I have a JSP/Spring application using Hibernate/JPA connected to a database. I have an external program that check if the web server is up every 5 minutes.
The program call a specific URL to check if the web server is still running. The server returns "SUCCESS". Obviously if the server is now, nothing is returned. The request timesout and an alert is raised to inform the sysadmin that something is wrong...
I would like to add another layer to this process: I would like the server to return "ERROR" if the database server is down. Is there a way using Hibernate to check if the database server is alive and well?
What I tought to do was to take an object and try to save it. This would work, but I think it's probably too much for what I want. I could also read(load) an object from the database. But since we use second-level caching for all our objects, the object will be loaded from the cache, and not the database.
What I'm looking for is something like:
HibernateUtils.checkDatabase()
Does such a function exist in Hibernate?
You could use a native query, e.g.
Query query = sess.createNativeQuery("select count(*) from mytable").setCacheable(false);
BigDecimal val = (BigDecimal) query.getSingleResult();
That should force hibernate to use a connection from the pool. If the db is down, I don't know exactly what will be the error returned by hibernate given that it can't get the connection from the pool. If the db is up, you get the result of your query.
Related
I have a Python package that I am able to run successfully on an Azure Data Science Virtual Machine. However, when I push it to Azure as a Function, I cannot successfully make a database connection. I was getting an error that the ODBC Driver 13 for SQL Server was not supported, so I changed the driver to ODBC Driver 17 for SQL Server and now I am NOT getting an error, but no data is being returned for a query that I know should return data.
Is there any other reason that data would not be returned? Firewall issues? do I need to add a binding? Do I need to separate out the connection string to feed each part (e.g., Driver, UID, PWD) into pyodbc.connect() separately? Right now I am feeding it in like this:
setting = os.environ("CONNECTIONSTRING")
conn = pyodbc.connect(setting)
This query works fine returning data when I run it on the VM using this code, just not as a Function.
(Note, this is different from my previous post regarding reading the Azure App Setting. That problem has been solved).
There are many parts where this could be breaking.
I'd suggest start by having a Profiler or Extended Events trace on your SQL Server to verify whether a connection is even being established. If not then you need to work through the the various points of connectivity to find out where it breaks. The identity, firewall, NSGs etc might all come into play here.
Once you see a connection then you can play with permissions to ensure that your query then returns your data.
Without a full picture of your infrastructure and settings it is hard to pin it down further.
Turns out it was not a database connectivity issue like I thought it was; it was a code error.
I am developing a Servlet applicaiton. It obtains a database connection from the connection pool supported by the Tomcat container to query and update database data.
I run into a problem. The Servlet gets a database connection and then add a new table row or delete a table row. After that, it commits the change. Later, a connection is obtained to execute queries. I find that the data returned from the queries using the second connection do not reflect the change made with the first database connection.
Isn't it strange? The changes made with the first database connection have been committed successfully. Why the new rows inserted do not appear in the later query? Why the rows deleted still appear in the later query?
Does it relate to the setting of transaction level?
Can anyone help?
03-12: More Information (#1):
I use MySQL Community Server 5.6.
My servlet runs on Tomcat 7.0.41.0.
The Resource element in the conf/server.xml is as follows:
<Resource type="javax.sql.DataSource"
name="jdbc/storewscloud"
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/myappdb"
maxActive="100"
minIdle="10"
maxWait="10000"
initialSize="10"
removeAbandonedTimeout="60"
removeAbandoned="true"
logAbandoned="true"
username="root"
password="xxxxxxxxxx"
/></li>
I do not use any cache explicitly.
Every time the servlet gets a database connection, it turns the auto-commit mode of the connection off.
When the servlet is invoked, a database connection is obtained. The servet uses it to update data in the database. After that, it commits the changes. Then, it uses Apache HttpClients to invoke the same servlet to do some other thing which also obtains a database connection and execute query. The later query returns 'old' data. If I refresh the web page, the latest data are shown. It looks like some party, mysql jdbc driver or connection object, cache the data somewhere. I have no clue.
03-12: More Information (#2):
I did an experiment getting a connection without using the connection pool. The result is correct. So, the problem is caused by the connection pool.
To make the query return right data using the 2nd connection from the pool, I need to not only commit the data changes using the 1st connection from the pool but also CLOSE the 1st connection.
It seems that the data changes made are not completely saved in the database even the commit() is called until the close() is called.
Why?
I found that there is a new version of C3P0 connection pool released recently. I gave it a try. It works! The problems I had do not occur. Therefore, I use it to replace the bundled connection pool of the Tomcat server. For those who encounter the same problem as I do, C3P0 maybe a solution for you too.
C3P0 Project URL
I have 3 servers set up for SQL mirroring and automatic failover using a witness server. This works as expected.
Now my application that connects to the database, seems to have a problem when a failover occurs - I need to manually intervene and change connection strings for it to connect again.
The best solution I've found so far involves using Failover Partner parameter of the connection string, however it's neither intuitive nor complete: Data Source="Mirror";Failover Partner="Principal" found here.
From the example in the blog above (scenario #3) when the first failover occurs, and principal (failover partner) is unavailable, data source is used instead (which is the new principal). If it fails again (and I only tried within a limited period), it then comes up with an error message. This happens because the connection string is cached, so until this is refreshed, it will keep coming out with an error (it seems connection string refreshes ~5 mins after it encounters an error). If after failover I swap data source and failover partner, I will have one more silent failover again.
Is there a way to achieve fully automatic failover for applications that use mirroring databases too (without ever seeing the error)?
I can see potential workarounds using custom scripts that would poll currently active database node name and adjust connection string accordingly, however it seems like an overkill at the moment.
Read the blog post here
http://blogs.msdn.com/b/spike/archive/2010/12/15/running-a-database-mirror-setup-with-the-sqlbrowser-service-off-may-produce-unexpected-results.aspx
It explains what is happening, the failover partner is actually being read from the sql server not from your config. Run the query in that post to find out what is actually being used as the failover server. It will probably be a machine name that is not discoverable from where your client is running.
You can clear the application pool in the case a failover has happened. Not very nice I know ;-)
// ClearAllPools resets (or empties) the connection pool.
// If there are connections in use at the time of the call,
// they are marked appropriately and will be discarded
// (instead of being returned to the pool) when Close is called on them.
System.Data.SqlClient.SqlConnection.ClearAllPools();
We use it when we change an underlying server via SQL Server alias, to enforce a "refresh" of the server name.
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.clearallpools.aspx
The solution is to turn connection pooling off Pooling="false"
Whilst this has minimal impact on small applications, I haven't tested it with applications that receive hundreds of requests per minute (or more) and not sure what the implications are. Anyone care to comment?
Try this connectionString:
connectionString="Data Source=[MSSQLPrincipalServerIP,MSSQLPORT];Failover Partner=[MSSQLMirrorServerIP,MSSQLPORT];Initial Catalog=DatabaseName;Persist Security Info=True;User Id=userName; Password=userPassword.; Connection Timeout=15;"
If you are using .net development, you can try to use ObjAdoDBLib or PigSQLSrvLib and PigSQLSrvCoreLib, and the code will become simple.
Example code:
New object
ObjAdoDBLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd, Me.ProviderSQLSrv)
PigSQLSrvLib or PigSQLSrvCoreLib
Me.ConnSQLSrv = New ConnSQLSrv(Me.DBSrv, Me.MirrDBSrv, Me.CurrDB, Me.DBUser, Me.DBPwd)
Execute this method to automatically connect to the online database after the mirror database fails over.
Me.ConnSQLSrv.OpenOrKeepActive
For more information, see the relevant links.
https://www.nuget.org/packages/ObjAdoDBLib/
https://www.nuget.org/packages/PigSQLSrvLib/
https://www.nuget.org/packages/PigSQLSrvCoreLib/
I have a bunch of stored procs doing the business logic job in a SQL Server instance within a web application. When something goes wrong all of them queue a message in a specific table (let's say 'warnings') keeping track of the error severity and issue description. I want the web application using the stored procs to be able to query the message table at the end of the run but getting a list of the proper message only, i.e. the message created during the specific session or that specific connection: so I am in doubt if
have the web application send to the db a guid to INSERT as column value in the message records (but somehow I have to keep track of it in several stored procs running at the page level, so I need something "global")
OR
if I can use some id related to the connection opened by the application - and this would be definitely more sane. Something like (this is pseudo code):
SELECT #sessionid = sessionid FROM sys.something where this = that
Have some hints?
Thanks a lot for your ideas
To retrieve your current SessionId in SQL Server you can simply execute the following:
select ##SPID
See:
http://msdn.microsoft.com/en-us/library/ms189535.aspx
We have a classic ASP application that simply works and we have been loathe to modify the code lest we invoke the wrath of some long-dead Greek gods.
We recently had the requirement to add a feature to an application. The feature implementation is really just a database operation requires minimal change to the UI.
I changed the UI and made the minor modification to submit a new data value to the sproc call (sproc1).
In sproc1 that is called directly from ASP, we added a new call to another sproc that happens to be located on another server, sproc2.
Somehow, this does not work via our ASP app, but works in SQL Management Studio.
Here's the technical details:
SQL 2005 on both database servers.
Sql Login is authenticating from the ASP application to SQL 2005 Server 1.
Linked server from Server 1 to Server 2 is working.
When executing sproc1 from SQL Management Studio - works fine. Even when credentialed as the same user our code uses (the application sql login).
sproc2 works when called independently of sproc1 from SQL Management Studio.
VBScript (ASP) captures an error which is emitted in the XML back to the client. Error number is 0, error description is blank. Both from the ADODB.Connection object and from whatever Err.Number/Err.Description yields in VBScript from the ASP side.
So without any errors, nor any reproducibility (i.e. through SQL Mgmt Studio) - does anyone know the issue?
Our current plan is to break down and dig into the code on the ASP side and make a completely separate call to Server 2.sproc2 directly from ASP rather than trying to piggy-back through sproc1.
Have you got set nocount on set in both stored procedures? I had a similar issue once and whilst I can't remember exactly how I solved it at the moment, I know that had something to do with it!
You could be suffering from the double-hop problem
The double-hop issue is when the ASP/X page tries to use resources that are located on a server that is different from the IIS server.
Windows NT Challenge/Response does not support double-hop impersonations (in that once passed to the IIS server, the same credentials cannot be passed to a back-end server for authentication).
You should verify the attempted second connection using SQL Profiler.
Note that with your manual testing you are not authenticating via IIS. It's only when you initiate the sql via the ASP/X page that this problem manifests.
More resources:
http://support.microsoft.com/kb/910449
http://support.microsoft.com/kb/891031
http://support.microsoft.com/kb/810572
I had a similar problem and I solved it by setting nocount on and removing print commands.
My first reaction is that this might not be an issue of calling cross-server, but one of calling a second proc from a first, and that this might be what's acting differently in the two different environments.
My first question is this: what happens if you remove the cross-server aspect from the equation? If you could set up a test system where your first proc calls your second proc, but the second proc is on the same server and/or in the same database, do you still get the same problem?
Along these same lines: In my experience, when the application and SSMS have gotten different results like that, it has often been an issue of the stored procedures' settings. It could be, as Luke says, NOCOUNT. I've had this sort of thing happen from extraneous PRINT statements in the code, although I seem to remember the PRINTed value becoming part of the error description (very counterintuitively).
If anything is returned in the Messages window when you run this in SSMS, find out where it is coming from and make it stop. I would have to look up the technical terms, but my recollection is that different querying environments have different sensitivities to "errors", and that a default connection via SSSM will not throw an error at certain times when an ADO connection from a scripting language will.
One final thought: in case it is an environment thing, try different settings on your ASP page's connection string. E.g., if you have an OLEDB connection, try ODBC. Try the native and non-native SQL Server drivers. Check out what connection string options your provider supports, and try any of them that seem like they might be worth trying.
Example code might help :) Are you trying to return two tables from the stored procedure; I don't think ADO 2.6 can handle multiple tables being returned.
I did consider that (double-hop), but what is the difference between a sproc-in-a-sproc call like I am referring to vs. a typical cross-server join via INNER JOIN? Both would be executed on Server1, using the Linked Server credentials, and authenticating to Server 2.
Can anyone confirm that calling a sproc cross-server is different than doing a join on data tables? And why?
If the Linked Server config is a sql account - is that considered a double-hop (since what you refer to is NTLM double-hops?)
In terms of whether multiple resultsets are coming back - no. Both Server1.Sproc1 and Server2.Sproc2 would be "ExecuteNonQuery()" in the .net world and return nothing (no resultsets and no return values).
Try to check the permissions to the database for the user specified in the connection string.
Use the same user name in the connection string to log in to the database while using sql mgmt studio.
create some temporary table to write the intermediate values and exceptions since it can be a effective way of debugging your application.
Can I just check: You made the addition of sproc2? Prior to that it was working fine for ages.
Could you not change where you call sproc2 from? Rather than calling it from inside sproc1, can you call it from the ASP? That way you control the authentication to SQL in the code, and don't have to rely on setting up any trusts or shared remote authentication on the servers.
How is your linked server set up? You generally have some options as to how it authenticates to the remote server, which include logging in as the currently logged in user or specifying a SQL login to always use. Have you tried setting it to always use a specific account? That should eliminate any possible permissions issues in calling the remote procedure...