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High availability Archives - Page 3 of 7 - Blog dbi services

David Barbarin

SQL Server AlwaysOn availability groups and statistic issues on secondaries

By | Database Administration & Monitoring | 3 Comments

I would like to share with you an interesting issue you may face while using SQL Server AlwaysOn availability groups and secondary read-only replicas. For those who use secondary read-only replicas as reporting servers, keep reading this blog post because it is about update statistics behavior on the secondary replicas and as you may know cardinality estimation accuracy is an important part of the queries performance in this case. So a couple of days ago,…

 
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David Barbarin

SQL Server 2016: Distributed availability groups and Cross Cluster migration

By | Database Administration & Monitoring | 2 Comments

How to migrate an environment that includes availability groups from one Windows Failover Cluster to another one? This scenario is definitely uncommon and requires a good preparation. How to achieve this task depends mainly of your context. Indeed, we may use a plenty of scenarios according to the architecture in-place as well as the customer constraints in terms of maximum downtime allowed for example. Among all possible scenarios, there is a process called “cross-cluster migration…

 
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David Barbarin

SQLSaturday #546 Porto – Troubleshooting scenarios with availability groups

By | Database management, Technology Survey | No Comments

J-1 before the next SQL Saturday 2016 in Portugal. I usually promote this event in France but this time this is for SQL Server Portuguese community. I will have the chance to talk about SQL Server AlwaysOn and troubleshooting scenarios. It will be also a good opportunity to meet portuguese people like Niko Neugebauer (@NikoNeugebauer), André Batista (@klunkySQL) and many others. Moreover, Porto is definitely a beautiful city and a good way to finish the summer…

 
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David Barbarin

SQL Server AlwaysOn: troubleshooting improvements with new service packs

By | Database Administration & Monitoring | No Comments

As promised in my latest blog, I will talk about improvements in the detection of the availability group replication latency. As a reminder, replication latency between high available replicas may be monitored in different manners so far. Firstly, in my experience I had the opportunity to use different performance counters as “Database Replica:Transaction Delay” and “Databas Replica:Mirrored Write Transactions/sec” in order to get a good picture of the latency over the time after implementing an…

 
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David Barbarin

SQL Server 2016 AlwaysOn: distributed availability groups

By | Database Administration & Monitoring | No Comments

This time, I will talk about distributed availability groups. What’s that? In short, a group of availability groups. Sounds good right? But in which cases may we need such architecture? Firstly, let’s say that distributed availability groups will run on the top of two distinct availability groups meaning that they reside on two distinct WSFCs with their own quorum and voting management. Referring to the Microsoft documentation here, we may think that this new feature…

 
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David Barbarin

SQL Server AlwaysOn: is my database ready for failover?

By | Database Administration & Monitoring | No Comments

In this blog post I just want to clarify values that we may find from the is_failover_ready column of the sys.dm_hadr_database_replica_cluster_states DMV. A couple of days ago, I had an interesting discussion with one of my customers during which he explained he was not confident about the availability group state after facing some unavailability issues. The main source of uncertainty was the result from the following query that he used to check if everything was…

 
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David Barbarin

Windows Failover Cluster : Introduction to paxos tag

By | Database Administration & Monitoring, Operation systems | No Comments

A couple of days ago, I was in charge to install a new SQL Server AlwaysOn and availability group with one of my colleague Nathan Courtine. During the installation, we talked about testing a disaster recovery scenario where we have to restart the Windows Failover cluster in forced quorum mode. Restarting a WSFC in such mode implies some internal stuff especially for the cluster database data synchronization between nodes. The WSFC uses internally the paxos…

 
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David Barbarin

Windows Server 2016: Introducing stretch cluster functionality

By | Database Administration & Monitoring, Hardware & Storage | One Comment

Let’s continue with the new high available functionality shipped with the next Windows version. In my previous blog, I talked about the new site awareness feature that provides more flexibility to configure failover resources priorities and more granular heartbeat threshold as well by introducing the new site concept. This time, we’ll talk about stretch cluster. What’s that? Let’s introduce the concept with some customer experiences for which we introduced high availability with the implementation of…

 
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David Barbarin

SQL Server AlwaysOn: when a listener becomes the cluster and vice versa

By | Database Administration & Monitoring, Database management | No Comments

Let’s talk about a funny story that concerns an interesting issue that I faced a couple of months ago at one of my customers. Initially, the problem concerned only the creation of an availability group listener but after deleting the related availability group, he noticed quickly that the deletion failed but even more strange, he noticed that the virtual network name related to the listener corresponded to the virtual computer object of the cluster itself….

 
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Daniel Westermann

The dbi services PostgreSQL reference architecture (2) – The community approach

By | Database Administration & Monitoring | No Comments

In the last post I looked at how dbi services designs a PostgreSQL architecture based on the products of EnterpriseDB. In this post I’ll look at the same questions but using pure community tools. If you do not need vendor support and do trust the community for providing help and fixes this is another way to go. And usually you can trust the community around PostgreSQL very well. The architecture itself is pretty much the…

 
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