Is it true that one query is one transaction in Azure SQL DTU? that mean is my basic package has 5 DTU it won't execute more than 5 quires in one second?
I am wondering how much DTU it will take to execute a query where sub query runs 1,000 times.
DTU, abbreviation for Database Throughput Unit, is involved with multiple factors including CPU, Memory, reads and writes. Not just queries per seconds or transactions at a time.
There is a calculator for you to measure your on-premise database, if you want to migrate it to Azure SQL database.
And, there is an test for Azure SQL Database Benchmark with different Service Tier/Performance Level
No, this is not the amount of queries per second.
It is rather a bit of a blackbox calculation based on:
Processor
% Processor Time
Logical Disk - Disk Reads/sec
Logical Disk - Disk Writes/sec
Database - Log Bytes Flushed/sec
there is however a calculator that helps you defining the correct amount of dtu's you consume on: http://dtucalculator.azurewebsites.net/
As other have already indicated, the DTU does not reflect queries per second. I recommend you enable SQL Azure Query Performance Insight which will allow you to track DTU usage and identify the top DTU consuming queries.
Also, there is no such concept as a 'sub-query' in execution. There is only the 'query'. If your query contains 'sub-queries' they are nothing more than just parts of the 'query' and in the end there is one query being executed. Your query components (sub-queries, scalar or table valued functions, CTEs, 'lateral views' etc etc ) are all just parts of the one query, and there is one query being executed, no matter how many components it has and how often their operators get invoked. Some queries consume more DTUs than other, but the relation between query text complexity and query execution complexity/cost is not straightforward. Please read Understanding how SQL Server executes a query for a deeper discussion on this topic.
Related
I want to find those queries in MS Access which are utilizing the CPU mostly and put them in a table in descending order.
I have checked the system tables of MS Access database, but can't find any clue for this.
I am new to MS Access, please help.
For 10 or even 15 years, Access has never been CPU bound. In other words, network speeds, disk drive speeds etc. are the main factor .
In the vast majority of cases throwing more CPU at a problem will not help improve performance. If 99% of time is network or other factors, then a double of CPU will only improve by 2%.
However, I will accept that if a query is using lots of CPU, then it stands somewhat to reason that such a query is pulling a lot of data. There is no CPU logger for the Access database engine. However, you can look at rows and the query plan, and that can be done with showplan. How this works and can be used is outlined here:
How to get query plans (showplan.out) from Access 2010?
And here is a older article on showplan and how to use it:
https://www.techrepublic.com/article/use-microsoft-jets-showplan-to-write-more-efficient-queries/#
So, showplan is somewhat similar to looking at the query plan used in SQL server. It will tell you things like if a full table scan is being used to get one row, or if indexing can or was used. So, looking at the query plan, be it sql server, or in this case Access is certainly possible. However, the status on CPU usage are slim, but how much data and things like if the query plan is doing full table scans is available in a similar fashion to query plans like one would see for server based systems such as SQL server.
I have a not simple query.
When I had 10 DTUs for my database, it took about 17 seconds to execute the query.
I increased the level to 50 DTU - now the execution takes 3-4 seconds.
This ratio corresponds to the documentation - more DTU = work faster.
But!
1 On my PC I can execute the query in 1 sec.
2 In portal-statistics I see that I use only 12 DTU (max DTU percentage = 25% ).
In sys.dm_db_resource_stats I see that MAX(avg_cpu_percent) is about 25% and the other params are less.
So the question is - Why my query takes 3-4 sec to exec?
It can be executed in 1 sec. And server does not use all my DTU.
How to make server use all available resources to exec queries faster?
DTU is a combined measurement of CPU, memory, data I/O and transaction log I/O.
This means that reaching a DTU bottleneck can mean any of those.
This question may help you to measure the different aspects: Azure SQL Database "DTU percentage" metric
And here's more info on DTU: https://learn.microsoft.com/en-us/azure/sql-database/sql-database-what-is-a-dtu
On my PC I can execute the query in 1 sec
We should not be comparing our Onprem computing power with DTU.
DTU is a combination of CPU,IO,Memory you will be getting based on your performance tier.so the comparison is not valid.
How to make server use all available resources to exec queries faster?
This is simply not possible,since when sql runs a query,memory is the only constraint ,that can prevent the query from even starting.Rest of the resources like CPU,IO speed can increase or decrease based on what query does
In summary,you will have to ensure ,queries are not constrained due to resource crunch,they can use up all resources if they need and can release them when not needed.
You also will have to look at wait types and further fine tune the query.
As Bernard Vander Beken mentioned:
DTU is a combined measurement of CPU, memory, data I/O and transaction
log I/O.
I'll also add that Microsoft does not share the formula used to calculate DTUs. You mentioned that you are not seeing DTUs peg at 100% during query execution. But since we do not know the formula, you may very well be pegging components of DTU, but not pegging DTU itself.
Azure SQL is a shared environment, and each tenant will be throttled to ensure that the minimum SLA for all tenants
What a DTU is is quite fuzzy.
We have done an experiment where we run a set of benchmarks on machines with the same amount of DTU on different data centers.
http://dbwatch.com/azure-database-performance-measured
It turns out that the actual performance varies by a factor of 5.
We have also seen instances where the performance of a repeated query on the same database varies drastically.
We provide our database performance benchmarks for free if you would like to compare the instance you run on your PC with the instance in the azure cloud.
I have a sql server running on my machine.It contains 10 data base file.
say
a
b
....
z
so my question is 10 or more database or 1 single database is best for sql server .Does more database cause more performance issue on single server machine? what is recommended?
You may think like:
"Using multiple databases helps like they are outer index and it can be helpfull for search times.
Think like that, when searching begins, your database server takes your query it will go the firstly to your table and it will execute query on that table and which helps for querying time because datas on other tables will not be looked only your table index will be looked at tables table. :)
In same manner when you group your tables on different dbs query will begin to look just table index of that table on tables table and because there will be less table in that table finding your tables table id will going to complete in less time. :) "
But that is not correct! If you dont have millions of tables it will not going to impact because datastructures used on dbs mostly acces data in O(log(n)) and that means that if(Big if) accesing in 1,000,000 input takes 6 step complete then 100,000 will take 5 step and 1,000 will take 3. As you can see it not makes difference.
On the other hand using 2 db guarantees that it has to be at least 2 connections and connections are expensive things and that is why connection pools are exist.
Mostly Common issue is for poor database design
The causes for performance problems can be various, but the most common are a poorly designed database, incorrectly configured system, insufficient disk space or other system resources, excessive query compilation and recompilation, bad execution plans due to missing or outdated statistics, and queries or stored procedures that have long execution times due to improper design
Memory bottlenecks are caused by limitations in available memory and memory pressure caused by SQL Server, system, or other application activity. Poor indexing requires table scans which in case of large tables means that a large number of rows is read from disk and handled in memory
Network bottlenecks are caused by overload on a server or network, so the data cannot flow as expected
I/O issues can be caused by slow hardware used, bad storage solution design, and configuration. Besides hardware components, such as disk types, disk array type, and RAID configuration that affect I/O performance, unnecessary requests made by a database also affect I/O traffic. Frequent index scans, inefficient queries, and out of date statistics can also cause I/O workload and bottlenecks
- See more at: http://www.sqlshack.com/dba-guide-sql-server-performance-troubleshooting-part-1-problems-performance-metrics/#sthash.QrzEyKbz.dpuf
Multiple Database is not a problem for performance.
you can see these links. I think it will help you about understanding performance tuning :D
I am new to database. I try to run a simple query on SQL Server 2014 and Oracle 12c.
This is the execution plan I get using SQL Server. It contains information about I/O cost and CPU cost in seconds.
However I can't find the same information using Oracle. The CPU cost shown in the execution plan is not based on execution time.
I want to do some comparison between the two databases. How I can obtain the same information in Oracle as in SQL Server? Besides, how I can know the cache hit ratio?
Thank you.
The cost estimate is in fact based on time.
It is a non-dimensionalised measurement that expresses the estimated time for the query to complete in terms of the equivalent number of logical reads, so if a logical read is expected to take 0.001 seconds then a cost of 12 is 0.012 seconds.
Although it is commonly stated that the cost between different queries cannot be compared, this was only definitively true in earlier versions. The difficulty in comparing query costs relates to how long single block and multiblock reads, writes and CPU operations take. This can depend on such a multitude of factors (other activity on the system, and activity immediately prior that affects the likelihood of blocks being cached by the instance or the i/o subsystem) that it is highly unlikely that you really expect to derive a time from a cost.
Cache hit ratios have been discredited for quite some time as a measurement of system efficiency. It is possible to improve the cache hit ratio to an arbitrary number by simply running particular types of highly inefficient queries.
Use the Oracle Database 12c: EM Express Performance Hub to get both estimates and actual values for queries and their operations. Regular explain plans are helpful, but they just show you what Oracle thinks will happen, not necessarily what will happen.
Specifically, use either the SQL Details (aggregate) or the SQL Monitor Details (last execution) information.
You're close, very close.
Run with AutoTrace.
I talk more about the feature here, or you can of course read up on the docs or the Help.
I want to tune a production SQL server. After making adjustments (such as changing the degree of parallelism) I want to know if it helped or hurt query execution times.
This seems like an obvious performance counter, but for the last half hour I've been searching Google and the counter list in perfmon, and I have not been able to find a performance counter for SQL server to give me the average execution time for all queries hitting a server. The SQL Server equivalent of the ASP.NET Request Execution Time.
Does one exist that I'm missing? Is there another effective way of monitoring the average query times for a server?
I don't believe there is a PerfMon but there is a report within SQL Server Management Studio:
Right click on the database, select Reports > Standard Reports > Object Execution Statistics. This will give you several very good statistics about what's running within the database, how long it's taking, how much memory/io processing it takes, etc.
You can also run this on the server level across all databases.
You can use Query Analyzer (which is one of the tools with SQL Server) and see how they are executed internally so you can optimize indexing etc. That wouldn't tell you about the average, or round-trip back to the client. To do that you'd have to log it on the client and analyze the data yourself.
I managed to do it by saving the Trace to SQL. When the trace is open
File > Save As > Trace Table
Select the SQL, and once its imported run
select avg(duration) from dbo.[YourTableImportName]
You can very easily perform other stats, max, min, counts etc... Much better way of interrogating the trace result
An other solution is to run multiple time the query and get the average query time:
DO $proc$
DECLARE
StartTime timestamptz;
EndTime timestamptz;
Delta double precision;
BEGIN
StartTime := clock_timestamp();
FOR i IN 1..100 LOOP
PERFORM * FROM table_name;
END LOOP;
EndTime := clock_timestamp();
Delta := 1000 * (extract(epoch FROM EndTime) - extract(epoch FROM StartTime)) / 100;
RAISE NOTICE 'Average duration in ms = %', Delta;
END;
$proc$;
Here it run 100 time the query:
PERFORM * FROM table_name;
Just replace SELECT by PERFORM
Average over what time and for which queries? You need to further define what you mean by "average" or it has no meaning, which is probably why it's not a simple performance counter.
You could capture this information by running a trace, capturing that to a table, and then you could slice and dice the execution times in one of many ways.
It doesn't give exactly what you need, but I'd highly recommend trying the SQL Server 2005 Performance Dashboard Reports, which can be downloaded here. It includes a report of the top 20 queries and their average execution time and a lot of other useful ones as well (top queries by IO, wait stats etc). If you do install it be sure to take note of where it installs and follow the instructions in the Additional Info section.
The profiler will give you statistics on query execution times and activities on the server. Overall query times may or may not mean very much without tying them to specific jobs and query plans.
Other indicators of performance bottlenecks are resource contention counters (general statistics, latches, locks). You can see these through performance counters. Also looking for large number of table-scan or other operations that do not make use of indexes can give you an indication that indexing may be necessary.
On a loaded server increasing parallelism is unlikely to materially affect performance as there are already many queries active at any given time. Where parallelism gets you a win is on large infrequently run batch jobs such as ETL processes. If you need to reduce the run-time of such a process then parallelism might be a good place to look. On a busy server doing a transactional workload with many users the system resources will be busy from the workload so parallelism is unlikely to be a big win.
You can use Activity Monitor. It's built into SSMS. It will give you real-time tracking of all current expensive queries on the server.
To open Activity Monitor:
In Sql Server Management Studio (SSMS), Right click on the server and select Activity Monitor.
Open Recent Expensive Queries to see CPU Usage, Average Query Time, etc.
Hope that helps.
There are counters in 'SQL Server:Batch Resp Statistics' group, which are able to track SQL Batch Response times. Counters are divided based on response time intervals, for example, from 0 ms to 1 ms, ..., from 10 ms to 20 ms, ..., from 1000 ms to 2000 ms and so on, So proper counters can be selected for the desired time interval.
Hope it helps.