When you connect to Secondary Replica, but it has not been enabled for read workload, you will get the following error under two situations (1) You connect directly to one of the databases under availability group. It is denied because the database is not enabld for read workload. (2) You connect to a non-AG database… Read more
In the previous blog http://blogs.msdn.com/b/sqlserverstorageengine/archive/2011/12/22/alwayson-challenges-with-statistics-on-readonly-database-database-snapshot-and-secondary-replica.aspx we described that stale or missing statistics will potentially lead to a sub-optimal query plan and how it can impact the query performance on on read-only database, database snapshot and readable secondary. This blog describes how we have solved this in SQL 12 for all three flavors of databases transparently… Read more
I am sure you all have dealt with situations when the statistics on one or more columns is either missing or not up-to date. When user submits a query for execution, the SQL Server goes through logical (simplifying or restructuring a query) and physical optimization that considers various query plans based on statistical information and… Read more
In my previous blog http://blogs.msdn.com/b/sqlserverstorageengine/archive/2011/12/22/alwayson-minimizing-blocking-of-redo-thread-when-running-reporting-workload-on-secondary-replica.aspx, I described how Readable Secondary eliminates potential REDO thread blocking for DML work running on the primary replica by mapping all isolation levels used in the reporting workloads to Snapshot Isolation. While it was essential that we eliminate REDO thread blocking with concurrent DML on secondary replica, it comes at… Read more
In earlier blog http://blogs.msdn.com/b/sqlserverstorageengine/archive/2011/12/22/alwayson-impact-on-the-primary-workload-when-you-run-reporting-workload-on-the-secondary-replica.aspx, I discussed the impact on RTO in case the REDO thread gets blocked. While designing this feature, it was one of the key usability constraints we had (i.e. to eliminate REDO blocking for common usage scenario). For the un-initiated, here is the problem Primary Replica Secondary Replica Set Isolation… Read more
The primary goal of AlwaysOn technology is to provide High Availability for Tier-1 workloads. The ability to leverage secondary replica(s) to offload reporting workloads and database/transaction log backups is useful, but only if it does not compromise High Availability. This is one of the very common concern/question that I have heard from many of you…. Read more
One question that I often get asked is if there will any data latency if you are using ‘Sync’ replica for read workload. The short answer is yes. Here is the blog that explains it in detail. While the reporting workload running on the secondary replica gets to access the data as it is changing… Read more
In the previous blog http://blogs.msdn.com/b/sqlserverstorageengine/archive/2011/12/22/AlwaysOn-setting-up-readable-seconary-replica.aspx I mentioned that there are two options to configure secondary replica for running read workload. The first option ‘Read-intent-only’ is used to provide a directive to AlwaysOn secondary replica to accept connections that have the property ApplicationIntent=ReadOnly set. The word ‘intent’ is important here as SQL Server makes no application check to guarantee… Read more
The easiest way to create an availability group and adding replicas is to use the availability group wizard. You can invoke the wizard by right-clicking on ‘Availability Groups’. The picture of the explorer window below shows that I have created 1 availability group ‘StockPro’ with two replicas ‘SUNILA03-6PLHSI’ (primary) and ‘SUNILA03-YLZO1U’ (secondary). The availability group StockPro contains one… Read more
This series of blogs is targeting AlwaysON Readable Secondary. Please refer to http://blogs.msdn.com/b/sqlalwayson/archive/tags/availability+group/for other blogs in the related area Readable Secondary is part of AlwaysOn suite of functionality available in SQL12 release. It allows customers to leverage their investment in High Availability hardware for offloading read workload such as reporting to one or more secondary… Read more