I am using wildfly-8.2.0.Final.
There are several databases that i have to connect to. However, some of them are only used for certain functionalities on the web application and they are not needed to be online all the time. So when the wildfly starts, some of the datasources may not be online. However, disconnection to any datasource causes wildfly to not deploy .war deployment and i cannot find any way to solve this problem. Is there a way?
UPDATE:
I have a single table on a remote database server. The user will be able to query the table via my web application. The thing is, I have almost no control over the mentioned database. When the web application starts, it could be offline. However, this would cause my web application to fail to start. What I want is being able to run queries on a remote database if it is online. If it is offline, the web page could fail or the query can be canceled. But the only thing that I don’t want is that my web application to be limited by a remote database that I may have no control over.
My previous solution was a workaround. I would run queries on the remote database via a local database which has a foreign table to the remote one. However, the local one reads all data on the remote table before applying any constraints on postgresql 9.5. As the remote table has a large number of rows and I am using lazy loading, it takes so long for a single query and defeats the whole purpose of the lazy loading.
I found a similar question, but there is no answer.
On wildfly, you can set the datasource so that it tries to reconnect periodically when it disconnects. In my case, the deployment should be successful initially for this to be helpful.
The deployment will failed if it references those datasources.
Also you could define but disable those datasources.
Related
we are using 2018.3 version of Tableau Server. The server stats like user login, and other stats are getting logged into PostgreSQL DB. and the same being cleared regularly after 1 week.
Is there any API available in Tableau to connect the DB and take backup of data somewhere like HDFS or any place in Linux server.
Kindly let me know if there are any other way other than API as well.
Thanks.
You can enable access to the underlying PostgreSQL repository database with the tsm command. Here is a link to the documentation for your (older) version of Tableau
https://help.tableau.com/v2018.3/server/en-us/cli_data-access.htm#repository-access-enable
It would be good security practice to limit access to only the machines (whitelisted) that need it, create or use an existing read-only account to access the repository, and ideally to disable access when your admin programs are complete (i.e.. enable access, do your query, disable access)
This way you can have any SQL client code you wish query the repository, create a mirror, create reports, run auditing procedures - whatever you like.
Personally, before writing significant custom code, I’d first see if the info you want is already available another way, in one of the built in admin views, via the REST API, or using the public domain LogShark or TabMon systems or with the Addon (for more recent versions of Tableau) the Server Management Add-on, or possibly the new Data Catalog.
I know at least one server admin who somehow clones the whole Postgres repository database periodically so he can analyze stats offline. Not sure what approach he uses to clone. So you have several options.
I know that using Firebird 2.5+ I can check if there are users accessing my database using SQL, but unfortunately, Firebird 2.0 doesn't have this feature. Yes, I know it's an old version, but it's a legacy software and I'm not allowed to upgrade this in a short time... :(
I need to know if someone is connected to my 2.0 Firebird database, due to a process I'll run:
Block connections to DB (but ONLY if no one is connected)
Run my process
Allow users to reconnect again
I can start my process only when there are no users connected.
My database is part of a client/server system (no Web).
Any hints?
-at[tach] : this parameter prevents any new connections to the database from being made with the exception of the SYSDBA and the database owner. The shutdown will fail if there are any sessions connected after the timeout period has expired. It makes no difference if those connected sessions belong to the SYSDBA, the database owner or any other user. Any connections remaining will terminate the shutdown with the following details:
https://firebirdsql.org/manual/gfix-dbstartstop.html
There is also Services API to do it so your database access library should expose the shutdown function. Specify a short shutdown, and if it failed - then there were some users. If it succeeded - now you can go on with maintenance, having a warranty client applications will not be able to connect.
Alternatively you can upgrade Firebird 2.0 -> 2.1 which is more close to 2.0 than 2.5 but already have Monitoring Tables implemented.
However this your approach has one weak point - race conditions. Using M.T. you envision your work as following:
Keep querying M.T. (which slows down server work significantly) until there are no other connections.
start maintenance work, that would fail if other connections are active
complete maintenance work
Problem is, that even after at step 1 you gained "no other connection" state, it does not mean that between steps 1 and 2, and especially between steps 2 and 3 now new connections would be made.
Even if you made your checks and ensure #1 condition, when you would go on with maintenance there would be some new user connected back and working now. Not every time of course, but as time goes by it will eventually happen one day.
But there is yet one more good thing in FB 2.1 - database-level triggers.
c:\Program Files\Firebird\Firebird_2_1\doc\sql.extensions\README.db_triggers.txt
You can create a regular "all_current_connections" table, using on connect and on disconnect triggers to keep it up to date.
You perhaps would also have to add some logic to your applications, so they would update that table with your internal application ID, to tell main workflow apps/connections from servicing utilities. However it is also possible that mere CURRENT_USER and CURRENT_CONNECTION pair, which the trigger knows and can store to the table, would be enough for that table, if you can infer kind of application from mere user name.
Then on disconnect trigger might be checking whether all "main workflow" apps disconnected and POST_EVENT to notify servicing utilities. However those utilities would still have to shutdown the database first, anyway.
You can shut down the database using gfix. The gfix tool will try to shutdown the database and if connections still exist after a timeout, the shutdown will fail.
For example, use:
gfix -shut -attach 5 <your-database>
This will:
prevent new connection being created,
wait 5 seconds for the existing connections to end,
if after 5 seconds there are still active connections the shutdown will abort,
otherwise, after 5 seconds the database will be shut down.
After shutdown, only SYSDBA or the database owner can create a connection to the database. This is only a viable option if your application it self doesn't use SYSDBA or the database owner account.
You bring the database back online using:
gfix -online <your-database>
For more information, see also Gfix - Database Housekeeping: Database Startup and Shutdown
Well, not an elegant way, but works...
I try to rename the database file.
If there is someone accessing the database, the rename operation will give me
an exception, saying that the file is in use by some process.
If rename succeeds, new users will not be able to access the database
anymore (the connection string used by my systems is not changed).
I run the exclusive process I have to.
Rename the database file to its original name, allowing new users to
connect again.
I post my solution in the hope that helps someone facing a similar problem.
Our new version of the product will probably a Web application and the database was not choosen yet, but certainly will no be Firebird.
Thanks to all that tried to give me an answer.
Has anyone been able to get Camunda to run with Spring Boot and mongodb?
I tried several approaches and always got into a brick wall.
What I tried:
1. jpa / hibernate-ogm
I was able to initiate a connection to mongo after creating my own CamundaDatasourceConfiguration and ProcessEngineConfigurationImpl.
It failed when Camunda tried to get table metadata. I couldn't plug out this behavior.
2. jdbc driver for mongo by progress
I set up the jdbc url and driver class by progress.
Camunda then gets stuck during the startup process and does not get to the point where Jetty is fully started, i.e. the "Jetty started on port XYZ" message in the log.
3. camunda with postgres with mongo FDW
FDW is a mechanism for postress to interface an external datasource. This way an application can work with postgres over jdbc while the FDW will take care of reading and writing the date to the external source, be it a file, mongodb, etc.
After realizing 1 and 2 don't work, I started working on 3.
Has anyone succeeded in doing this and can share how?
so I ran into the same problem and decided to share my answers with you.
Currently it is not possible to run the Camunda-Engine with a NoSQL Database.
In this Camunda-Forum-Post one of the guys at Camunda also says it is not possible to run the engine completely without a database.
And in the offical Camunda-Docs there is also a list with all supported environments. Currently there are only SQL-Databases listed:
https://docs.camunda.org/manual/7.10/introduction/supported-environments/
But in some earlier Blog-Posts they metioned, that they want to make some proof-of-concept examples with the use of NoSQL-Databases. So we can expect, that these databases will be supported in the future, but not at the moment.
(note: the flowable engine is doing the same proof of concepts, they mentioned, that they want to be able to use NoSQL-databases by the end of the next year).
It seems I am running into the Microsoft Distributed Transaction Coordinator (MSDTC) related issue.
SCENARIO
I am using TransactionScope and with in the single scope it hits two different databases on different servers (for instance, DB_A running Windows Server 2003 and DB_B running Windows Server 2008). One database is accessed using Entity Framework 4.0 and another using normal ADO.NET APIs.
When I run the application from my development machine (running WinXP) it commits and rollbacks both the connections accurately. But when I run the application, deployed on another server (for instance WAS_A running Windows Server 2003) it commits correctly but in case of exception is doesn't roll back the database activities on both the servers.
I thought it would be the MSDTC configuration issue on the WAS_A. So I went to the MSDTC -> Security Configuration and checked all the available options (as I did previously on other machines). But still I am facing the same issue.
Looking for your expert advices. :)
I believe that you need to look into Enabling Transaction Flow. Specifically, take a look at how one may error and the other complete as described in TransactionScope and WCF Services:
an error in a second WCF service call was NOT rolling back the changes made in a previous WCF service call...
In order to create an ambient transaction in your client and ensure that it is used by your WCF services...
The article then details the following steps:
Configure Your Binding with transactionFlow
Decorate Your Interface with [TransactionFlow(TransactionFlowOption)]
Decorate Your Method with [OperationBehavior(TransactionScopeRequired)]
Optionally update your Connection Strings with Transaction Binding*
*Note: This is optional in my opinion.
I'm in the process of developing a deployment system for a new web app and I'm wondering where the best point in the process to manage database migrations is (the question of how to do the migrations is another problem entirely).
It seems there are two ways to go:
Use a migration script that can
either be run manually from command
line or as part of the automatic
deployment/build process
Run the migrations when the app
starts up (I'm using ASP.NET so this
can be done easily enough without
causing a long-running user request)
Does anyone have any suggestions/insight/experience with these approaches? Any other suggestions?
I can see why #1 might be more attractive - it gives me complete control over when the DB is updated. However, I quite like #2 as it allows me to quickly iterate between deployments and reduces the manual process. #2 could also be used on my development machine to allow even quicker iterations. Hmm, starting to think having both might be a good thing...
We have a sales-force system with ~100 client and we are updating database at application startup (True, our is a desktop application.) I like this approach, it's safe and iterative if we have indeterministic startpoint (is the client database new or only updated to verison x.y.z?).
But at serverside I'm preferr your #1 option: we create a SQL query file on our virtual machine (based on the copy of the original database) and runs this query against the real server.
So IMHO:
Disconnected clients: startup, iterative scripts
Server: query created on VM based on the actual and real database
So I'm interrested in this problem too, and find some (half)frameworks as RikMigrations. After some googling there is a good startplace about DB versioning/migration frameworks: .NET Database Migration Tool Roundup. Not neccessarely the documentation but the team blogs can be interresting.
I like option #1 better as it seems much more flexible. In lieu of actually performing migrations on each app start, I think I would verify that the database schema (version number?) matches the code, and if not, throw a warning or error about a mismatched database schema.
I'd prefer option #1 for a number of reasons. First, integration tests usually require your DB schema to be up-to-date, and launching a web-site to upgrade the schema will be a huge timewaster. Second, you cannot change database schema while your site is running (say, add a couple of indexes to speed things up).
As for production side of things, upgrading your database in transaction MSI-style installation is much better than attempting to upgrade at each app startup since you can potentially end up with desynchronized database-application versions.
And if you're looking for the migration framework, take a look at Wizardby.
If the application ever has to run on a customer's machine than migrating at startup can prevent a lot of support calls - assuming you can do seamless migration without user intervention (I hope you aren't normally running your web app with permission to modify the database).
If the application always runs under your control automatic migration is less of an issue - but still can be a good feature, especially if you want to minimize downtime and manual deployment steps.