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Interesting one today:

This is Part 2 on blogs related to Replication Setup. Full list is here.

In a recent post, we walked through the steps for setting up replication using T-SQL commands. Today, we’ll look at the commands to remove/drop replication
using T-SQL commands.

Essentially there are 3 major steps to dropping replication; And all steps are executed at Publisher instance. As and when needed, these steps will communicate with Subscriber & Distributor to remove relevant artifacts at each step.

Main Steps:

  1. Remove definitions for Publication, Subscription & all relevant articles
  2. Change database settings
  3. Change Distributor settings

As expected, each of these major steps could have multiple sub-steps, which we’ll get into in future posts.

NOTE: All steps are carried out at Publisher instance

Replication Step T-SQL Step
1. Remove Publication, Subscriptions, etc

a. Remove subscription to each subscriber

b. Remove subscription with articles

c. Remove articles associated with the publication

d. Finally, remove the Publication

1. Run Publisher Instance

a. sp_dropsubscription

b. sp_dropsubscription

c. sp_droparticle

d. sp_droppublication

2. Change database settings

a. Disable database from Publishing

b. Remove associations with all Subscribers

2. Run at Publisher

a. sp_replicationdboption

b. sp_dropsubscriber

3. Distributor Settings

a. Remove association with Distributor

3. Run at Publisher

a. sp_dropdistributor

In a future post, we’ll get into the next set of details.

Hope this helps,
_Sqltimes

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Interesting one today:

This is part of the series on Replication set up using T-SQL. The full list is here.

Today, we’ll go over setting up Distributor using T-SQL. This is the first step in our replication configuration process.

The major steps in setting up Distributor are:

  1. Configure an instance as Distributor
  2. Create Distributor database
  3. Add the instances that will use this instance as a distributor

For this example, we’ll move forward with remote distributor a.k.a. Publisher, Subscriber & Distributor are on dedicated instances.

To accomplish the above steps, we use the following T-SQL procedures:

  1. sp_adddistributor
  2. sp_adddistributiondb
  3. sp_adddistpublisher

1. sp_adddistributor

For setting up replication, the first step we need to configure is setting up Distributor. Go to the Distributor instance, and enable the instance as a Distributor.

--
-- Enable the instance as Distributor
--
use master
exec sp_adddistributor    @distributor = N'InstanceName'
	 					, @password = N'distributor_admin password'
GO

2. sp_adddistributiondb

Next step is to create Distribution database in the Distributor instance to hold all the replication traffic.

--
-- Create Distribution database
--
use master
exec sp_adddistributiondb @database = N'SalesDistribution'
			, @data_folder = N'E:\MSSQL\Data'
			, @data_file = N'SalesDistribution.mdf'
			, @data_file_size = 4096
			, @log_folder = N'E:\MSSQL\Data'
			, @log_file = N'SalesDistribution.LDF'
			, @log_file_size = 2048

			, @min_distretention = 0
			, @max_distretention = 120
			, @history_retention = 120

			, @security_mode = 1
GO

Most of the parameters are self-explanatory; So, we’ll look at brief descriptions.

Following set of parameters indicate the name of the Distribution database with location for its data & log files with initial sizes.

    •  @database
    • @data_folder
    • @data_file
    • @data_file_size
    • @log_folder
    • @log_file
    • @log_file_size

The next set of parameters, indicate the duration for retention of replication traffic (transactions & commands) and retention for history log entries.

    • @min_distretention
    • @max_distretention
    • @history_retention

The last parameter, shows the authentication mechanism for communicating with the Distributor.

  • @security_mode : 1 indicates Windows Authentication; 0 indicates Sql Authentication (default)

3. sp_adddistpublisher

Now that Distribution database is configured, lets inform the distributor about the Publishers that it will rely on it (this Distributor).

--
-- Associate Distributor with Publishers
--
exec sp_adddistpublisher  @publisher = N'PublisherName'
			, @distribution_db = N'SalesDistribution'
			, @publisher_type = N'MSSQLSERVER'
			, @working_directory = N'E:\MSSQL\ReplData'

			, @security_mode = 1
			, @thirdparty_flag = 0
GO

The first four parameters indicate the name of the Publisher instance; And if it is Sql Server Publisher (or Oracle, etc); Working directory indicates where the replication data is stored while being communicated between Publisher and Distributor; And the name of the Distribution database.

    •  @publisher
    • @distribution_db
    • @publisher_type
    • @working_directory

The next two parameters indicate the authentication mechanism used by Replication Agents to communicate with Publisher (for Queued Updating Subscriptions); And

    • @security_mode
    • @thirdparty_flag : Indicates if Publisher is Sql Server or non-Sql Server instances (i.e. Oracle, etc)
Hope this helps,
_Sqltimes

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Interesting one today:

This is Part 1 on blogs related to Replication Setup. Full list is here.

Quite often, we setup replication on our lab machines to replicate production environment settings. We have one “Gold” version of scripts that are used every time. Today, w’ll cover the fundamental procedures & their related stored procedures:

Create Replication

Essentially, there are 4 fundamental steps to creating replication. Some steps are carried out pointed to Distribution instance, some pointed to Publisher instance; But there are no steps pointed to Subscriber instance.

  1. Configure an instance as Distributor
  2. Configure an instance as Publisher
  3. Configure a database as Publisher & Create Publication
  4. Configure Subscription

As you can imagine, there are several sub-steps in each of these. We’ll get into details about the sub-steps in a new post.

Replication Step T-SQL Stored Procedure
1.Distributor

a. Configure an instance as Distributor

b. Create Distributor database

c. Add the instances that will use this instance as a distributor

1. Run at Distributor instance

a. sp_adddistributor

b. sp_adddistributiondb

c. sp_adddistpublisher

2. Configure Publisher

a.  Configure the instance to be Distributor

b.  Configure the Subscribers

3. Configure Publisher Database & Publication

a. Enable the database as a Publisher

b. Create LogReader Agent

c. Configure publication

d. Assign permissions on this Publication

e. Add articles (tables, SP, etc)

4. Configure Subscription

a. Add subscribers for this publication

b. Create the distribution agent

2. Run at Publisher instance

a. sp_adddistributor

b. sp_addsubscriber

3. Run pointing to Publisher database

a. sp_replicationdboption

b. sp_addlogreader_agent

c. sp_addpublication

d. sp_grant_publication_access

e. sp_addarticle

4. Run pointing to Publisher database

a. sp_addsubscription

b. sp_addpushsubscription_agent

In a future post, we’ll get into the next set of details.

Hope this helps,
_Sqltimes

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Interesting one today:

As part of the series on Replication, we’ll cover Tracer Tokens topic today. Tracer Tokens is one of the techniques to measure the latency in replication topology; It is unique and a powerful way to measure the health and latency of replication set up.

Concept:

In replication, we have a Publisher, Distributor & Subscriber. Publisher has a Publication as the source of data to be replicated to Subscriber(s). Distributor helps in getting data from Publisher to Subscriber. In this topology, data is constantly flowing from Publisher to Distributor and eventually to all the Subscribers. At every step, as data flows through the topology, there is latency. Tracer Tokens helps in measuring this latency at each step.

Tracer tokens are dummy replication traffic inserted at the Publisher; As it flows through the topology, it captures the time it takes to arrive at each step (Distributor) and eventually to the destination (Subscriber). This BoL article has more details on this concept.

T-SQL to Insert Tracer Tokens

There are 4 main T-SQL procedures to managing Tracker Tokens:

  1. Insert tracer token at the Publisher
  2. Get a list of all tracer tokens
  3. Gather details on a given tracer token
  4. Delete tracer token history

Insert Tracer Token at Publisher

Connect to Publisher and point to the publisher database. Then run the ‘sp_posttracertoken‘ procedure with appropriate parameters to insert token into this particular publication. See the example below and the attached result.

@tokenID is the OUTPUT variable, that returns the ID of the token after successfully inserting at the Publisher.

--
-- Insert token at publisher
--
DECLARE @tokenID AS INT

EXEC sp_posttracertoken   @publication		= 'SamplePublication'
						, @tracer_token_id	= @tokenID OUTPUT

SELECT @tokenID AS [TokenID]
GO
Insert Tracer Token

Insert Tracer Token

Get a list of all tracer tokens

In situations, where we do not have the token Id readily available, we could query and get a list of all the tokens inserted with their IDs.

In SSMS, go to Distributor instance and point to the Distributor database and run ‘sys.sp_helptracertokens’ procedure with relevant parameters. See below:

--
-- Get the list of tokens already inserted
--
EXEC sys.sp_helptracertokens @publication	= 'SamplePublication'
							, @publisher	= 'ABC_Instance'
							, @publisher_db = 'SampleDatabase'

GO
List of Tracer Tokens

List of Tracer Tokens

 

Gather details on a given tracer token

Now this is the important procedure that shows us the latency numbers at each step of the replication topology. Open SSMS and point to Distribution instance and point to Distribution database and run ‘sys.sp_helptracertokenhistory’ procedure with pertinent parameters. Se below:

--
-- Query latency number gathered by a particular tracer token
--
EXEC sys.sp_helptracertokenhistory	  @publication = 'SamplePublication'
									, @publisher = 'ABC_Instance'
									, @publisher_db = 'SampleDatabase'
									, @tracer_id = -2147483574
GO
Latencies gathered from Tracer Token

Latencies gathered from Tracer Token

 

Delete tracer token history

Finally, removing the tokens from the metadata. Sql Server provides ‘sp_deletetracertokenhistory’ procedure to delete a given token from a publication. See below:

--
-- Delete a particular token
--
EXEC sp_deletetracertokenhistory  @publication = 'SamplePublication'
								, @publisher = 'ABC_Instance'
								, @publisher_db = 'SampleDatabase'
								, @tracer_id = -2147483573
GO
Delete Tracer Token

Delete Tracer Token

Hope this helps,
_Sqltimes

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Quick one today:

On a regular bases, on production machines, selected perfmon metrics are captured into local files. Each day’s metrics are captured into an individual file — making it easier to analyze the data as and when needed.

Sometimes, to uncover any patterns, we’d need to combine a few days worth of files into one BLG file. This is rare, but needed. Microsoft provides a command to achieve this action. Enter relog command. This command could do a lot of things, but today we’ll look at file concatenation.

relog SqlCounters_08112017_48.blg SqlCounters_08122017_49.blg -f BIN -o C:\PerfLogs\Sql2014Counters\1\s.blg

Explanation:

The following Perfmon files

  • SqlCounters_08112017_48.blg
  • SqlCounters_08122017_49.blg

are combined into a final binary file called Combined.blg.

  • -f flag indicates the format of the output (concatenated file)
  • -o flag indicated the path of the output file

The following image shows, the output when you run it from command prompt.

Concatenate_Perfmon_BLG

Hope this helps,
_Sqltimes

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Interesting one today:

During one of the Sql Cluster set up in our lab environment, we ran into this interesting (and common) error message.

The Sql Server failover cluster instance name '' already exists as a clustered resource. 
Specify a different failover cluster name.
Sql Cluster Set up Error

Sql Cluster Set up Error

Resolution

Turns out, the sysadmins created a Resource Group with the same name and allocated all the cluster disks to it. So, when I attempt to create a new Resource Group (for Sql Server resources), it throws this error.

 

SqlCluster Install Resolution

SqlCluster Install Resolution

 

Solution: Once the dummy resource group was removed, the cluster set up wizard progressed without any errors.

The moral of the story is, when we are about to create a resource group, make sure a resource group by the same name does not already exist.

 

 

Hope this helps,
_Sqltimes

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Interesting one today:

Lately, Access Methods performance metrics have been helpful in troubleshooting some recent issues. Access Methods has several important metrics that show the metrics to measure the usage internals of logical data with in Sql Server.

Here we’ll look at 3 of them:

  1. \SQLServer:Access Methods\FreeSpace Scans/sec
  2. \SQLServer:Access Methods\Table Lock Escalations/sec
  3. \SQLServer:Access Methods\Workfiles Created/sec

FreeSpace Scans

Objects in Sql Server are written on database pages. A group of these pages are called Extents (8 pages). Allocation of space occurs in units of extents. Extents are of two types Mixed & Uniform Extents.

Usually small tables (and sometimes Heap tables) are written to Mixed extents. So, when the data in those tables/objects increases, Sql Server needs to find more free space to  accommodate for the growth. In these situation, Sql Server performs Free Space Scans. This counter measure how many times these occur every second, hence FreeSpace Scans/sec.

Not sure what Microsoft’s recommended range on this metric is, but in our environment, this metric stays low i.e. under 5 or 10. So, as a rule of thumb, lets say as long as the number is below 20 we are okay. Anything higher for extended periods of time might need some attention.

So the best approach is to gather baseline first; Then you’ll know what is normal and what is out of the ordinary.

Table Lock Escalations

When a query is trying to read rows from a table, it uses the smallest lock as possible to maintain concurrency. In some rare (but not uncommon) occasions, this lock gets escalated higher level, either Page or Table level. While this reduces concurrency on that table, it improves the efficiency of this particular query execution.

Issuing thousands of locks costs a lot of memory; So it is easier to issue table lock and read as much data as needed. But the down side is that it will prevent other connections from reading this table.

For more, read this previous post on Lock Escalations.

This counter measures, the number of such escalations occur per second. Which this is a common occurrence, higher numbers for extended periods of time are not good. So, look into optimizing queries, so they only query the exact amount of data they need (a.k.a. use better JOINs and WHERE clause conditions)

Workfiles Created

When a large query that handles large data sets is executed, sometimes the intermediary data sets (or virtual tables) are written to disk. This helps with efficient processing of data. Sql Server reads this data into memory as and when needed and completes query processing.

This counter measures, how many work files are created each second. On a busy system, that handles large data set manipulation queries, many WorkFiles & WorkTables are created each second. So, this number needs to be considered in context. Capture a baseline first; Then measure any aberrations from baseline and look into possible reasons.

Usually when a query manipulates large data sets, Sql Server uses Hash Joins to manipulate the data to find matches. So, if you have a lot of queries that perform Hash Joins or Hash Aggregates, this counter spikes up.

 

Hope this helps,
_Sqltimes

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