初衷：簡單來說，開啟該選項，使得單機分發庫在宕機時，利用最近的系統數據庫和用戶數據庫備份，還原到一臺新的服務器上，即可使復制繼續工作成為可能。
需要注意的是：在分發庫開啟該選項，意味著發布庫的日志只有在分發庫被備份后才會截斷。
查看該選項是否開啟：
SELECT name,is_sync_with_backup FROM sys.databases WHERE name LIKE 'distribution%'
開啟該選項：
sp_replicationdboption 'distribution','sync with backup','true'
場景：
在生產環境中，分發庫備份為半小時一次。
將主體從ServerA切換至ServerB時，Logreader Agent報錯：
直觀上可以看到，Logreader 認為dist_backup_lsn和dist_last_sn不一致，導致其無法繼續工作。下面我們實際去看一下這兩者到底是否一致。
下面是Logreader、Distribution Agent工作的步驟列表，為了方便，我都貼出來：
Log Reader Agent (logread.exe) – Sequence of Steps1.Calls sp_MSadd_LogReader_History to write to MSLogReader_History – “Starting Agent”2.sp_MShelp_logreader_agentid – Obtain log reader agent specific information for that publication 3.sp_MShelp_PRofile – Obtains profile information for the Log Reader4.MSadd_logreader_history to write MSlogreader_history – “Initializing” 5.sp_MSget_last_transaction – determine where the log reader agent left off reading the log. 6.Read the transaction log – sp_replcmds 7.Processes the returned commands from the sp_replcmds in batches by calling sp_MSadd_repl_commands 8.Marks this transaction as committed in distribution database by using sp_repldone procedure 9.Adjusts the identity range if necessary and if you are using Automatic Identity Range Management y calling sp_MSpub_adjust_identity 10.Calls sp_MSget_last_transaction to check the last transaction read and stored in MSReplication_transactions table 11.When all transactions are read, LogRead.exe calls sp_MSAdd_logreader_history and writes message to MSLogReader_history “1 transactions with 9 commands were delivered”•Distribution Agent (distrib.exe) - Sequence of Steps1.master.db.sp_msget_jobstate – get the status of the job (if it is already started) 2.sp_Msadd_distribution_history – MSDistribution_history – Starting agent 3.sp_MSSubscription_Status – whether subscription has expired or the snapshot is ready 4.sp_server_info- determines the collation 5.sp_mshelp_subscriber_info – retrieve subscriber information 6.sp_mshelp_subscription_agentid – determine the name of the distribution agent 7.sp_Msadd_distribution_history – Initializing message – Msrepl_distribution_history 8.sp_Msadd_distribution_history – Connecting to Subscriber - Msrepl_distribution_history 9.so_datatype_info – to determine the data type mapping necessary to create the tracking table necessary for the Distribution agent 10.sp_MScheck_subscribe on subscription database – verifies that SQL Server Agent account is in sysadmin and db_owner role in subscription database 11.sp_mscreate_sub_tables on subscriber in subscription database – creates MSSusbcription_agents and MSreplication_subscriptions tables 12.Sp_MSinit_Subscription_agent – updates the Subscription agent information on subscription database 13.Retrieves transaction_timestamp and subscription_guid to determine what Distribution agent has already replicated to the Subscriber. Transaction_timestamp correlates to xact_seqno column in MSReplication_transactions table in distribution database. All values large than the xact_seqno will be replicated 14.If we are doing initial sync, Distribution Agent calls sp_MSupdatelastsyncinfo which updates MSreplication_susbcriptions and MSSusbcription_agents table 15.Starts to retrieve all transactions and their corresponding commands from MSReplication_transactions and MSreplication_commands table where transaction_timestamp column in subscription database < xact_seqno column in MSreplication_transactions table. Applies the transaction using sp_MS_get_repl_commands procedure 16.Issues dynamic SQL to update the MSreplication_subscriptions table with the last delivered transaction ID 17.sp_MSDistribution_history to write the MSrepl_distribution_history table with status message “nn transaction(S) with nn command(s) were delivered”
在步驟5中，我們得知，Logreader用存儲過程sp_Msget_last_transaction來定位發布庫日志中最后一個被寫入到分發庫中的事務，我們找到這個存儲過程的源碼：
CREATE PROCEDURE sys.sp_MSget_last_transaction( @publisher_id int = NULL, @publisher_db sysname, @publisher sysname = NULL, @max_xact_seqno varbinary(16) = NULL output ,@for_truncate bit = 0)ASbegin declare @publisher_database_id int declare @max_xact_id varbinary(16) declare @sync_bit int declare @sync_with_backup bit set nocount on -- security check -- only db_owner can execute this if (is_member ('db_owner') != 1) begin raiserror(14260, 16, -1) return (1) end SELECT @sync_bit = 32 if @publisher_id is NULL select @publisher_id = srvid from master.dbo.sysservers where UPPER(srvname) = UPPER(@publisher) -- Get publisher database id. SELECT @publisher_database_id = id from MSpublisher_databases where publisher_id = @publisher_id and publisher_db = @publisher_db if exists ( select * from master.dbo.sysdatabases where name = db_name() and category & @sync_bit = 0) select @sync_with_backup = 0 else select @sync_with_backup = 1 if @for_truncate = 0 begin select top 1 @max_xact_id = rt.xact_id, @max_xact_seqno = rt.xact_seqno from MSrepl_transactions rt where rt.publisher_database_id = @publisher_database_id and not xact_id = 0x0 order by xact_seqno desc end -- If (1) requesting truncate lsn (distbackuplsn), (2) sync with backup is set -- query the values from MSrepl_backup_lsn else if @sync_with_backup = 1 begin -- Get the last backed up lsn if available. select top 1 @max_xact_id = valid_xact_id, @max_xact_seqno = valid_xact_seqno from MSrepl_backup_lsns where publisher_database_id = @publisher_database_id end -- If @publisher is not null, we are calling this sp from sp_replrestart -- Don't return result set. if @publisher is null select @max_xact_id, @max_xact_seqno, @publisher_database_id -- Don't return any result when requsting a truncate lsn and -- the database is not in 'sync with backup' mode, which signal the -- distribution agent to use last dist lsn to call sp_repldone. where not (@sync_with_backup = 0 and @for_truncate = 1)end 存儲過程中，代碼
else if @sync_with_backup = 1begin -- Get the last backed up lsn if available. select top 1 @max_xact_id = valid_xact_id, @max_xact_seqno = valid_xact_seqno from MSrepl_backup_lsns where publisher_database_id = @publisher_database_idend
可見，報錯中的dist_backup_lsn取自表MSrepl_backup_lsns
我們來查詢一下該表：
select * from MSrepl_backup_lsns
列valid_xact_id為最后備份的事務ID，valid_xact_seqno為該事務中的LSN，即valid_xact_seqno為報錯中顯示的dist_backup_lsn，（請勿與圖中貼出的錯誤進行對比，上圖僅為錯誤示例截圖）。
我們再去分發庫MSrepl_transactions表中找到當前已經被讀取到分發庫的最大事務的LSN
SELECT TOP 1 * from [dbo].[MSrepl_transactions] as twhere t.publisher_database_id = 5ORDER BY t.entry_time DESC
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