send_rate AS [Log传送速率(KB/S)]
        FROM    [master].sys.availability_replicas AS AR
                INNER JOIN [master].sys.dm_hadr_database_replica_states AS dbr 
                ON ar.replica_id = dbr.replica_id
        WHERE   dbr.redo_queue_size IS NOT NULL
    )
    /*
    @syncMode BIT=NULL,                --"同步模式" 是否为同步提交,是1否0,如为NULL则不处理。默认为 NULL (不处理是否异步)
    @syncStateIsFinished BIT=0,        --"同步状态" 是否为 "SYNCHRONIZED",是1否0,如为NULL则不处理。默认为 0 (如同步状态为未完成则预警)
    @syncHealth BIT=0,                --"同步健康状态" 是否为健康, 是1否0,如为NULL则不处理。默认为 0 否 (如健康状态为不健康则预警)
    @redoDelaySeconds INT=60,        --"Redo延迟(秒)"         > 多少则预警。默认为 60  (s)
    @logDelaySeconds INT=600,        --"Log传送延迟(秒)"      > 多少则预警。默认为 600 (s)
    @redoWaitQueueKB BIGINT=10240,    --"Redo等待队列(KB)"     > 多少则预警。默认为 10240 (10MB)
    @logWaitQueueKB BIGINT=524288,    --"Log传送等待队列(KB)"  > 多少则预警。默认为 524288 (512MB)
    */
    SELECT  
        CASE WHEN
            ( (@syncMode=0 AND [同步模式]!='SYNCHRONOUS_COMMIT') or ( @syncMode=1 AND [同步模式]='SYNCHRONOUS_COMMIT' ) )
            OR
            ( (@syncStateIsFinished=0 AND [同步状态]!='SYNCHRONIZED') or ( @syncStateIsFinished=1 AND [同步状态]='SYNCHRONIZED' ) )
            OR
            ( (@syncHealth=0 AND [同步健康状态]!='HEALTHY') or ( @syncHealth=1 AND [同步健康状态]='HEALTHY' ) )
            OR
            ( [Redo延迟(秒)] > @redoDelaySeconds )
            OR
            ( [Log传送延迟(秒)] > @logDelaySeconds )
            OR
            ( [Redo等待队列(KB)] > @redoWaitQueueKB )
            OR
            ( [Log传送等待队列(KB)] > @logWaitQueueKB )
            THEN 1 ELSE 0 END AS Warning,
        [副本名称],
        [同步模式],
        [数据库名称],
        [数据库状态],
        [同步状态],
        [同步健康状态],
        [Redo延迟(秒)],
        [Log传送延迟(秒)],
        [Redo等待队列(KB)],
        [Redo速率(KB/S)],
        [Log传送等待队列(KB)],
        [Log传送速率(KB/S)]
    FROM t
END
GO
EXEC sys.sp_addextendedproperty 
    @name=N'Version', @value=N'2.0' , 
    @level0type=N'SCHEMA',@level0name=N'dbo', 
    @level1type=N'PROCEDURE',@level1name=N'Proc_DBA_AlwaysonWarning'

 

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