How Are Simultaneous Queries Handled?
Oct 22, 2007
Hi,
I have an application resource that is accessible from multiple clients applications that all have access to a common SQL Server db. By this, I mean, multiple clients can potentially connect to this resource at any given time. I want to limit the usage of this resource to one client at a time and was thinking about simply using SQL to maintain the name of the client that currently has "control" of the resource.
My question pertains to the case where two clients are executing a SQL query, simultaneously, to check whether someone has control of the resource or not. If two users were to simultaneously execute this query, do i have to lock the table in order to ensure that both users are not viewing data in an incorrect state? Or, does SQL Server ultimately execute the queries in a specific order? Meaning, the requests are simultaneous from a human standpoint but one request may have actually come in a millisecond before the other one and SQL server executes that query first, and then the second query. Is this how it works?
Thanks,
Paul
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Dec 1, 2005
Hello everyone, I am hoping someone can help me with this problem. Iwill say up front that I am not a SQL Server DBA, I am a developer. Ihave an application that sends about 25 simultaneous queries to a SQLServer 2000 Standard Edition SP4 running on Windows 2000 Server with2.5 GB of memory. About 11 of these queries are over views (all overthe same table) and these queries are all done from JDBC but I am notsure that matters. Anyway, initially I had no problem with thesequeries on the tables and the views with about 4 years of information(I don't know how many rows off hand). Then we changed the tables toreplicated tables from another server and that increased the amount ofdata to 15 years worth and also required a simple inner join on 2columns to another table for those views.Now here is the issue. After times of inactivity or other times duringthe day with enough time between my test query run I get what lookslike blocking behavior on the queries to the views (remember these allgo to the same tables). I run my 25 queries and the 11 view queriesall take about 120 seconds each to return (they all are withinmilliseconds of each other like they all sat there and then werereleased for processing at the same time). The rest of the queries arefine. Now if I turn around and immediately run the 25 queries again,they all come back in a few seconds which is the normal amount of time.Also, if I run a query on one of views first (just one) and then runthe 25 queries they all come back in a few seconds as well.This tells me that some caching must be involved since the times are sodifferent between identical queries but I would expect that one of thequeries would cache and thus take longer but the other 10 would befast, not all block for 2 minutes. What is more puzzling is that thisbehavior didn't occur before where now the only differences are:1) 3 times more data (but that shouldn't cause a difference from 3seconds to 120 and all tables have been through the index wizard with aSQL trace file to recommend indexes)2) There is now a join between 2 tables where there wasn't before3) The tables are replicated throughout the day.I would appreciate any insight into this problem as 120 seconds is waytoo long to wait. Thanks in Advance.Chris
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Mar 13, 2008
How can we continue with the rest of the iterations in ForEach Loop after handle an error.
I Have a dataflow task inside a for-each loop and processing a set of flat files in that. When error occurs in the dataflow task, i moved that particular flat file to another location. But, If an error occurs at first falt file, It moves that flat file to the location i specified and not continue with the next file (The Execution finished at that stage itself afetr the first flat file).
I Set the FailParentonFailue of Dataflow task to TRUE (Since its inside the for loop).
Any thing i have to change ? Or Where i miss the thing.
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Jul 20, 2005
Hi,I would like to know if anyone out there really uses SQLServer 2000 (which edition?) to hold the data for a datawarehouse? How much data does it handle efficiently?TIAFrank
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May 2, 2006
If multiple snapshots for the same report attempt to generate at the same second, is there something in place to prevent them from conflicting with each other?
Our SSRS 2005 application will use a console app that we are writing to change the default parameters on each report and call the CreateReportHistorySnapshot method. This application will be multi-threaded, so there is a possibility that multiple versions of the same report with different parameters will attempt to run at the same time. We need to be sure that these snapshots will not conflict and return the appropriate SnapshotHistoryID for that report run.
From looking at the History table in the ReportServer database it looks like there are uniqueIDs and other keys that would prevent duplicates, but what if the requests come in at the same time? Is SSRS 2005 smart enough to delay for a second so that there is not a duplicate? Since the way you reference these snapshots in your URL is with the Snapshot Time in UTC format, that only goes out to full seconds (2006-05-02T00:00:00).
Sorry for the length, but I could not think of how to condense this.
Thanks,
Steve
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Mar 12, 2006
I have C# Express and the SQL Express Management Studio CTP installed. So far, I've been forced to disconnect from the server in one app to connect to it in the other. I understand there is something around a 4 connection limit in SQLServer Express, so I don't see the problem.
During one of these episodes, SQL Mgmt Studio hung while opening DB properties, then the SQLServer service couldn't be stopped. Now the DB can't be opened even after a reboot.
Help?
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Mar 29, 2000
How can I simulate 1,000 simultaneous users in my database?
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Mar 22, 1999
Is there a limit to the # of tasks ( Dumps) to a HD device ,which SQL 6.5 can perform simultaneously?
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Feb 14, 2008
Hi All,
I have a Windows 2003 Server. Planning to use SQL Server to act as the main Database Server which needs to cater to over 100's of simultaneous connections.
Can anyone share with me the default maximum simultaneous connections and the maximum allowed simultaneous connections for the following versions:
- MSDE
- 2000
- 2005 Express
- 2005
Hope I can get more professional advice from you guys.
Thanks.
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Jul 11, 2006
Using the Import/Export Wizard, it is easy to set up SSIS jobs to import multiple tables in one task. However, SSIS appears to grab a connection to the source database and the destination database for each table indicated in the task sometime prior to doing the actual data transfer. Even though the transfer seems to be done a few tables at a time, all the connections are held throughout the execution of the task.
This has two effects:
1. The task may fail if the number of connections exceeds the limit of user connections set for the database
2. There is a severe impact on the other users of the databases (in my case, the source is a production system)
Is there any way to control the number of simultaneous connections that SSIS data transfer packages initiate?
I can, of course, define the package to have a small number of tables (thus limiting the connections), but in real life I need to transfer almost 700 tables, so limiting the number of tables per task to 20 or 25 produces an awkwardly large, and error prone, number of tasks. And since this definition must be done for multiple (not quite identical) databases, the extra effort of defining small collections of tables is signifcant.
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Aug 14, 2007
Greetings!
Are there any limit of simultaneous users and/or connections when running SQL Express? The free license of SQL Express, does that include use by any number of users/devices?
Regards
Harald Hedlund
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Apr 7, 2008
Hi, can anyone help me? I want to know whether is it possible to insert records simultaneously in both master & detail tables?
For elaboration, say there is a master table contains (orderid,orderdate,amount) and details table contains (orderid, productid,qty,price). 1 record of master table associated with n records of details table. Can it be possible to insert both the 1 record at master table with n records in details table in a single sql statement?
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Jul 20, 2005
hello to all,there are two databases named A and B.One database contains employee id as primaryI have another project database which includes that employee id asforeign key. How can I reflect my updations,deletionsthank you in advance,vishnu
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Oct 15, 2007
Is there a way to get the Report Manager to allow a single user to
execute more than 1 report at a time? Currently, each user can only
have a single report being executed at a time. It looks like any
other reports are being queued and executed serially.
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Oct 23, 2007
How can I prevent a package, or a section of a package, from being run more than once simultaneously? The package makes use of a staging database table, and if two copies of this package are run at the same time, there will be a race condition and possible corruption of the data in the database table. I have also noticed that the SSIS logging gets messed up and starts overwriting itself if I have more than one of these packages run at the same time.
What I am thinking of should work the same way as a serializable transaction lock on a normal query, where one query has to wait if another query has a lock on the table. I don't want the package to throw an error, I want it to wait until the other one is done.
I have been trying to use transactions in a test SSIS package, but they are not quite doing what I want them to do. I put various SSIS steps in a sequence container and require a serializable transaction. I have also tried putting the transaction at the package level, but that is not preventing simultaneous package runs.
Is there a built-in way to do this that is easy to implement? Otherwise, what I could do is insert a flag into the database indicating that a package is running, then make sure to reset the flag on any error or on completion. It seems like this alternate method could be error-prone though.
I am using SP2.
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Feb 8, 2007
I am trying to insert into two tables simultaneously from a formview. I read a few posts regarding this, and that is how I've gotten this far. But VWD 2005 won't let me save the following stored procedure. The error I get says “Incorrect syntax near ‘@WIP’. Must declare the scalar variable “@ECReason� and “@WIP�.� I'm probably doing something stupid, but hopefully someone else will be able to save me the days of frustration in finding it. Thanks, the tables and procedures are below.
I made up the two tables just for testing, they are:
tbltest
ECID – int (PK)
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Mar 30, 2001
Hi,
could somebody please let me know what is the maximum number of simultaneous users/connection per single SQL Server 7.0 box? Licenses are not the issue here, rather the number of physical connections supported before another server needs to be purchased.
Another variation of this question would be what's the highest number of databases that 7can be created on SQL 7.0 server and what is the highest number of physical connections supported per database? Again, licenses are not the issue. Thanks a lot in advance.
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Sep 28, 2007
I was going over this article , and was intrigued by this statement "If SQL Server 2005 Express is running on Windows XP Home, it is limited to five simultaneous connections. If it is running on Windows 2000 or Windows XP Professional, it is limited to 10 simultaneous connections. However, these are limitations of the operating system and not of SQL Server 2005 Express."
What are simultaneous connections? Is this related to Max worker threads defined as 255 on other editions? How does underlying OS impose how many connections can be done to SQL server. And finally how many simultaneous connections can be done in Windows Server 2003?
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Jul 26, 2007
Hello
I am trying to call the same package with different starting parameters using asynchronous method calls.
My code is
namespace ReconHost
{
public partial class HostContainer : Form
{
public delegate void InvokePackageHandler(
Microsoft.SqlServer.Dts.Runtime.Application app,
int var
);
Microsoft.SqlServer.Dts.Runtime.Application app;
public HostContainer()
{
InitializeComponent();
for (int i = 0; i < 2; i++)
{
app = new Microsoft.SqlServer.Dts.Runtime.Application();
InvokePackageHandler asyncInvokePackageHandler = InvokePackage;
asyncInvokePackageHandler.BeginInvoke(app, i, null, null);
}
}
public void InvokePackage(Microsoft.SqlServer.Dts.Runtime.Application app, int var)
{
Package pkg = app.LoadPackage(@"c:GRSGRSGRSTest_Async.dtsx", null);
pkg.Variables["intVar"].Value = var;
pkg.Execute();
pkg = null;
}
}
}
If I set the for loop to loop just once, the package is executed fine. Any more than once and only one instance of the package is executed.
Does anyone know what I am doing wrong? I know it is possible to execute the two package instances simultaneously because you can use DTexecUI.exe on two clients to do this.
Thanks in advance
Tomo
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Jul 30, 1998
Hi everyone!
Is it possible to control the number of simultaneous connections one login id can have?
I`d like to avoid my users to share their login ids and passwords to help them enter data into the system.
Thanks,
Mauricio
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Mar 30, 2007
Hi everyone. I hope that my question isn't too broad, but here it goes...
I am trying to figure out the best way to scale a SQL Server database so that it can handle a billion simultaneous users querying the same tables, and can easily scale to handle many billions of simultaneous users. The database must also have 999.99% availability. The number of licences and amount of hardware needed is not an issue.
Thanks in advance.
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Jul 27, 2006
Hi Everyone,
I have a software solution that consists of two separate applications that share a SQL Server Express database on a single computer. Everything is working great, except when both of the applications want to access the database at the same time. All I can find is information on configuring multi-user access in a distributed system. I'd appreciate any information on configuring multi-application access on a single computer.
Thanks,
Mike
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Mar 20, 2007
Hello, I have one store procedure that writes something data to one physical sql table 'MyTable' and on beginning I first call:DELETE FROM MyTableProcedure returns at the end data from 'MyTable' as on SELECT. PROBLEM:I started SQL Manager on my Laptop and on Computer near me and all pointed to same database (on Server) and I run that procedure simultaneously on Laptop and Computer at the same time (two hands on F5 button on these computers). Occasionally when clicking with both hands at the same time I got no records at the end of execution (on both computers), otherwise I got the results.WHAT I THINK IS PROBLEM:Somhow one SP start working and it did not come to the end and another computer called this SP and execute first command (DELETE FROM MyTable) and I got empty records at the end..WHAT I NEED:I need to prevent this situation to get empty records. All computers must get these records always. How I can use some sort of LOCKs to do this?Or to do that on C# application level using LOCK command? Thanks in advanceAleksandar
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Jul 20, 2005
HelloWhen I use a PreparedStatement (in jdbc) with the following query:SELECT store_groups_idFROM store_groupsWHERE store_groups_id IS NOT NULLAND type = ?ORDER BY group_nameIt takes a significantly longer time to run (the time it takes forexecuteQuery() to return ) than if I useSELECT store_groups_idFROM store_groupsWHERE store_groups_id IS NOT NULLAND type = 'M'ORDER BY group_nameAfter tracing the problem down, it appears that this is not preciselya java issue, but rather has to do with the underlying cost of runningparameterized queries.When I open up MS Enterprise Manager and type the same query in - italso takes far longer for the parameterized query to run when I usethe version of the query with bind (?) parameters.This only happens when the table in question is large - I am seeingthis behaviour for a table with > 1,000,000 records. It doesn't makesense to me why a parameterized query would run SLOWER than acompletely ad-hoc query when it is supposed to be more efficient.Furthermore, if one were to say that the reason for this behaviour isthat the query is first getting compliled and then the parameters aregetting sent over - thus resulting in a longer percieved executiontime - I would respond that if this were the case then A) it shouldn'tbe any different if it were run against a large or small table B) thisperformance hit should only be experienced the first time that thequery is run C) the performance hit should only be 2x the time for thenon-parameterized query takes to run - the difference in response timeis more like 4-10 times the time it takes for the non parameterizedversion to run!!!Is this a sql-server specific problem or something that would pertainto other databases as well? I there something about the coorect use ofbind parameters that I overall don't understand?If I can provide some hints in Java then this would be great..otherwise, do I need to turn/off certain settings on the databaseitself?If nothing else works, I will have to either find or write a wrapperaround the Statement object that acts like a prepared statement but inreality sends regular Statement objects to the JDBC driver. I wouldthen put some inteligence in the database layer for deciding whetherto use this special -hack- object or a regular prepared statementdepending on the expected overhead. (Obviously this logic would onlybe written in once place.. etc.. IoC.. ) HOWEVER, I would desperatelywant to avoid doing this.Please help :)
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Aug 9, 2006
Hi,
I am using visual web developer2005 express edition and finding hard time to get my query run in this i am making my own login page as i have few more things to ask to user before they get logged in so i am not using the login control.
i want to write my own query without help of sqlDataSource control from start something like
sqldatasource con=new sqldatasource;
con.connection String=""
then what all things will come........ ???
and please give me some poitners to some articles which help one to do the requested.
Regards,
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Dec 7, 2007
I have an update query which either inserts a row or increases quantity, depending if row exists or not. It works, better than my explanation probably.After that query could be a good time to count total of all calculated sub sums.Something like this. previous queryEND goSELECT SUM(SubTotal)FROM dbo.t_Shoppings I have tried this on the tool which has a long name, but I think my way didn't work. (Microsoft sql server management studio express)Is this possible or do I have make and call another stored procedure.I can send my sp if someone wants.
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Dec 18, 2007
how can i execute for example
2 queries together, in a single stored procedure Select top 20 * from Product where Active=1select Count( *) from product if i execute such one how can i get the 2 results in vb/c# ?
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Jun 18, 2004
hi which is bettere to use a quesry from the code or to use a Stored Procedure and call the SP from the code
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Oct 21, 2004
Hi All,
Not sure if I've got the correct place for this question. But, I'm trying to create and sql query to list the lates 10 items in a database. So far I haven't had any luck finding this.
All I have is a normal query (below). Can anyone help me please?
SELECT * FROM pages WHERE show = 'yes' ORDER BY id Desc;
Regards,
Rich
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Jan 23, 2006
Hi,I have 5 tables in sql database, naming Book, Category, Subject, UserDownload, User.In Book table, BookID, BookTitle, CategoryIDIn Category table, CategoryID, CategoryNameIn Subject table, SubjectID, SubjectName, CategoryIDIn UserDownload table, UserID, BookIDIn User table, UserID, UserNameI used Book to store information of books. Those books has many categories. In those categories, there is also some subjects.When user downloads book, I update UserDownload table.The result I want to get is, Top Ten Download Subject. How can I get? Please help me.
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Jul 16, 2002
Could anyone help me?I need all the commands like select,from etc.Basically I need to learn writing queries etc.Please
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Aug 3, 2000
I just upsized my Access2K db to SQL. I am using Front Page 2000 for my website. When I had the database as Access, I was able to use one of my Access queries as my record source for my data base. I was able to choose between my queries AND my tables as the source for my records. Now that I've upsized, I am no longer given that choice. My only choices are the tables. Unfortunately, my database is designed to pull records from a query, not just a table. So my question is, in FP2000, how do I use a QUERY from my newly upsized SQL db as my record source?
Thank you all very much in advance.
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Feb 7, 2003
Hi!
Where to write MDX Queries and how to call the query in Analysis Services.
Please help me on this.
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