First of, I apologize if this is the wrong place for this questions, but I haven't found any other location that might help me out.
I have a query that is running on a sql server that keeps running indefinitely and as a result the version store on SQL Server grows and tempdb grows as well. Currently I don't have the source code.
I would like to get a few pointers for where to search for the cause of this problem.
In activity monitor all I see is a process with a taskstate of SUSPENDED, and Wait Type of ASYNC_NETWORK_IO_WRITELOG. I'm running this on SQL Server 2008.
Again sorry if this is the wrong place for asking this.
/Andy.l
First, I've got no experience with SQL2008, but from my experience with SQL2000, it managed itself sometimes into nasty locking situations running multicore environment. I would try rerun query with Option (MAXDOP 1). Cost you almost nothing to check it out.
At least with older SQL Server versions a SELECT could be blocked by other sessions, so I would suspect something like that in your case (even though your mentioning the "version store" which seems to indicate that you have enabled the new snapshot isolation mode).
Running sp_who2 will give you more details about whether it is a blocking problem or not
Related
I have a SQL Server database in production and it has been live for 2 months. A while ago the web application associated with it loading takes too long time. And sometimes it says timeout occurred.
Found a quick fix by running a command 'exec sp_updatestats' will fixed the problem. But I need to be run that one consistently (for every 5 minutes).
So I created a Windows service with timer and started on server. My question is what are the root causes and possible permanent solutions? Anyone?
Here is a Most expensive query from Activity Monitor
WAITFOR(RECEIVE TOP (1) message_type_name, conversation_handle, cast(message_body AS XML) as message_body from [SqlQueryNotificationService-2eea594b-f994-43be-a5ed-d9a47837a391]), TIMEOUT #p2;
To diagnose a poorly performing queries you need to:
Identify the poorly performing query, e.g. via application logging, a SQL Profiler trace filtered to show only queries with a longer duration than a certain threshold etc...
Get an execution plan for the query
At that point you can start to try to figure out what the performance issue is.
Given that exec sp_updatestats fixes your issue it could be that statistics on certain tables are out of date (this is a pretty common cause of performance issues). If thats the case then you might be able to tweak your statistics or at least rebuild only those statistics that are causing issues.
Its worth noting that updating statistics will also cause cached execution plans to become invalid, and so its plausible that your issue is unrelated to statistics - you need to collect more information about the poorly performing queries before looking at solutions.
Your most expensive query looks like its waiting for a message, i.e. its in your list of long running queries because its designed to run for a long time, not because its expensive.
Thanks for everyone i found a solution for my issue . Its quite different I've enabled sql dependency module on my sql server by setting up enable broker on , thats the one causing timeout query so by setting it to false everything is fine working now.
I am working on a Flex application that is connecting via Flash Remoting to ColdFusion 8 with a SQL Server 2005 database. Most of the time, everything runs fine. However, from time to time, it will take an exceptionally long time for SQL Server to return data from a stored procedure call to ColdFusion; returning data from CF to Flex is very fast. When this happens, I can run the exact same call from Management Studio on the SQL Server or a ColdFusion page on the CF server and get results immediately. The most recent occurrence of the issue took about 90 seconds to return data to CF. During the 90 second window, I was able to run the stored procedure in Management Studio several times.
I have tried using different drivers and this doesn't seem to matter. I have also kept an eye on server performance and haven't noticed anything unusual while this is happening. Has anyone seen this behavior before? Any ideas as to what I should be looking for.
While it's working slowly, can you run "sp_who2" against your SQL Server? If it's a blocking issue, you'll see rows that have a value in the "BlkBy" column, meaning that they'r waiting for another process to complete before they can continue.
If that's the case, then there's other troubleshooting to do so you can figure out what's causing the blocks. This article provides an overview of locking and troubleshooting blocks. If that's your issue, please update your question and add more details, and we can help you go from there!
Are you absolutely sure that the query being run in the sp is the same every time? For example, is it possible that when it slows down, the query has a different sort order? Possibly 9 times out of 10, the query returns quickly, and that 10th time is slow b/c the data you're getting is being sorted by some column that isn't indexed?
In these situations, I'd try to have a SQL Trace set up (using sql profiler) and let it run for a while. Once the situation happens, let it run through, and then analyze the trace. Confirm beyond doubt that the query being run is the same as other executions of the same sp
I have RO access on a SQL View. This query below times out. How to avoid this?
select
count(distinct Status)
from
[MyTable] with (NOLOCK)
where
MemberType=6
The error message I get is:
Msg 121, Level 20, State 0, Line 0
A transport-level error has occurred when receiving results from the server (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.)
Your query is probably fine. "The semaphore timeout period has expired" is a Network error, not a SQL Server timeout.
There is apparently some sort of network problem between you and the SQL Server.
edit: However, apparently the query runs for 15-20 min before giving the network error. That is a very long time, so perhaps the network error could be related to the long execution time. Optimization of the underlying View might help.
If [MyTable] in your example is a View, can you post the View Definition so that we can have a go at optimizing it?
Although there is clearly some kind of network instability or something interfering with your connection (15 minutes is possible that you could be crossing a NAT boundary or something in your network is dropping the session), I would think you want such a simple?) query to return well within any anticipated timeoue (like 1s).
I would talk to your DBA and get an index created on the underlying tables on MemberType, Status. If there isn't a single underlying table or these are more complex and created by the view or UDF, and you are running SQL Server 2005 or above, have him consider indexing the view (basically materializing the view in an indexed fashion).
You could put an index on MemberType.
Please check your Windows system event log for any errors specifically for the "Event Source: Dhcp". It's very likely a networking error related to DHCP. Address lease time expired or so. It shouldn't be a problem related to the SQL Server or the query itself.
Just search the internet for "The semaphore timeout period has expired" and you'll get plenty of suggestions what might be a solution for your problem. Unfortunately there doesn't seem to be the solution for this problem.
Do you have an index defined over the Status column and MemberType column?
how many records do you have? are there any indexes on the table? try this:
;with a as (
select distinct Status
from MyTable
where MemberType=6
)
select count(Status)
from a
My team were experiencing these issues intermittently with long running SSIS packages. This has been happening since Windows server patching.
Our SSIS and SQL servers are on separate VM servers.
Working with our Wintel Servers team we rebooted both servers and for the moment, the problem appears to have gone away.
The engineer has said that they're unsure if the issue is the patches or new VMTools that they updated at the same time. We'll monitor for now and if the timeout problems recur, they'll try rolling back the VMXNET3 driver, first, then if that doesn't work, take off the June Rollup patches.
So for us the issue is nothing to do with our SQL Queries (we're loading billions of new rows so it has to be long running).
This is happen because another instance of sql server is running. So you need to kill first then you can able to login to SQL Server.
For that go to Task Manager and Kill or End Task the SQL Server service then go to Services.msc and start the SQL Server service.
While I would be tempted to blame my issues - I'm getting the same error with my query, which is much, much bigger and involves a lot of loops - on the network, I think this is not the case.
Unfortunately it's not that simple. Query runs for 3+ hours before getting that error and apparently it crashes at the same time if it's just a query in SSMS and a job on SQL Server (did not look into details of that yet, so not sure if it's the same error; definitely same spot, though).
So just in case someone comes here with similar problem, this thread:
https://www.sqlservercentral.com/Forums/569962/The-semaphore-timeout-period-has-expired
suggest that it may equally well be a hardware issue or actual timeout.
My loops aren't even (they depend on sales level in given month) in terms of time required for each, so good month takes about 20 mins to calculate (query looks at 4 years).
That way it's entirely possible I need to optimise my query. I would even say it's likely, as some changes I did included new tables, which are heaps... So another round of indexing my data before tearing into VM config and hardware tests.
Being aware that this is old question: I'm on SQL Server 2012 SE, SSMS is 2018 Beta and VM the SQL Server runs on has exclusive use of 132GB of RAM (30% total), 8 cores, and 2TB of SSD SAN.
I have a problem that seems like its a result of a deadlock-situation.
Whe are now searching for the root of the problem but meantime we wanted to restart the server and get the customer going.
And now everytime we start the program it just says "SqlConnection does not support parallel transactions". We have not changed anything in the program, its compiled and on the customers server, but after the "possible deadlock"-situation it want go online again.
We have 7 clients (computers) running the program, each client is talking to a webservice on a local server, and the webservice is talking to the sql-server (same machine as webserver).
We have restarted both the sql-server and the iis-server, but not rebooted the server because of other important services running on the server so its the last thing we do.
We can se no locks or anything in the management tab.
So my question is, why does the "SqlConnection does not support parallel transactions" error comming from one time to another without changing anything in the program and it still lives between sql-restart.
It seems like it happens at the first db-request the program does when it start.
If you need more information just ask. Im puzzled...
More information:
I dont think I have "long" running transactions. The scenario is often that I have a dataset with 20-100 rows (ContractRows) in that Ill do a .Update on the tableAdapter. I also loop throug those 20-100 rows and for some of them Ill create ad-hook-sql-querys (for example if a rented product is marked as returned I create a sql-query to mark the product as returned in the database)
So I do this very simplified:
Create objTransactionObject
Create objtableadapter (objTransactionObject)
for each row in contractDS.contractrows
if row.isreturned then
strSQL &= "update product set instock=1 where prodid=" & row.productid & vbcrlf
End if
next
objtableadapter.update(contractDS)
objData.ExecuteQuery(strSQL, objTransactionObject)
if succsesfull
objtransactionobject.commit
else
objtransactionobject.rollback
end if
objTran.Dispose()
And then Im doing commit or rollback depending on if It went well or not.
Edit: None of the answers have solved the problem, but I'll thank you for the good trouble shooting pointers.
The "SqlConnection does not support parallel transactions" dissapeared suddenly and now the sql-server just "goes down" 4-5 times a day, I guess its a deadlock that does that but I have not the right knowledge to find out and are short on sql-experts who can monitor this for me at the moment. I just restart the sql-server and everything works again. 1 of 10 times I also have to restart the computer. Its really bugging me (and my customers of course).
Anyone knowing a person with good knowledge in analyzing troubles with deadlocks or other sql problems in sweden (or everywhere in the world,english speaking) are free to contact me. I know this is'nt a contact site but I take my chanse to ask the question because I have run out of options, I have spent 3 days and nights optimizing the clients to be sure we close connections and dont do too much stupid things there. Without luck.
It seems to be that you are sharing connections and creating new transactions on the same open connection (this is the parallel part of the exception you are seeing).
Your example seems to support this as you have no mention of how you acquire the connection in it.
You should do a review of your code and make sure that you are only opening a connection and then disposing of it when you are done (and by all means, use the using statement to make sure that you close the connection), as it seems like you are leaving one open somewhere.
Yours doesn't appear to be an unusual problem. Google found a lot of hits when I pasted your error string into the query box.
Reading past answers, it sounds like it has something to do with interleaving transactions improperly or isolation level.
How long are connections held open? Do you have long-running transactions?
Do you have implicit transactions turned on somewhere, so that there are some transactions where you wouldn't have expected them? Have you opened Activity Monitor to see if there are any unexpected transactions?
Have you tried doing a backup of your transaction log? That might clear it out as well if I remember a previous, similar experience correctly.
What is the optimal number of connections that can be open on a SQL Server 2000 DB. I know in the previous company I was working for, on a tru 64 box with Oracle 8i, 8 processor machine we'd figured out that 8*12= 96 connections seemed to be a good number. Is there any such calc for SQL Server 2000. The DB runs on a 2-processor(hyper threaded 4) machine. There are a lot of transactions that run against the DB. The reason I ask is because we have an app that typically tends to leave around 100 connections open even if it is not doing anything and I am having difficulty explaining that that might be a cause for our performance issues. Maybe, SQL Server does not have such a limitation... Can any of you pour forth some wisdom on this? Much appreciate it. Thanks,
I should add it is the Standard Edition.
If you don't know if this is your performance bottleneck then you should be trying to determine that, not trying to limit the connections or something.
If you haven't, you should:
Use SQL Profiler to find long-running queries.
Monitor your db server's cpu load, memory/page file usage, and network usage
Find one of your longest running queries (see #1 above) and write a very lean test app that can throw this query at your db server during peak load and record some response times.
If #1 and #2 don't uncover anything, and #3 shows your db server has slow response times during load then you know you have a problem like "too many connections". But if you haven't done #3 then it seems advisable to do that, as mucking with connection limits and such seems like it will just create artificial bottlenecks, and not really get you to the root of your problem, IMO.
Your performance issue will not be caused by the number of connections.
As well as sliderhouserules' answer, as a quick fix I'd suggest switch off hyperthreading rather than limiting your connections.
link1, link2 (note: this guy worked on the MS SQL 2005 code)
Each connection takes a trivial amount of memory. A shared db lock is for stability only.
This blog post on MSDN indicates there is no limit - at least in the Express editions: http://blogs.msdn.com/euanga/archive/2006/03/09/545576.aspx
And this indicates that it might be 256, for lite editions - http://blogs.msdn.com/stevelasker/archive/2006/04/10/SqlEverywhereInfo.aspx
This also shows no limit: http://channel9.msdn.com/forums/TechOff/169030-The-difference-between-SQL-Server-2005-Express-and-Developer-Edition/?CommentID=299642
addition - from a comment, http://msdn.microsoft.com/en-us/library/aa196730(SQL.80).aspx indicates the max is 32767, while there is no "ideal"
If the app is a long running app and it's on the same server, if the app leaves open db handles that have created a lock this is truly bad for performance. You can check something like select * from sys.dm_tran_locks or sp_lock to give you an idea.