Hello i have SQL with few left joins and cases. Time on postgres is around one second and on oracle is 20minuts! (390 row postgres, 300 rows oracle). Configuration of tables are the same in both db. If i run in oracle EXPLAIN PLAN FOR for this sql first, then when i run SQL (without EPF) it is fast as on postgres. I can even make some changes, add colums etc and it still run nice and fast.
Is here someone who understand what is this and what solution i can use in java where query is used?
Related
Is there a way to identify the number of sql running parallel in Oracle 10g database?
What would be the maximum number of SQL run in Oracle at a time?
This is really needed to identify the performance of database response time. There is a use case wherein nearly 1 million sql need to be fired and amount of data in the table also few billions.
Really much appreciated your help in this.
Some programm generate and send queries to sql server(on high load production). I want take plan of concrete query of concrete table. I start profiler with "Showplan XML" and set filter on TextData(like %MyTable%) and DatabaseName. It show rows with xml in TextData that describe execution plans(for all queries of my table). But I know that exist 5 different sql queries for this table.
How I can match some concrete query with correspond plan without use statistic?
Is there a reason this has to be done on the production environment? Most really bad execution plans (missing indexes causing table scans etc.) will be obvious enough on a dev environment where you can use all the diagnostics you want.
Otherwise running the SQL on the query cache (as in the linked question someone else mentioned) will probably have the lowest impact as it just queries a system table rather than adding diagnostics to every query.
Let‘s say we have got a large number of SQL queries which take a long time to run. Now, we would like to make some changes to the database and re-execute the queries. We could rerun everything, but I would prefer a solution where only those queries are executed which are affected by the changes.
Do you know of any method to obtain the relevant tables/columns for each query? A simple example would be:
(let's consider this table: TABLE1 with columns: A;B;C)
SELECT C FROM TABLE1 WHERE B>10;
I would like to know that TABLE1.B is participating in this query.
Edit: the database is HSQLDB and is used from Java via JDBC.
Are you using any workbenck to execute your sql queries ? In Mysql workbench you have query optimizer option under which you can check which query has excuter and what actions has performed with the query result in a tree block diagram which certainly helps you here and you can also parse your query and check your resuls in query optimizer :) Hope it helps to you.
I have inherited an existing system and am trying to figure out a few things.
The system does a
SELECT * FROM v_myView WHERE mvViewCol = 'someValue'
and v_myView performs summation of Table1 based on myViewCol
Does SQL Server 2005 optimize the query or will summation always occur across the entire Table1?
I understand that I could use a parameterized view but don't want to go changing things unnecessarily.
Cheers
Geoff
Views have no runtime cost at all. They are always inlined into the surrounding query as if you had pasted the view definition as text. They would be impractical to use otherwise.
Does SQL Server (2005) optimize the query or will summation always occur across the entire Table1.
It will be optimized.
This is a complicated question. I think the best explanation is here. I do wish Microsoft documentation were a little clearer on this point.
When a view is created, the query is parsed. This ensures that it is correct.
The execution plan is determined the first time the query is run (to a close approximation). This execution plan then remains in the plan cache for subsequent calls. So, if you have an index on the appropriate columns and the first execution has a where clause that would use the index, then subsequent calls will also use the index.
I say to a close approximation, because it is really the first time that a view is called when the plan is not in the plan cache. Certain changes to the database will flush the plan, as will restarting the server.
So, if you only access the view with the where clause, then subsequent uses of the view will be optimized for that purpose.
SQL Server 2005 will optimize the view each time it is referenced in a query : http://technet.microsoft.com/en-us/library/cc917715.aspx
"After view expansion, the SQL Server query optimizer compiles a single execution plan for the executing query."
I don't have 2005 installed but it will operate similiar to 2008R2 - To view the Query Optimization Plan, right click in the query window and select "Display Estimated Execution Plan" for more info and to spot any bottlenecks.
In the Query menu option, there is "Analyse Query in Database Tuning Advisor" that may also be of benefit to you.
I would like to know if there is any tool which will give me the optimized SQL query for which ever query I specify. So that I can improve my DB as well as query performance. I use SQL Server 2008.
Thanks in advance.
The old Rule of DBs still applies, don't try to optimize sql statements, since the DB query parser will do its own optimizations anyway, instead do right away what we all do in the end:
Create indexes to increase performance
Don't get me wrong of course sql queries can be written stupidly and will therefore perform badly, but as long as you created a sensable 'normal' query, the query optimizer will do the rest together with the indexes.
SQL Server will even tell you if a query will clearly benefit from an index when you look at the execution plan. It will even generate the DDL statement to create the index, so all you have to do is copy/paste and run it to have the index your query needs.
You can already watch the execution plan that gives you SQL Server Management Studio.
You can try Redgate, they have evaluation versions for most of their products:
Redgate Website
SQL Server 2005 and up comes with a Query Optimizer. This can help, but tools can't really do too much optimization suggesting for you because they don't know what you are trying to accomplish.
You might try taking a look instead at some ways in which you can optimize your queries. Here are some links to get you started.
Tips, Tricks, and Advice from the MS SQL Query Optimization Team
SQL Server Rules for Optimizing Queries, best practices
Statistics Used by the Query Optimizer in SQL Server 2008
SQL Server 7.0 / 2000 came with 'index tuning wizard' this functionality has been around for a long time.
I'd reccomend having a look at 'select * from sys.dm_db_missing_index_details'
It tells you which indexes are 'missing', it's trivial to look in that table and then create indexes