I am working on a Windows desktop application built in VB.NET that interfaces with a web-based database (Microsoft SQL Server 2012). It connects to database when required and performs some calculations locally.
Now, there is a new requirement to execute a sproc from this Windows application. I need to know that when I call SqlCommand.ExecuteNonQuery, is the SqlCommand freed up immediately or it waits till the sproc has finished all work?
I cannot test right now because the stored procedure is yet to be designed and it is going to take minimum 2 min to complete.
I am running the SqlCommand.ExecuteNonQuery on a separate thread than the UI.
Concerns if SqlCommand is not freed up immediately:
1. If user exits the application before completion, will the sproc finish work?
2. If timeout occurs, will the sproc finish work?
Sorry if my doubts are basic in nature, I am a novice.
Yes, ExecuteNonQuery will wait until the SP is complete or errors.
If you are running the ExecuteNonQuery from another thread, only that thread is waiting. Other threads are not so the user can close the application. If you cleanup the thread before closing, as you should, it will send a cancel to the SP. (This does not mean it will actually cancel. If it is almost done, it may finish anyway.) What happens then is up to your SQL developer. If they run the SP inside a transaction, they should rollback the changes and return the error. If not, get a new SQL developer.
The method ExecuteNonQuery waits until the stored procedure finishes. The return will be an integer with the number of affected rows.
Related
I starting at a new company and am a web applications developer. So I am not a DB Guru, but have worked with it my entire career obviously being a developer. The company keeps randomly getting a locking issues, that then holds up the internal application an locks everyone. They then have to kill a service to correct the issue, and free up SQL. Now, I am wondering if when a query occurs, if it is a long query and the user thinks the system froze, so they close out the app, will that freeze up SQL? Basically, if the lock query is in the middle of a query, and the application who called the query just does a hard exit, does SQL then dispose that thread, or does it freeze it, in return hanging up next threads that are to run after that lock completes?
I have done in prior companies where if a table is currently locked, we alert the end user so they are aware of this and do not think it is an error. Wondering if we should do the same here?
Thanks
I'd like to invoke some cleanup procedure after some INSERT is done, and the cleanup takes a long time. My sql client has very little tolerance on timeouts, so I'd like to return as soon as the command is issued.
I've tried Trigger --the INSERT triggers the stored procedure to do cleanup. The problem is that now the INSERT has to wait for the cleanup to finish in order to return.
I've tried calling a 'proxy' function which then calls the actual cleanup function, but it seems that the function call stack in Postgres is no different than in other languages. The client still waits for the cleanup.
What's the best practice in this scenario? Thanks!
You will have to use an external program to do this. PostgreSQL itself will not allow you to run things in the background. You may be able to handle this with pgAgent or by creating your own program that runs constantly. You will need to send some kind of notification to the program, for which you can use e.g. a table with trigger on the insert, or listen/notify.
I am looking for something like this. Although the syntax is wrong, it demonstrates the principle
foreach(int i in myIntArray)
{
execute mystoredProc i;//this should kick off the proc and go onto next one without waiting for a return value
}
These stored procs are called from a Windows application. I am a little skeptical of creating numerous threads at the application end. I would rather do the threading at the SQL server end. I am open to using SSIS.
You can't do what you're asking for directly.
What you can do is to fire up n threads, and then each thread open up it's own connection, and each connection run it's own SQL query. Each thread will then wait for it's query to return. You can't do this in just one thread.
This also means that you can't do it natively within T-SQL.
You could write a CLR routine that launches multiple threads, and repeat the above process. So enabling your T-SQL to call your CLR code and the CLR deal with the concurrency problem.
But the standard practice for this really is to have multiple client side threads.
If i have a stored procedure or a trigger in Sql Server 2008, can it do some sql calculations 'in another non-blocking thread'? ie. something in the background
also, can two sql code blocks be ran in parallel? or two stored procs be ran in parallel?
for example. Imagine we are given the job calculating the scores for each Stack Overflow user (and please leave all 'do that elsehwere/service/batch/overnight/etc, elswhere) after a user does some 'action'.
so we have a trigger on the Post table, so when a new post is INSERTED, the trigger fires off and part of that logic, it calculates the user's latest score. Instead of waiting for the stored proc to finish and block the current sql thread / executire, can we ask it to calc the score in the background OR parallel.
cheers!
SQL Server does not have parallel or deferred execution: each block of running code in a connection is serial, one line after the other.
To decouple processing, you usually have to use SQL Server Agent jobs or use Service broker. These start executing in a new connection, new session etc
This makes sense:
What if you want to rollback your changes? What does the background thread do and how does it know?
What data does it use? New, Old, lock wait, snapshot?
What if it gets ahead of the main thread and uses stale data?
No, but you could write the request to a queue. Service Broker, a SQL Server component, provides support for this kind of thing. It's probably the best option available for asynchronous processing.
We have a stored procedure that runs nightly that in turn kicks off a number of other procedures. Some of those procedures could logically be run in parallel with some of the others.
How can I indicate to SQL Server whether a procedure should be run in parallel or serial — ie: kicked off of asynchronously or blocking?
What would be the implications of running them in parallel, keeping in mind that I've already determined that the processes won't be competing for table access or locks- just total disk io and memory. For the most part they don't even use the same tables.
Does it matter if some of those procedures are the same procedure, just with different parameters?
If I start a pair or procedures asynchronously, is there a good system in SQL Server to then wait for both of them to finish, or do I need to have each of them set a flag somewhere and check and poll the flag periodically using WAITFOR DELAY?
At the moment we're still on SQL Server 2000.
As a side note, this matters because the main procedure is kicked off in response to the completion of a data dump into the server from a mainframe system. The mainframe dump takes all but about 2 hours each night, and we have no control over it. As a result, we're constantly trying to find ways to reduce processing times.
I had to research this recently, so found this old question that was begging for a more complete answer. Just to be totally explicit: TSQL does not (by itself) have the ability to launch other TSQL operations asynchronously.
That doesn't mean you don't still have a lot of options (some of them mentioned in other answers):
Custom application: Write a simple custom app in the language of your choice, using asynchronous methods. Call a SQL stored proc on each application thread.
SQL Agent jobs: Create multiple SQL jobs, and start them asynchronously from your proc using sp_start_job. You can check to see if they have finished yet using the undocumented function xp_sqlagent_enum_jobs as described in this excellent article by Gregory A. Larsen. (Or have the jobs themselves update your own JOB_PROGRESS table as Chris suggests.) You would literally have to create separate job for each parallel process you anticipate running, even if they are running the same stored proc with different parameters.
OLE Automation: Use sp_oacreate and sp_oamethod to launch a new process calling the other stored proc as described in this article, also by Gregory A. Larsen.
DTS Package: Create a DTS or SSIS package with a simple branching task flow. DTS will launch tasks in individual spids.
Service Broker: If you are on SQL2005+, look into using Service Broker
CLR Parallel Execution: Use the CLR commands Parallel_AddSql and Parallel_Execute as described in this article by Alan Kaplan (SQL2005+ only).
Scheduled Windows Tasks: Listed for completeness, but I'm not a fan of this option.
I don't have much experience with Service Broker or CLR, so I can't comment on those options. If it were me, I'd probably use multiple Jobs in simpler scenarios, and a DTS/SSIS package in more complex scenarios.
One final comment: SQL already attempts to parallelize individual operations whenever it can*. This means that running 2 tasks at the same time instead of after each other is no guarantee that it will finish sooner. Test carefully to see whether it actually improves anything or not.
We had a developer that created a DTS package to run 8 tasks at the same time. Unfortunately, it was only a 4-CPU server :)
*Assuming default settings. This can be modified by altering the server's Maximum Degree of Parallelism or Affinity Mask, or by using the MAXDOP query hint.
Create a couple of SQL Server agent jobs where each one runs a particular proc.
Then from within your master proc kick off the jobs.
The only way of waiting that I can think of is if you have a status table that each proc updates when it's finished.
Then yet another job could poll that table for total completion and kick off a final proc. Alternatively, you could have a trigger on this table.
The memory implications are completely up to your environment..
UPDATE:
If you have access to the task system.. then you could take the same approach. Just have windows execute multiple tasks, each responsible for one proc. Then use a trigger on the status table to kick off something when all of the tasks have completed.
UPDATE2:
Also, if you're willing to create a new app, you could house all of the logic in a single exe...
You do need to move your overnight sprocs to jobs. SQL Server job control will let you do all of the scheduling you are asking for.
You might want to look into using DTS (which can be run from the SQL Agent as a job). It will allow you pretty fine control over which stored procedures need to wait for others to finish and what can run in parallel. You can also run the DTS package as an EXE from your own scheduling software if needed.
NOTE: You will need to create multiple copies of your connection objects to allow calls to run in parallel. Two calls using the same connection object will still block each other even if you don't explicitly put in a dependency.