Does the term 'embedded database' carry different meaning from 'database'?
There are two definitions of embedded databases I've seen:
Embedded database as in a database system particularly designed for the "embedded" space (mobile devices and so on.) This means they perform reasonably in tight environments (memory/CPU wise.)
Embedded database as in databases that do not need a server, and are embedded in an application (like SQLite.) This means everything is managed by the application.
I've personally never seen the term used exactly as Wikipedia defines it, but that's probably my fault, although it resembles quite a bit my number 2 above.
The word 'embedded' does add meaning, basically that the database is dedicated to a specific application rather than shared among multiple applications, to a degree hidden from the user of the application, and completely controlled by the application.
An embedded database is conceptually just a part of the application rather than a separate thing.
Just see the usage of ... for example a H2-embedded database. You don't need a server running on your machine, your whole database ist stored in one (these are originally two) local file. It is opened and locked when you connect to your DB, and it is unlocked when you disconnect.
When a developer embeds a database library inside an application and there is no need for administrator, it is called embedded database. Database is hidden, but data management via SQL (e.g. ITTIA DB SQL) or no SQL (e.g. Berkeley DB) is accessible through APIs. Embedded databases are common for web development or device applications.
Related
I have a SpringBoot application running on a multitenant architecture.
I've two databases Admin and Client (both are MySQL) and both these databases have a User table
Client can add users to the User Table but I need them to get synchronized in the User table of Admin database.
Is there a way I can achieve this?
I've read about flyway migrations but I think it works more on database schema changes and not values.
Please ignore my mistakes as this my first question, any help would be appreciated.
This looks like a solution to your problem:
SymmetricDS is software that replicates relational database tables between multiple databases. It can also be used to replicate files and directories between multiple hosts. It uses a light-weight, web-based protocol to send and receive data, which makes it easy to work with firewalls. Replication is done in the background asynchronously, allowing data changes in offline mode. It supports most commercial and open source database platforms.
How does it work?
Triggers are installed in the database to guarantee that data changes are captured. This means that applications continue to use the database as usual without any special driver software. The triggers are written to be as small and efficient as possible. Routing and syncing of data is done outside of the database in the SymmetricDS process.
SymmetricDS supports many databases and can replicate across different databases, including Oracle, MySQL, MariaDB, PostgreSQL, MS SQL and many more.
https://www.symmetricds.org/docs/faq
You need to create some event from the flow where client adds user to the User Table.
If this "client" flow is in same java service then you can make use of Spring's Asynchronous Event Handling or have a method(which does the data copy) marked with #Async. This ensures the data copy happens in separate thread.
If the "client" flow is in different java service, then any publisher-subscriber model can be used (some opensource frameworks available are kafka, rabbitmq etc).
Now to connect to two datasources at the same time, Spring's RoutingDataSource will come handy in this scenario as it works on "lookup key" to choose the datasource. Or else you can hardcode two datasource beans in your config (since it is fixed in your case).
I am thinking about possibe ways of migrating users between two systems. It is financial system, a web application (Java, Spring, Hibernate, Oracle, JBoss, etc). There are 500k users to migrate together with their data like accounts, contractors, transfers, many others. New application is already working and has 10k users.
Currently I am only thinking about online / offline migration. Online means, that the applications stays accessible to its users during migration, offline means that I turn it off and display technical break message and the migrations is processing. The client doesn't want to turn the application off so it would mean online migration. When the application is on (accessible to its users), many users may perform different operations (also using externals systems) and many background processes are working and changing database data. It would be quite risky to migrate online:
- no database backup as during migration many users would do different things in application, so there would be no point of return,
- problems during migration could block users that are online (database, transaction locks etc).
And maybe you have some strong points to convince my customer that online migration is nonsense? They propably could be divided by the application layer - the Jboss server risks, database risks, business risks..
You're going to have to put your storage (database) in read-only mode during the migration. The application won't be down but some features that alter the data won't be available. During the read-only mode time you copy the data over the new primary site. Once all that data is copied the users must be redirected to the new site and the application becomes read-write again.
If a read-only mode isn't acceptable then you'll have to maintain two databases in sync. Products such as GoldenGate can do that for you.
i have a java project with mysql database
i am using advance installer to create a setup file...
i can embed jre to run the software(Without installing java in the system).
like wise,i want to embed the mysql database (system doesn't contains mysql )...
.There is any software to embed mysql database in my project setup...
MySQL is very difficult to embed correctly and there are a number of failure states that might occur if it is not shut down using the proper procedure. SQLite is a much better engine for this sort of thing and is used by a number of applications as a persistent backing store. While not as powerful as MySQL, it is much more resilient. It also has the advantage of not requiring a separate process.
SQLite's storage method is to persist things into a file that can be copied, moved, or backed-up without any issues. MySQL involves many such files, some of which are in an inconsistent state unless the correct FLUSH is called.
The best you can do with MySQL is bundle it, not embed it, but then you'll be responsible for setting it up on the host system, configuring it correctly, running the appropriate maintenance procedures, and providing some kind of back-up facility for the database itself.
What are the possibilities to distribute data selectively?
I explain my question with an example.
Consider a central database that holds all the data. This database is located in a certain geographical location.
Application A needs a subset of the information present in the central database. Also, application A may be located in a geographical location different (and maybe far) from the one where the central database is located.
So, I thought about creating a new database at the same location of application A that would contain a subset of information of the central database.
Which technology/product allow me to deploy such a configuration?
Thanks
Look for database replication. SQL Server can do this for sure, others (Oracle, MySQL, ...) should have it, too.
The idea is that the other location maintains a (subset) copy. Updates are exchanged incrementally. The way to treat conflicts depends on your application.
Most major database software such as MySql and SQL server can do the job, but it
is not a good model. With the growth of the application (traffic and users),
not only will you create a load on the central database server (which might be serving
other applications),but you will also be abusing your network bandwidth to transfer data
between the far away database and the application server.
A better model is to keep your data close to the application server, and use the far away
database for backup and recovery purposes only. You can use an FC\IP SAN (or any other
storage network architecture) as your storage network model, based on your applications' needs.
One big question that you didn't address is if Application A needs read-only access to the data or if it needs to be read-write.
The immediate concept that comes to mind when reading your requirements is sharding. In MySQL, this can be accomplished with partitioning. That being said, before you jump into partitions, make sure you read up on their pros and cons. There are instances where partitioning can slow things down if your indexes are not well chosen, or your partitioning scheme is not well thought out.
If your needs are read-only, then this should be a fairly simple solution. You can use MySQL in a Master-Slave context, and use App A off a slave. If you need read-write, then this becomes much more complex.
Depending on your write needs, you can split your reads to your slave, and your writes to the master, but that significantly adds complexity to your code structure (need to deal with multiple connections to multiple dbs). The advantage of this kind of layout is that you don't need to have complex DB infrastructure.
On the flip side, you can keep your code as is, and use a Master-Master replication in MySQL. Although not officially supported by Oracle, a lot of people have had success in this. A quick Google search will find you a huge list of blogs, howtos, etc. Just keep in mind that your code has to be properly written to support this (ex: you cannot use auto-increment fields for PKs, etc).
If you have cash to spend, then you can look at some of the more commercial offerings. Oracle DB and SQL Server both support this.
You can also use Block Based data replication, such as DRDB (and Mysql DRDB) to handle the replication between your nodes, but the problem you always will encounter is what happens if your link between the two nodes fails.
The biggest issue you will encounter is how to handle conflicting updates in 2 separate DB nodes. If your data is geographically dependent, then this may not be an issue for you.
Long story short, this is not an easy (or inexpensive) problem to resolve.
It's important to address the possibility of conflicts at the design phase anytime you are talking about replicating databases.
Moving on from that, SAP's Sybase Replication Server will allow you to do just that, either with Sybase database's or 3rd party databases.
In Sybase's world this is frequently called a corporate roll-up environment. There may be multiple geographically seperated databases each with a subset of data which they have primary control over. At the HQ, there is a server that contains all the various subsets in one repository. You can choose to replicate whole tables, or replicate based on values in individual rows/columns.
This keeps the databases in a loosely consistent state. Transaction rates, Geographic separation, and the latency that can be inherent to network will impact how quickly updates move from one database to another. If a network connection is temporarily down, Sybase Replication Server will queue up transaction, and send them as soon as the link comes back up, but the reliability and stability of the replication system will be affected by the stability of the network connection.
Again, as others have stated it's not cheap, but it's relatively straight forward to implement and maintain.
Disclaimer: I have worked for Sybase, and am still part of the SAP family of companies.
I'm working on a school project where the client needs to have multiple users querying and writing to a single data source. The users have access to shared network drives and all functionality has to be in the client application, the IT department won't allow a service to run from one of their servers and external server hosting isn't an option.
The amount of data that actually needs to be stored is actually very little, about 144 rows maximum.
I've looked into using embedded databases, sqllite , hsql , objectdb ... etc but they seem over kill for how little data needs to be saved. It also seemed like with hsql if anyone accessed the database it would be completely locked to any other user. Concurrency wouldn't be much of an issue there will be 5-7 people using the system albeit scarcely only a few times a year.
Would using something like XQuery and serializing everything in xml be a viable option or just simply using the java serializable api?
A distributed, client side database writing files to the shared network drive could be a good solution for this use case. Take a look at Cloud DB, it might be what your looking for.