I'm studying of Azure Synapse.
In dedicated SQL pool database, 'actual execution plan' of SSMS was disabled.
In serverless pool database, SSMS says 'set statistics is not supported.' in SQL execution.
I forgot of take screenshot. Image of 'disable of actual execution plan' is '4. Run the query by selecting Execute or use the following shortcut: F5.' of this page.
I understood SSMS could only shows plan of SQL, and not shows actual plan and live statistics.
But I still mysterious thing is how Synapse experts make faster SQL in Synapse?
In synapse, they don't use complex SQL(ex. much of outer join SQL)?
If my question is completely misunderstood of Azure Synapse system, please point out me.
Later versions of SQL Server Management Studio (SSMS), v18.x plus do support estimated execution plans for Azure Synapse Analytics dedicated SQL pools so the first thing you should do is check your version and update to the latest one. Here is an example plan from SSMS against a dedicated SQL pool, you can see it's got a Round Robin operator:
In terms of performance, you should generally look to hash partition your large fact tables on a key that gives good distribution and replicate your small dimensions. Use round robin distribution as a starting point or where you find it's appropriate for performance with your workloads. Use EXPLAIN to view text-based estimated execution plans. Visual Actual Execution Plans are not supported for but you can review the performance DMVs like sys.dm_pdw_request_steps:
SELECT *
FROM sys.dm_pdw_request_steps
WHERE request_id = 'QID####'
ORDER BY step_index;
Further details on this listed here.
Related
I am having trouble finding documentation regarding column statistics on a Microsoft Azure SQL Server database. I noticed recently that query plans had warnings in SSMS due to missing column statistics. Further investigation revealed that 'Auto Create Statistics' and 'Auto Update Statistics' were turned off for our database.
I understand that with our local SQL databases statistics are important to performance in that they let the query analyzer make educated guesses about the cardinality of results. Are statistics still important in an Azure SQL database? Is there any documentation about best practices here? Are there cases where automatic statistics should be turned off?
There is no difference between statistics in SQL Server and Azure SQL Database. Azure SQL Database is just a manged, and automatically-updated flavor of SQL Server. Here's the doc page: Statistics
Are there cases where automatic statistics should be turned off?
Rare cases. The vast majority of SQL Server databases rely on automatic creation and updates of statistic, perhaps augmented by scheduled index maintence.
Automatic statistics are created when needed, and will be created before the query that needs them can be optimized. Sometimes this can cause an unacceptable delay, so you would set them to create asynchronously, and let the query proceed without them, or rely on a manual process review and create needed indexes and statistics.
I need to measure the SQL Azure DB performance using DTA, is it possible or not, if not what is the workaround to consume a workload file (.trc)??
Database Engine Tuning Advisor does not support Azure SQL Database. It is also not possible to create a trace file from an Azure SQL Database using SQL Server Profiler.
SQL Azure automates the creation of indexes that may improve performance of your workload with a feature named automatic tuning. Automatic Tuning on Azure SQL also drops redundant indexes and uses the best execution plan for queries
Alberto is correct - there are features within SQL Azure which help watch and improve the performance of your database queries automatically in some cases. Profiler trace + DTA are not currently supported in SQL Azure. The DTA (Database Tuning Advisor) feature in SQL Server is very good for taking traces and trying to replay them on a different server to simulate possible index and partitioning changes which could improve your performance. The automatic tuning feature does that for you without having to use DTA today yourself.
https://learn.microsoft.com/en-us/azure/sql-database/sql-database-automatic-tuning
If all you want to do is explore the performance of your database, then you can use the query store in SQL Azure (and SQL Server 2016+) to do this kind of analysis.
https://azure.microsoft.com/en-us/blog/query-store-a-flight-data-recorder-for-your-database/
https://learn.microsoft.com/en-us/sql/relational-databases/performance/monitoring-performance-by-using-the-query-store?view=sql-server-2017
If you have not tried this using a recent release of SQL Server Management Studio(SSMS), then I highly suggest you download this and try it. You can see top N queries by different metrics, plan changes over time, and other metrics which give you faster insight into the performance profile of your database + application.
There is no way to take a .trc file today and examine it in the query store, but you can enable query store in an on-premises SQL Server (2016+) and then record your production workload for awhile to see how it is behaving. Please understand there is an overhead to running with the query store on - usually it is modest, but for highly ad hoc OLTP query workloads you may see larger overhead. There are some knobs to tune this, so please just go through normal due diligence before modifying a production system. If you have problems, turn it back off and re-examine until you have the right settings to help capture the relevant data from your workload to help make tuning decisions.
Hope that helps!
Sincerely,
Conor Cunningham
Architect, SQL
SQL Server Enterprise Edition's query optimizer will use indices from a view to increase performance of a query even if the view is not explicitly referenced in the query, if applicable. Question: does Azure Database do the same thing? I know SQL Server Express does not do this, for example. I want to ensure I can still get the performance I need from the query optimizer when doing a sort on a joined table with a few million users (works great on enterprise edition but takes several seconds on express - bottle neck at the sort).
Sometime last year (2012) Microsoft announced that the engine was the same between SQL Server and SQL Azure (now called Windows Azure SQL Database :/). So you will likely get the same behavior. Same performance may be another question. Windows Azure SQL Database is also keeping replicas in place in the event of hardware failure. You get the benefit of the secondary coming online in a fashion that is seamless to you. But, This does have a bit of a performance cost. Also, the SQL running in Windows Azure is running in a shared environment. It is pretty well documented that the performance is not the same as a local dedicated multi-processor machine with fast storage. It is a bit of an unfair comparison multi-user, multi-instance vs. dedicated. For many applications this is fast enough, but not all.
I am looking for information about how SQL Server actually handles query execution in finer details (like what data is kept in buffer/memory and how does it decide to get fresh data even if there is an update change in only one column of a table involved in a query etc)
If anyone knows sources please let me know?
We have an web application using sql server 2000, it has heavy frequent reads almost 70% of the tables(dashboard) every 30 seconds. and at the same time lot of writes are happening.
Please let me know any tips for optimization of above scenario?
No one is going to be able to give you an answer on how to solve your optimization problem. This requires access to your database server. To solve your problems you need to understand roughly how the database works, and for this you need to do some reading.
On-line resources are OK, however the following three books are priceless. The first two books have very detailed information about how SQL Server works. The last ones is a guide of how to write queries but with a discussion on how the engine views queries as well.
Kalen Daleney: Sql Server 2008 Internals
Sql Server 2005: Practical Troubleshooting:
Ben Gan et al: Inside SQL Server 2008: T-SQL Querying
It would take a lot of posts to answer the internal's type questions, I suggest you start reading some of the white papers / blogs and some books.
For 2000 Ken Henderson's SQL Server Architecture will give you deep internal details, for the more recent editions of SQL, he did a 2005 practical trouble shooting which isn't bad, and Kalen Delaney's SQL 2008 Internals book is very good.
You should examine the execution plan.
Press Ctrl-L in the SSMS or issue SET SHOWPLAN_TEXT ON before executing the query.
This will give you detailed information of what indexes are used, which join algorithms applied etc.
You may also want to see the statistics:
SET STATISTICS TIME ON
SET STATISTICS IO ON
, which will give you the information on how many reads were done from actual tables, cache etc., and how much time (actual and CPU time) did every query take.
About SQL Server 2008 buffer management: http://msdn.microsoft.com/en-ca/library/aa337525.aspx
Then you can browse with the left sidebar for information on other subjects.
As far as external sources go, MSDN has a comprehensive resource on optimising your SQL Server 2000 installation, particularly the Patterns & Practices paper on performance and scalability.
If you know where to start looking, take a bottom-up approach with examining SQL profiles and query plans as has been mentioned. Otherwise, start from the top down and learn about the costs involved in recompiling queries, how to index effectively, and how the query optimiser uses statistics.
in my previous workplace we used oracle enterprise manager for viewing statistics and bottlenecks of queries that are running against oracle10g. In my new workplace we use Microsoft SQL Server (2005). Is there any tool like enterprise manager of oracle in SQL Server - I need to see all the jdbc SQL queries i make and how long they are taking in the db..
thanks
Use SQL Server Profiler for tracing DB queries and such.
If you are looking for costs of queries and how they break down, you should use the Query Analyzer that is built into SSMS.
For SQL 2005 SP2 and later, you can download the Performance Dashboard Reports from MS (free).
Quote:
Common performance problems that the
dashboard reports may help to resolve
include:
- CPU bottlenecks (and what queries are consuming the most CPU)
- IO bottlenecks (and what queries are performing the most IO).
- Index recommendations generated by the query optimizer (missing indexes)
- Blocking
- Latch contention
The information shown in the reports is from the dynamic management views which you could query yourself if you didn't want to download this addon.
A combination of 'SQL Server Profiler', 'SQL Server Management Studio' and 'Database Engine Tuning Advisor' will be your friend. Have a look at showing the estimated and actual execution plans using SSMS, or create trace files with SQL Server Profiler (using the Tuning template) to feed to the Database Engine Tuning Advisor
I'm using Qure Analyser (free) which I've found very useful. It works by analysing a SQL Server trace file (.trc) and showing you which queries take up most CPU time, cause the most IO, or are called most often. Useful for spotting problems in the application code which may cause it to abuse the database.