Working with Microsoft SQL Server AlwaysOn Availability Groups

The Microsoft SQL Server AlwaysOn Availability Groups feature is a high-availability, disaster-recovery solution that provides an enterprise-level alternative to database mirroring.

Prerequisites

Credentials used for connecting to individual replicas should be identical to those used for connecting to the AlwaysOn Listener.

Replicas should be configured to allow connections.

To configure this, the DBA should run the following script:

ALTER AVAILABILITY GROUP [{ag_name}]
MODIFY REPLICA ON '{replica_name}'
WITH (SECONDARY_ROLE (ALLOW_CONNECTIONS = ALL, READ_ONLY_ROUTING_URL = 
'TCP://{replica_name}:{Port}'))

Configuring Replicate to access the AlwaysOn Listener

When working with AlwaysOn Availability Groups, you need to specify the IP address/host name and access credentials of the AlwaysOn Listener in the connection propertiesMicrosoft SQL Server source endpoint settings.

Limitations

DAG (Distributed Availability Groups) is not supported.

Accessing backup logs in AlwaysOn Availability Groups

As opposed to active transaction logs which are synchronized across the AlwaysOn Availability Group, backup transaction logs are different for each individual replica. Consequently, when Replicate needs to access the backup transaction logs, it "asks" each Replica in turn if it has the required logs, until the backup transaction logs are located. Note that if one of the Replicas that Replicate is trying to reach is offline, Replicate will wait until that Replica comes back online and then query it for the backup transaction logs.

Replicate needs to access the backup transaction logs on each Replica (or until it finds the required logs) in the following scenarios:

Working in backup only mode.

For more information on this mode, see Microsoft SQL Server source endpoint settings.
Starting a task from a specific timestamp.

For more information on this option, see the Tables are already loaded option in Advanced Run Options.
Due to latency i.e. if there is a high rate of events (changes) that Replicate is unable to process using the active log only.

Reading backup logs from AlwaysOn Availability Groups requires opening connections to all of the replicas. If you do not want to do this, set the Change processing mode in the Advanced tab to Online Logs only.

Setting up a non-sysadmin user when working with AlwaysOn availability groups

This section explains how to support a non-sysadmin user when working with AlwaysOn availability groups. For information on setting up non-sysadmin in a standard environment, see Setting up a non-sysadmin user in a standalone environment.

To support a non-sysadmin user when working with AlwayOn availability groups:

Set up Microsoft SQL Server for Replication as described in Setting up Microsoft SQL Server for replication.
Enable MS-REPLICATION on the source database. This can either be done manually or by running the task once using a sysadmin user.

Information note
MS-REPLICATION distributor should either be configured as local or in a way that allows access to non-sysadmin users via the associated linked server.

If the Exclusive automatic truncation endpoint option is enabled, stop the MS-REPLICATION Log Reader job.

On each replica perform the following steps (a-l):

Create schema [attrep] in the Master DB.

Create the table valued function [attrep].[split_partition_list] on the Master database, as follows:

USE [master]
GO

set ansi_nulls on
go

set quoted_identifier on
go

if (object_id('[attrep].[split_partition_list]','TF')) is not null
drop  function [attrep].[split_partition_list];
go

create function [attrep].[split_partition_list] 
( 
@plist varchar(8000),	--A delimited list of partitions	
@dlm nvarchar(1)	--Delimiting character
) 
returns @partitionsTable table --Table holding the BIGINT values of the string fragments
(
pid bigint primary key
) 
as 
begin
declare @partition_id bigint;
declare @dlm_pos integer;
declare @dlm_len integer;

set @dlm_len = len(@dlm);

while (charindex(@dlm,@plist)>0)
begin 
set @dlm_pos = charindex(@dlm,@plist);
set @partition_id = cast( ltrim(rtrim(substring(@plist,1,@dlm_pos-1))) as bigint);
insert into @partitionsTable (pid) values (@partition_id)
set @plist = substring(@plist,@dlm_pos+@dlm_len,len(@plist));
end 
set @partition_id = cast (ltrim(rtrim(@plist)) as bigint);
insert into @partitionsTable (pid) values (  @partition_id  );
return
end
GO

Create procedure [attrep].[rtm_dump_dblog] on the Master database, as follows:

USE [master]
GO

use [MASTER] 
go 

if (object_id('[attrep].[rtm_dump_dblog]','P')) is not null
drop procedure [attrep].[rtm_dump_dblog]; 
go

set ansi_nulls on
go 

set quoted_identifier on 
go
							
create procedure [attrep].[rtm_dump_dblog]
(
@start_lsn        varchar(32),
@seqno            integer,
@filename         varchar(260),
@partition_list        varchar(8000), -- A comma delimited list: P1,P2,... Pn
@programmed_filtering integer,
@minPartition     bigint,
@maxPartition     bigint
) 
as begin

        declare @start_lsn_cmp varchar(32); -- Stands against the GT comparator

        SET NOCOUNT ON  -- Disable "rows affected display"

        set @start_lsn_cmp = @start_lsn;
        if (@start_lsn_cmp) is null
                set @start_lsn_cmp = '00000000:00000000:0000';

        if (@partition_list is null)
        begin
                RAISERROR ('Null partition list waspassed',16,1);
                return
                --set @partition_list = '0,';    -- A dummy which is never matched
        end

        if (@start_lsn) is not null
                set @start_lsn = '0x'+@start_lsn;

if (@programmed_filtering=0)
        SELECT
                [Current LSN],
                [operation],
                [Context],
                [Transaction ID],
                [Transaction Name],
                [Begin Time],
                [End Time],
                [Flag Bits],
                [PartitionID],
                [Page ID],
                [Slot ID],
                [RowLog Contents 0],
                [Log Record],
                [RowLog Contents 1] -- After Image
        FROM
                fn_dump_dblog (
                        @start_lsn, NULL, N'DISK', @seqno, @filename,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default)
        where [Current LSN] collate SQL_Latin1_General_CP1_CI_AS > @start_lsn_cmp collate SQL_Latin1_General_CP1_CI_AS -- This aims for implementing FN_DBLOG based on GT comparator.
        and
        (
          (  [operation] in ('LOP_BEGIN_XACT','LOP_COMMIT_XACT','LOP_ABORT_XACT') )
          or
          (  [operation] in ('LOP_INSERT_ROWS','LOP_DELETE_ROWS','LOP_MODIFY_ROW')
                and
                ( ( [context]   in ('LCX_HEAP','LCX_CLUSTERED','LCX_MARK_AS_GHOST') ) or ([context] = 'LCX_TEXT_MIX') )
                and       [PartitionID] in ( select * from master.attrep.split_partition_list (@partition_list,','))
          )
          or
          ([operation] = 'LOP_HOBT_DDL')
        )
else
        SELECT
                [Current LSN],
                [operation],
                [Context],
                [Transaction ID],
                [Transaction Name],
                [Begin Time],
                [End Time],
                [Flag Bits],
                [PartitionID],
                [Page ID],
                [Slot ID],
                [RowLog Contents 0],
                [Log Record],
                [RowLog Contents 1] -- After Image
        FROM
                fn_dump_dblog (
                        @start_lsn, NULL, N'DISK', @seqno, @filename,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default,
                        default, default, default, default, default, default, default)
        where [Current LSN] collate SQL_Latin1_General_CP1_CI_AS > @start_lsn_cmp collate SQL_Latin1_General_CP1_CI_AS -- This aims for implementing FN_DBLOG based on GT comparator.
        and
        (
          (  [operation] in ('LOP_BEGIN_XACT','LOP_COMMIT_XACT','LOP_ABORT_XACT') )
          or
          (  [operation] in ('LOP_INSERT_ROWS','LOP_DELETE_ROWS','LOP_MODIFY_ROW')
                and
                ( ( [context]   in ('LCX_HEAP','LCX_CLUSTERED','LCX_MARK_AS_GHOST') ) or ([context] = 'LCX_TEXT_MIX') )
                and           ([PartitionID] is not null) and ([PartitionID] >= @minPartition and [PartitionID]<=@maxPartition)
          )
          or
          ([operation] = 'LOP_HOBT_DDL')
        )
        SET NOCOUNT OFF -- Re-enable "rows affected display"

end
GO

Create certificate on Master DB:

Use [master]
Go
CREATE CERTIFICATE [attrep_rtm_dump_dblog_cert]
ENCRYPTION BY PASSWORD = N'choose_your_own_pwd'
WITH SUBJECT = N'Certificate for FN_DUMP_DBLOG Permissions';

Create login from the certificate as follows:

Use [master]
Go
CREATE LOGIN attrep_rtm_dump_dblog_login FROM CERTIFICATE
[attrep_rtm_dump_dblog_cert];

Add the login to the sysadmin server role as follows:

ALTER SERVER ROLE [sysadmin] ADD MEMBER [attrep_rtm_dump_dblog_login];

Add the signature to [master].[attrep].[rtm_dump_dblog] by the certificate as follows:
```
Use [master]
GO
ADD SIGNATURE
TO [master].[attrep].[rtm_dump_dblog]
BY CERTIFICATE [attrep_rtm_dump_dblog_cert]
					WITH PASSWORD = 'choose_your_own_pwd';
```
Information note
If the stored procedure is recreated, you need to add the signature again.

Create procedure [attrep].[rtm_position_1st_timestamp] on the Master database, as follows:

use [master]
if object_id('[attrep].[rtm_position_1st_timestamp]','P') is not null
DROP PROCEDURE [attrep].[rtm_position_1st_timestamp];
go
create procedure [attrep].[rtm_position_1st_timestamp]
(
@dbname                sysname,      -- Database name
@seqno                 integer,      -- Backup set sequence/position number within file
@filename              varchar(260), -- The backup filename
@1stTimeStamp          varchar(40)   -- The timestamp to position by
) 
as begin

SET NOCOUNT ON       -- Disable "rows affected display"

declare @firstMatching table
(
cLsn varchar(32),
bTim datetime
)

declare @sql nvarchar(4000)
declare @nl                       char(2)
declare @tb                       char(2)
declare @fnameVar                 nvarchar(254) = 'NULL'

set @nl  = char(10); -- New line
set @tb  = char(9)   -- Tab separator

if (@filename is not null)
set @fnameVar = ''''+@filename +''''

set @sql='use ['+@dbname+'];'+@nl+
'select top 1 [Current LSN],[Begin Time]'+@nl+
'FROM fn_dump_dblog (NULL, NULL, NULL, '+ cast(@seqno as varchar(10))+','+ @fnameVar+','+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default,'+@nl+
@tb+'default, default, default, default, default, default, default)'+@nl+
'where operation=''LOP_BEGIN_XACT''' +@nl+
'and [Begin Time]>= cast('+''''+@1stTimeStamp+''''+' as datetime)'+@nl

--print @sql
delete from  @firstMatching 
insert into @firstMatching  exec sp_executesql @sql    -- Get them all

select top 1 cLsn as [matching LSN],convert(varchar,bTim,121) as [matching Timestamp] from @firstMatching;

SET NOCOUNT OFF      -- Re-enable "rows affected display"

end
GO

Create certificate on Master DB:

Use [master]
Go
CREATE CERTIFICATE [attrep_rtm_position_1st_timestamp_cert]
ENCRYPTION BY PASSWORD = N'choose_your_own_pwd'
WITH SUBJECT = N'Certificate for FN_POSITION_1st_TIMESTAMP Permissions';

Create login from the certificate as follows:

Use [master]
Go
CREATE LOGIN attrep_rtm_position_1st_timestamp_login FROM CERTIFICATE
[attrep_rtm_position_1st_timestamp_cert];

Add the login to the sysadmin server role as follows:

ALTER SERVER ROLE [sysadmin] ADD MEMBER [attrep_rtm_position_1st_timestamp_login];

Add the signature to [master].[attrep].[rtm_position_1st_timestamp] by the certificate as follows:
```
Use [master]
GO
ADD SIGNATURE
TO [master].[attrep].[rtm_position_1st_timestamp]
BY CERTIFICATE [attrep_rtm_position_1st_timestamp_cert]
WITH PASSWORD = 'choose_your_own_pwd';
```
Information note
If the stored procedure is recreated, you need to add the signature again.

Create a user with the following permissions/roles (in each of the following databases):

Information note
The login should be created with the same SID on each replica.
- Master DB (on each replica) :
  - select on sys.fn_dblog
  - view any definition
  - view server state (should be granted to the login).
  - execute on sp_repldone
  - execute on sp_replincrementlsn
  - execute on sp_addpublication
  - execute on sp_addarticle
  - execute on sp_articlefilter
  - select on [attrep].[split_partition_list]
  - execute on [attrep].[rtm_dump_dblog]
  - execute on [attrep].[rtm_position_1st_timestamp]
- MSDB DB (on each replica):
  - select on msdb.dbo.backupset
  - select on msdb.dbo.backupmediafamily
  - select on msdb.dbo.backupfile
- For the source database (as the database is synchronized, it can be done on the primary replica only):
  - db_owner ROLE

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