In our application, we need to make an exclusive access to a certain place. It is a legacy application with no communication between client and server, all clients communicate directly to the database.
Edit: This is an implementation of a semaphore for sql server
What we were using and working with no problem was this:
using (var sqlConnection = new SqlConnection(Parameters.ConnectionStringUncommited))
{
sqlConnection.Open();
using (var sqlTransaction = sqlConnection.BeginTransaction(IsolationLevel.ReadUncommitted))
{
using (var sqlCommand = new DstSqlCommand($"SELECT COUNT(*) FROM Locks WHERE Id = {IDTOCHECK}", sqlConnection, sqlTransaction))
{
if ((int)sqlCommand.ExecuteScalar() > 0)
ShowMessage("Locked");
else
{
sqlCommand.CommandText = "INSERT INTO Locks(Id) VALUES({IDTOCHECK})";
sqlCommand.ExecuteNonQuery();
// Here we make lot of work, can be locked a lot of time, minutes even, because we show windows and things
// We never commit the transaction, just rollback it
sqlTransaction.Rollback();
}
}
}
}
This was working perfectly with our version using SqlServer 2008 R2 and .NET Framework 3.5. We just made an update and updated to SqlServer 2014 and .NET Framework 4.8 and we are having sometimes timeouts in the SELECT COUNT(*).....statement. The problem is that only happens on our customers, so the debug is very hard.
I really don't get it, the transaction has an isolation level of read uncommited and the code has not changed. What is really happening here?
Just to update this, with sp_getapplock I have no problems, so I mark this as an answer.
There is a weird problem with a deployed Windows application that uses a remote connection string to SQL Server 2012.
When inserting records, the SQL Server times out after a relatively short time saying "The wait operation timed out". I'm not able to debug the deployed application to find out why it is happening and where in the code it is happening.
However, I don't get this error when using the same database on the development machine, with a local connection.
Generally the code used is:
void MapData( SqlTransaction transaction, Dictionary<int, IDataObject> items )
{
foreach ( var i in items )
{
transaction.Save( "CHECKPOINT" );
try
{
ImportItem( transaction, i );
}
catch ( Exception e )
{
transaction.Rollback( "CHECKPOINT" );
}
}
ReportStatus();
}
While this code has been working, I am uncertain about remote connections. We only have this one single case where it does NOT work.
What can it be?
Is there a more solid or performant approach than using Save() and Rollback() in a loop?
I don't want to use TransactionScope to spawn new "child" transactions.
Thanks!
Your transaction is taking too long (not sure if it's committing or rolling back). In order to understand why you'd have to run a trace to get performance metrics.
But to get it working you could increase your timeout. Set the SqlCommand CommandTimeout to a larger value or 0 (no timeout). Also, the connection timeout is used for the transaction timeout - usually an issue only on expensive rollbacks. You specify this in the connection string like Connection Timeout=30.
There are many articles here on EF taking a long time to save, but I've looked through them and used their answers and still seem to get very slow results.
My code looks like so:
using (MarketingEntities1 db = new MarketingEntities1())
{
//using (var trans = db.Database.BeginTransaction(IsolationLevel.ReadUncommitted))
//{
int count = 0;
db.Configuration.AutoDetectChangesEnabled = false;
db.Configuration.ValidateOnSaveEnabled = false;
while (count < ranges.Count)
{
if (bgw != null)
{
bgw.ReportProgress(0, "Saving count: " + count.ToString());
}
db.Set<xGeoIPRanx>().AddRange(ranges.Skip(count).Take(BATCHCOUNT));
db.SaveChanges();
count+=BATCHCOUNT;
}
//trans.Commit();
//}
}
Each batch takes 30+ seconds to complete. BatchCount is 1000. i know EF isn't that slow. You can see that I've stopped using transaction, I've taken tracking off, none of it seemed to help.
Some more info:
xGeoIpRanx is an empty table, with no PK(I'm not sure how much it would help). I'm trying to insert about 10 mil ranges.
Edit:
i feel stupid but im trying to use bulkInsert and i keep getting this entity doesnt exist errors, i look at this code
using (var ctx = GetContext())
{
using (var transactionScope = new TransactionScope())
{
// some stuff in dbcontext
ctx.BulkInsert(entities);
ctx.SaveChanges();
transactionScope.Complete();
}
}
What is "entities" I tried a list of my entities, that doesnt work, what data type is that?
nvm it works as expected it was a strange error due to how i generated the edmx file
Pause the debugger 10 times under load and look at the stack including
external code. Where does it stop most often?
.
Its taking a long time on the .SaveChanges(). just from some quick tests, ADO.net code
That means network latency and server execution time are causing this. For inserts server execution time is usually not that high. You cannot do anything about network latency with EF because it sends one batch per insert. (Yes, this is a deficiency of the framework.).
Don't use EF for bulk work. Consider using table-values parameters or SqlBulkCopy or any other means of bulk inserting such as Aducci's proposal from the comments.
I need some advice regarding an application I wrote. The issues I am having are due to my DAL and connections to my SQL Server 2008 database not being closed, however I have looked at my code and each connection is always being closed.
The application is a multithreaded application that retrieves a set of records and while it processes a record it updates information about it.
Here is the flow:
The administrator has the ability to set the number of threads to run and how many records per thread to pull.
Here is the code that runs after they click start:
Adapters are abstractions to my DAL here is a sample of what they look like:
public class UserDetailsAdapter: IDataAdapter<UserDetails>
{
private IUserDetailFactory _factory;
public UserDetailsAdapter()
{
_factory = new CampaignFactory();
}
public UserDetails FindById(int id){
return _factory.FindById(id);
}
}
As soon as the _factory is called it processes the SQL and immediately closes the connection.
Code For Threaded App:
private int _recordsPerthread;
private int _threadCount;
public void RunDetails()
{
//create an adapter instance that is an abstration
//of the data factory layer
var adapter = new UserDetailsAdapter();
for (var i = 1; i <= _threadCount; i++)
{
//This adater makes a call tot he databse to pull X amount of records and
//set a lock filed so the next set of records that are pulled are differnt.
var details = adapter.FindTopDetailsInQueue(_recordsPerthread);
if (details != null)
{
var parameters = new ArrayList {i, details};
ThreadPool.QueueUserWorkItem(ThreadWorker, parameters);
}
else
{
break;
}
}
}
private void ThreadWorker(object parametersList)
{
var parms = (ArrayList) parametersList;
var threadCount = (int) parms[0];
var details = (List<UserDetails>) parms[1];
var adapter = new DetailsAdapter();
//we keep running until there are no records left inthe Database
while (!_noRecordsInPool)
{
foreach (var detail in details)
{
var userAdapter = new UserAdapter();
var domainAdapter = new DomainAdapter();
var user = userAdapter.FindById(detail.UserId);
var domain = domainAdapter.FindById(detail.DomainId);
//...do some work here......
adapter.Update(detail);
}
if (!_noRecordsInPool)
{
details = adapter.FindTopDetailsInQueue(_recordsPerthread);
if (details == null || details.Count <= 0)
{
_noRecordsInPool = true;
break;
}
}
}
}
The app crashes because there seem to be connection issues to the database. Looking in my log files for the DAL I am seeing this:
Timeout expired. The timeout period
elapsed prior to obtaining a
connection from the pool. This may
have occurred because all pooled
connections were in use and max pool
size was reached
When I run this in one thread it works fine. I am guessing when I runt his in multiple threads I am obviously making too many connections to the DB. Any thoughts on how I can keep this running in multiple threads and make sure the database doesn’t give me any errors.
Update:
I am thinking my issues may be deadlocks in my database. Here is the code in SQL that is running whe I get a deadlock error:
WITH cte AS (
SELECT TOP (#topCount) *
FROM
dbo.UserDetails WITH (READPAST)
WHERE
dbo.UserDetails where IsLocked = 0)
UPDATE cte
SET
IsLocked = 1
OUTPUT INSERTED.*;
I have never had issues with this code before (in other applications). I reorganzied my Indexes as they were 99% fragmented. That didn't help. I am at a loss here.
I'm confused as to where in your code connections get opened, but you probably want your data adapters to implement IDispose (making sure to close the pool connection as you leave using scope) and wrap your code in using blocks:
using (adapter = new UserDetailsAdapter())
{
for (var i = 1; i <= _threadCount; i++)
{
[..]
}
} // adapter leaves scope here; connection is implicitly marked as no longer necessary
ADO.NET uses connection pooling, so there's no need to (and it can be counter-productive to) explicitly open and close connections.
It is not clear to me how you actually connect to the database. The adapter must reference a connection.
How do you actually initialize that connection?
If you use a new adapter for each thread, you must use a new connection for each adapter.
I am not too familiar with your environment, but I am certain that you really need a lot of open connections before your DB starts complaining about it!
Well, after doing some research I found that there might be a bug in SQL server 2008 and running parallel queries. I’ll have to dig up the link where I found the discussion on this, but I ended up running this on my server:
sp_configure 'max degree of parallelism', 1;
GO
RECONFIGURE WITH OVERRIDE;
GO
This can decrease your server performance, overall, so it may not be an option for some people, but it worked great for me.
For some queries I added the MAXDOP(n) (n being the number of processors to utilize) option so they can run more efficiently. It did help a bit.
Secondly, I found out that my DAL’s Dispose method was using the GC.Suppressfinalize method. So, my finally sections were not firing in my DAL properly and not closing out my connections.
Thanks to all who gave their input!
I'm performing a large number of INSERTS to a SQLite database. I'm using just one thread. I batch the writes to improve performance and have a bit of security in case of a crash. Basically I cache up a bunch of data in memory and then when I deem appropriate, I loop over all of that data and perform the INSERTS. The code for this is shown below:
public void Commit()
{
using (SQLiteConnection conn = new SQLiteConnection(this.connString))
{
conn.Open();
using (SQLiteTransaction trans = conn.BeginTransaction())
{
using (SQLiteCommand command = conn.CreateCommand())
{
command.CommandText = "INSERT OR IGNORE INTO [MY_TABLE] (col1, col2) VALUES (?,?)";
command.Parameters.Add(this.col1Param);
command.Parameters.Add(this.col2Param);
foreach (Data o in this.dataTemp)
{
this.col1Param.Value = o.Col1Prop;
this. col2Param.Value = o.Col2Prop;
command.ExecuteNonQuery();
}
}
this.TryHandleCommit(trans);
}
conn.Close();
}
}
I now employ the following gimmick to get the thing to eventually work:
private void TryHandleCommit(SQLiteTransaction trans)
{
try
{
trans.Commit();
}
catch (Exception e)
{
Console.WriteLine("Trying again...");
this.TryHandleCommit(trans);
}
}
I create my DB like so:
public DataBase(String path)
{
//build connection string
SQLiteConnectionStringBuilder connString = new SQLiteConnectionStringBuilder();
connString.DataSource = path;
connString.Version = 3;
connString.DefaultTimeout = 5;
connString.JournalMode = SQLiteJournalModeEnum.Persist;
connString.UseUTF16Encoding = true;
using (connection = new SQLiteConnection(connString.ToString()))
{
//check for existence of db
FileInfo f = new FileInfo(path);
if (!f.Exists) //build new blank db
{
SQLiteConnection.CreateFile(path);
connection.Open();
using (SQLiteTransaction trans = connection.BeginTransaction())
{
using (SQLiteCommand command = connection.CreateCommand())
{
command.CommandText = DataBase.CREATE_MATCHES;
command.ExecuteNonQuery();
command.CommandText = DataBase.CREATE_STRING_DATA;
command.ExecuteNonQuery();
//TODO add logging
}
trans.Commit();
}
connection.Close();
}
}
}
I then export the connection string and use it to obtain new connections in different parts of the program.
At seemingly random intervals, though at far too great a rate to ignore or otherwise workaround this problem, I get unhandled SQLiteException: Database file is locked. This occurs when I attempt to commit the transaction. No errors seem to occur prior to then. This does not always happen. Sometimes the whole thing runs without a hitch.
No reads are being performed on these files before the commits finish.
I have the very latest SQLite binary.
I'm compiling for .NET 2.0.
I'm using VS 2008.
The db is a local file.
All of this activity is encapsulated within one thread / process.
Virus protection is off (though I think that was only relevant if you were connecting over a network?).
As per Scotsman's post I have implemented the following changes:
Journal Mode set to Persist
DB files stored in C:\Docs + Settings\ApplicationData via System.Windows.Forms.Application.AppData windows call
No inner exception
Witnessed on two distinct machines (albeit very similar hardware and software)
Have been running Process Monitor - no extraneous processes are attaching themselves to the DB files - the problem is definitely in my code...
Does anyone have any idea whats going on here?
I know I just dropped a whole mess of code, but I've been trying to figure this out for way too long. My thanks to anyone who makes it to the end of this question!
brian
UPDATES:
Thanks for the suggestions so far! I've implemented many of the suggested changes. I feel that we are getting closer to the answer...however...
The code above technically works however it is non-deterministic! It is not guaranteed to do anything aside from spin in neutral forever. In practice it seems to work somewhere between the 1st and 10th iteration. If i batch my commits at a reasonable interval damage will be mitigated but I really do not want to leave things in this state...
More suggestions welcome!
It looks like you failed to link the command with the transaction you've created.
Instead of:
using (SQLiteCommand command = conn.CreateCommand())
You should use:
using (SQLiteCommand command = new SQLiteCommand("<INSERT statement here>", conn, trans))
Or you can set its Transaction property after its construction.
While we are at it - your handling of failures is incorrect:
The command's ExecuteNonQuery method can also fail and you are not really protected. You should change the code to something like:
public void Commit()
{
using (SQLiteConnection conn = new SQLiteConnection(this.connString))
{
conn.Open();
SQLiteTransaction trans = conn.BeginTransaction();
try
{
using (SQLiteCommand command = conn.CreateCommand())
{
command.Transaction = trans; // Now the command is linked to the transaction and don't try to create a new one (which is probably why your database gets locked)
command.CommandText = "INSERT OR IGNORE INTO [MY_TABLE] (col1, col2) VALUES (?,?)";
command.Parameters.Add(this.col1Param);
command.Parameters.Add(this.col2Param);
foreach (Data o in this.dataTemp)
{
this.col1Param.Value = o.Col1Prop;
this. col2Param.Value = o.Col2Prop;
command.ExecuteNonQuery();
}
}
trans.Commit();
}
catch (SQLiteException ex)
{
// You need to rollback in case something wrong happened in command.ExecuteNonQuery() ...
trans.Rollback();
throw;
}
}
}
Another thing is that you don't need to cache anything in memory. You can depend on SQLite journaling mechanism for storing incomplete transaction state.
Run Sysinternals Process Monitor and filter on filename while running your program to rule out if any other process does anything to it and to see what exacly your program is doing to the file. Long shot, but might give a clue.
We had a very similar problem using nested Transactions with the TransactionScope class. We thought all database actions occurred on the same thread...however we were caught out by the Transaction mechanism...more specifically the Ambient transaction.
Basically there was a transaction higher up the chain which, by the magic of ado, the connection automatically enlisted in. The result was that, even though we thought we were writing to the database on a single thread, the write didn't really happen until the topmost transaction was committed. At this 'indeterminate' point the database was written to causing it to be locked outside of our control.
The solution was to ensure that the sqlite database did not directly take part in the ambient transaction by ensuring we used something like:
using(TransactionScope scope = new TransactionScope(TransactionScopeOptions.RequiresNew))
{
...
scope.Complete()
}
Things to watch for:
don't use connections across multiple threads/processes.
I've seen it happen when a virus scanner would detect changes to the file and try to scan it. It would lock the file for a short interval and cause havoc.
I started facing this same problem today: I'm studying asp.net mvc, building my first application completely from scratch. Sometimes, when I'd write to the database, I'd get the same exception, saying the database file was locked.
I found it really strange, since I was completely sure that there was just one connection open at that time (based on process explorer's listing of active file handles).
I've also built the whole data access layer from scratch, using System.Data.SQLite .Net provider, and, when I planned it, I took special care with connections and transactions, in order to ensure no connection or transaction was left hanging around.
The tricky part was that setting a breakpoint on ExecuteNonQuery() command and running the application in debug mode would make the error disappear!
Googling, I found something interesting on this site: http://www.softperfect.com/board/read.php?8,5775. There, someone replied the thread suggesting the author to put the database path on the anti-virus ignore list.
I added the database file to the ignore list of my anti-virus (Microsoft Security Essentials) and it solved my problem. No more database locked errors!
Is your database file on the same machine as the app or is it stored on a server?
You should create a new connection in every thread. I would simplefy the creation of a connection, use everywhere: connection = new SQLiteConnection(connString.ToString());
and use a database file on the same machine as the app and test again.
Why the two different ways of creating a connection?
These guys were having similiar problems (mostly, it appears, with the journaling file being locked, maybe TortoiseSVN interactions ... check the referenced articles).
They came up with a set of recommendations (correct directories, changing journaling types from delete to persist, etc). http://sqlite.phxsoftware.com/forums/p/689/5445.aspx#5445
The journal mode options are discussed here: http://www.sqlite.org/pragma.html . You could try TRUNCATE.
Is there a stack trace during the exception into SQL Lite?
You indicate you "batch my commits at a reasonable interval". What is the interval?
I would always use a Connection, Transaction and Command in a using clause. In your first code listing you did, but your third (creating the tables) you didn't. I suggest you do that too, because (who knows?) maybe the commands that create the table somehow continue to lock the file. Long shot... but worth a shot?
Do you have Google Desktop Search (or another file indexer) running? As previously mentioned, Sysinternals Process Monitor can help you track it down.
Also, what is the filename of the database? From PerformanceTuningWindows:
Be VERY, VERY careful what you name your database, especially the extension
For example, if you give all your databases the extension .sdb (SQLite Database, nice name hey? I thought so when I choose it anyway...) you discover that the SDB extension is already associated with APPFIX PACKAGES.
Now, here is the cute part, APPFIX is an executable/package that Windows XP recognizes, and it will, (emphasis mine) ADD THE DATABASE TO THE SYSTEM RESTORE FUNCTIONALITY
This means, stay with me here, every time you write ANYTHING to the database, the Windows XP system thinks a bloody executable has changed and copies your ENTIRE 800 meg database to the system restore directory....
I recommend something like DB or DAT.
While the lock is reported on the COMMIT, the lock is on the INSERT/UPDATE command. Check for record locks not being released earlier in your code.