I've got SQL2012 running on 2 different servers with public, static IP addresses. I want to implement replication in a way that will keep both servers in sync at all times, regardless of which server is actually receiving the data. I've been reading about the subscriber/publisher model but I'm not exactly sure which should be which. A few facts about our setup:
I'm trying to achieve failover. If server A goes down, I need server B to be operational and have all latest data, or as close as possible. And vice versa. When the server comes back online, I need the replication to get caught up quickly and start working again. I need failures to be graceful, in other words I can't have server A get weird just because server B went offline.
I don't need realtime replication, but close would be nice. If server A was 10 seconds behind server B with data updates, nobody would care. But if it were an hour behind, that would be bad. Fast DB performance is more important that realtime replication, but again, close would be nice.
My database is just shy of 900Mb, and grows by 3Mb per day.
I am looking for advice on the best way to set this up given my setup and needs. Much appreciated.
Since one server will be Primary and the other Failover, use Log Shipping. It will keep two databases the same for all transactions completed on Primary server upto the failure moment. All transactions that have not completed at the moment of failure, will not appear on Failover server, so they should resubmitted by the application and hit Failover server.
Also there should be a Recovery procedure, to ensure than Primary server is up to date.
Useful articles:
Database Mirroring and Log Shipping.
Configure Log Shipping
Related
I have installed SQL server database (mainserver) in one instance and SQL server database for RerportServer in others. what is the best way to replicate data from mainServer to report Server? Data in mainServer changes frequently and actual information in the ReportSever is very important.
And there is many ways to do this:
mirroring
shipping log
transactional replication
merge replication
snapshot replication
are there some best-practices about this?
Thanks
You need Transactional Replication for your case. Here is why you would not need the other 4 cases:
Mirroring
This is generally used to increase the availability of a database server and provides for automatic failover in case of a disaster.
Typically even though you have more than a single copy of the database (recommended to be on different server instances), only one of them is active at a time, called the principle server.
Every operation on this server instance is mirrored on the others continuously (as soon as possible), so this doesn't fit your use case.
Log Shipping
In this case, apart from the production database servers, you have extra failover servers such that the backup of the production server's database, differential & transactional logs are automatically shipped (copied) to the failovers, and restored.
The replication here is relatively scheduled to be at a longer interval of time than the other mechanisms, typically ranging from an hour to a couple of hours.
This also provides for having the failver servers readies manually in case of a disaster at the production sites.
This also doesn't fit your use case.
Merge Replication
The key difference between this and the others is that the replicated database instances can communicate to the different client applications independent of the changes being made to each other.
For example a database server in North America being updated by clients across Americas & Europe and another one in Australia being updated by clients across the Asia-Pacific region, and then the changes being merged to one another.
Again, it doesn't fit your use case.
Snapshot Replication
The whole snapshot of the database is published to be replicated to the secondary database (different from just the log files being shipped for replication.)
Initially however, for each type of replication a snapshot is generated to initialized the subscribing database, i.e only once.
Why you should use Transactional Replication?
You can choose the objects (Tables, Views, etc) to be replicated continuously, so if there are only a subset of the tables which are used to reporting, it would save a lot of bandwidth. This is not possible in Mirroring and Log Shipping.
You can redirect traffic from your application to the reporting server for all the reads and reports (which you can also do in others too, btw).
You can have independent batch jobs generating some of the more used reports running on the reporting server, reducing the load on the main server if it has quite frequent Inserts, Updates or Deletes.
Going through your list from top to bottom.
Mirroring: If you mirror your data from your mainServer to your reportServer you will not be able to access your reportServer. Mirroring puts the mirrored database into a continuous restoring state. Mirroring is a High Availability solution. In your case the reportServer will only be available to query if you do a fail over. The mirrored server is never operational till fail over. This is not what you want as you cannot use the reportServer till it is operational.
Log Shipping: Log shipping will allow you to apply transactional log backups on a scheduled event to the reportServer. If you backup the transaction log every 15 minutes and apply the data to the reportServer you will have a delay of 15+ minutes between your mainServer and Log server. Mirroring is actually real time log shipping. Depending on how you setup log shipping your client will have to disconnect while the database is busy restoring the log files. Thus during a long restore it might be impossible to use reporting. Log Shipping is also a High Availability feature and not really useful for reporting. See this link for a description of trying to access a database while it is trying to restore http://social.msdn.microsoft.com/forums/en-US/sqldisasterrecovery/thread/c6931747-9dcb-41f6-bdf4-ae0f4569fda7
Replication : I am lumping all the replication together here. Replication especially transactional replication can help you scale out your reporting needs. It would generally be mush easier to implement and also you would be able to report on the data all of the time where in mirroring you cant report on the data in transaction log shipping you will have gaps. So in your case replication makes much more sense. Snapshot replication would be useful if your reports could be say a day old. You can make a snapshot every morning of the data you need from mainServer and publish this to the subscribers reportServer. However if the database is extremely large then Snapshot is going to be problematic to deal with on a daily basis. Merge replication is only usefull when you want to update the replicated data. In your case you want to have a read only copy of the data to report on so Merge replication is not going to help. Transactional Replication would allow you to send replications across the wire. In your case where you need frequently updated information in your reportServer this would be extremely useful. I would probably suggest this route for you.
Just remember that by implementing the replication/mirroring/log shipping you are creating more maintenance work. Replication CAN fail. So can mirroring and so can transaction log shipping. You will need to monitor these solutions to make sure they are running smoothly. So the question is do you really need to scale out your reports to another server or maybe spend time identifying why you cant report on the production server?
Hope that helps!
I'm not a DBA so this may be a stupid question but I'll ask it anyway. We're upgrading our SQL Servers from 2000 to 2005 and we will probably use either database replication or database mirroring. Our DBA would like to "multipurpose" the standby server meaning that he'd like to increase our capabilities and capacity by running other database applications on the standby server since "it's just going to be sitting there anyway" (his words, not mine). Is this such a good idea? Right now, our main application server uses only one instance that contains 50+ databases. As I understand it, what we're doing now and what our DBA is proposing for a failover server is a bad idea because all of these databases are sharing memory, CPUs, and working areas. If one applications starts behaving badly, the other DBs could be affected.
Any thoughts?
It's really a business question that needs to be answered?? is a slow app better then no app if you can't afford the expense of extra hardware?
Standby and mirrored db's can be used for reporting. Using it as the failover db can work if you have enough headroom (i.e. both databases will comfortably run on the server)
Will you depend on these extra applications? Where do they run in the failover case?
You really need to understand your failure modes.
If you look at it as basic resource math, that doesn't often make sense unless the resources you have running in the failure scenarios can handle the entire expected load. Sometimes this is the case, but not always. In this case, to handle the actual load you may need yet another server to come in (like RAID - perhaps your load needs a minimum of 5 servers, but you have a farm of 6, then you need 1 standby server for ever server to fail above 1). Sometimes a farm can run degraded, but sometimes they just puke and die.
And in the case of out of normal operation, you often have accident cascading where a legitimate incident causes a cascade of issues - e.g. your backup tape is busy restoring a server from a backup (to a test environment, even - there are no real "failures"), now your sql server or exhcange server (or both) is not backed up and your log gets full.
Database Mirroring would not be the way to go here in my opinion as it provides redundancy at the database level only. So you would need to configure database mirroring for up to 50 databases based on the information you provided. The chances are that if one DB where to fail all, 50 would probably follow, as failures typically occur at the hardware level rather than a specific database.
It sounds to me like you should be using SQL Server Clustering technology. You could create an Active/Active cluster to support your requirements.
What is an Active/Active Cluster?
An Active/Active SQL Server cluster means that SQL Server is running on both nodes of a two-way cluster. Each copy of SQL Server acts independently, and users see two different SQL Servers. If one of the SQL Servers in the cluster should fail, then the failed instance of SQL Server will failover to the remaining server. This means that then both instances of SQL Server will be running on one physical server, instead of two.
Applying this to your scenario
You could then split the databases between two instances of SQL server, one active instance on each node. Should one node fail, the other node will pick up the slack and vice versa.
Further Reading
An introduction to SQL Server Clustering
I suspect that you will find the following MSDN thread useful reading also
"it's just going to be sitting there anyway"
It will be sitting there applying transactions...
Take note of John Sansom's recommendation. Keep in mind that a Active/Active cluster requires two sql server licenses and a failover cluster/mirror only needs one.
Setting up mirroring for a large number of db's could turn into a big pain. You need any jobs/maintenance to move over as well - which can be achieved with alerts on WMI failover events. There's probably more to think about that could complicate things.
Hi can any body tell me what is use of replication in sqlserver2005.
backup and replicaton looks same?what is diference b/w them
Backups are exactly that: backups. They enable you to recover the data if something bad happens.
Replication is another beast entirely. It basically distributes the data across multiple nodes so that each node has a complete, (close to) up-to-date copy of the data.
There are a number of reasons why you would use replication including, but not limited to:
High availability so that, if one node goes down, other nodes can still service requests.
Geographical distribution, meaning your data can be placed close to those that need it. Clients in Belarus don't need to go all the way to Montana to get the data if you maintain a local replica in Belarus (or somewhere close) - this is for performance. You may have 10,000 clients in Belarus - it's quicker to send one copy over than have all 10,000 request data [although this depends on how often they request data].
Prioritization. If your reporting users (bank management) have a lower service level agreement than your customer-facing staff (bank tellers) [and they should], you can put all the management onto a replica so as not to slow down the primary copy.
Replication is used for a different purpose, for example to make reports without putting that load on the 'real' database.
Replication increases system availability. If one set of database is down, you can serve out of replica.
Backup saves you from catastrophic errors such as human error that dropped the production database. Note that in this case, replication won't save you as it will dutifully replicate drop command.
SQL Server replication is the process of distributing data from a source database to one or more destination databases throughout the enterprise.
Replication is a great solution for maintaining a reporting server.
Clients at the site to which the data is replicated experience improved performance because those clients can access data locally rather than connecting to a remote database server over a network.
Clients at all sites experience improved availability of replicated data. If the local copy of the replicated data is unavailable, clients can still access the remote copy of the data.
Replication: Lots of data, fast and most recent.
Backup/Restore: Some data, perhaps a bit slower, and a specific point in time.
Replication can be used to address a number of different scenarios as detailed below.
Just to be clear however, Replication is not the same as Database Backup
Scenarios:
Server to server: Replicating Data in a Server to Server Environment
Improving Scalability and Availability
Data Warehousing and Reporting
Integrating Data from Multiple Sites(Server)
Integrating Heterogeneous
Data Offloading Batch Processing
Server to client: Replicating Data Between a Server and Clients
Exchanging Data with Mobile Users
Consumer Point of Sale (POS)
Applications Integrating Data from
Multiple Sites (Client)
For a full overview of Microsoft SQL Server Replication see the following Microsoft reference.
http://msdn.microsoft.com/en-us/library/ms151198(SQL.90).aspx
Choose the track that is most appropriate to you (i.e. Developer / Architect) and all shall be revealed :-)
I have two database servers running SQL Server 2005 Enterprise that I want to make one of them as mirror database server.
What I need is; to create an exact copy database from primary server on mirror server, so when the primary server was down, we could switch database IP on application to use mirror server.
I have examined "mirror" feature on SQL Server 2005, and based on this article:
http://aspalliance.com/1388_Database_Mirroring_in_Microsoft_SQL_Server_2005.all
The mirror database cannot be accessed directly; however snapshots of the mirror database can be taken for read only purposes. (Prerequisites no. 4)
So how it can be useful when I can't access it when primary server was down?
I've been thinking about creating a regular backup on primary server and restore it on mirror server on hourly basis, but that's quite inefficient (slow) especially if I want an exact copy (since hundreds data's are added once in minute).
Any other suggestion?
EDIT:
Maybe what I mean was a replication thing, not a mirror (thanks JP for commenting)
They are referring to the fact that you can't perform queries on the mirrored copy, but you can get around that limitation by creating a snapshot of the mirrored database. This is often done to create a read-only database copy for reporting uses. You would have full access of the mirror if the primary were to fail, but it will not failover automatically.
Log shipping is another option, which allows you to query (read-only) the standby database without having to create a snapshot.
If I understand your question correctly, you shouldn't have to do that. There are several role switching forms you can use to have your mirror take over as primary. You don't change the IP address at the application level, the cluster itself has a virtual IP address that allows access to the data at any given time (given a reasonable amount of time for the switch over to the mirror from a primary failure). The mirror stays in synch by itself. :) There are good articles here and here on clustering.
Edit: Okay, based on the comments, check out the various options for replication.
Your confusion is common - there's a lot of ways to do disaster recovery planning with SQL Server. I've recorded a 10-minute video tutorial of SQL Server disaster recovery options including log shipping, mirroring, replication and more. If you like that one, we've got a longer one at Quest called Disaster Recovery Techniques but that one requires registration.
Instead of investigating a specific technology here, what you might want to do is tell us what your needs are, and then we can help you find out what option is right for you. The videos will give you an idea of what kinds of information you need to know before selecting a particular solution.
When using only two SQL Servers, you need to do the fail-over manually. The 'backup' database will be usable after you do two things;
Disable mirroring on it
Restore the database with RECOVERY (but without a backup file, this will make the database usable).
Therefore mirroring in this manner does make scense, however it is hard to maintain;
Moving back from the backup database to the primary is a 'pain' as you have to set-up the complete mirroring again using a backup of the redundant server. This is needed to get the primary back up to speed.
My recommendation would be to get a thrid SQL Server into the picture that can act as a witness. The witness will monitor the status of the mirroring databases. Your bonus; you will get automatic failover, and will not have the fail-over (and after fail-over) issues.
If I remeber correct, the witness server can be running SQL Express so no need for the Enterprise version on all three - just the two where the actual mirroring will take place.
Let me know if you need Transact SQL for the commands to fail-over and 'anti-fail-over' in a two server scenario, and I can dig them up.
I remember hearing Joel say he has 2 different locations where the servers are located, each location has 2 front end servers and 1 back end server.
If a one of the hosting facilities goes down, how can he switch over to the other one? (Or is it just going to be a DNS change that will take 24-72 hours to propagate?).
How can a single SQL Server instance have so many databases on it? FB has a completely separate database per account. I can't see a single SQL Server instance having more than say 200-250 databases on it! And I'm sure they have more customers than that.
They talked about this in one of the Stack Overflow podcasts, but I can't find it in the transcripts.
1) Each of the two centers handles approximately 1/2 of the users. Fairly often (hourly, I think Joel said) they ship transaction logs to the other site. If site A goes down, they bring up the db backups on site B, and do the DNS switchover. It won't be instantaneous or automated, nor do they want it to be, because they'll be coming up with slightly stale data, and want to avoid that if it's at all possible to bring the broken site back up.
I'm not sure how they handle the DNS situation, but you can set the TTL on DNS records to mere seconds to limit caching, and have failover occur very quickly.
2) Why not? I'm not sure of the hard limit of databases per instance, but there's also nothing keeping you from running multiple instances of SQL Server on your box. I would imagine you're more limited by hardware than software. (You can also run Fogbugz with a MySQL database backend).
Got a few questions in here so I'll break these out:
If a one of the hosting facilities goes down, how can he switch over to the other one?
There's several ways to do this, including database mirroring (new in SQL Server 2005), log shipping, and replication. I've recorded a podcast on SQL Server high availability and disaster recovery options at SQLServerPedia.
(Or is it just going to be a DNS change that will take 24-72 hours to propagate?)
Like the other post mentioned, you can set your DNS time-to-live numbers very slow, but the cooler method uses database mirroring. With mirroring, you can set both the primary and secondary server names in your connection string, and your application will automatically try the second server when the first one doesn't respond.
How can a single SQL Server instance have so many databases on it? FB has a completely separate database per account. I can't see a single SQL Server instance having more than say 200-250 databases on it! And I'm sure they have more customers than that.
The largest SQL Server I've worked with had over a thousand databases, and I've talked to a couple of other DBAs who have worked on systems with more than 2,000 databases on a server. It certainly makes management much more challenging, that's for sure.