We are using multi-tenant application. Each tenant will have its own schema. Now we need to determine the schema size(Memory Size). Is there a way provided by Spring JPA for this..? How to use Custom JPA Repository for getting the schema size(Memory Size) instead of writing our own implementation?
Spring Data JPA can't help you with that.
And as far as I know, neither can any JPA implementation.
The reason is that all of these tools lack necessary information:
How do you store information in the database. Databases offer lots of storage option, like leaving empty space in blocks to allow for updates that grow rows or compressing data in order to trade storage space for the cost of (de)compressing and many more.
How much data you put in your tables and how it looks like. For example, you probably have many attributes of type String in your model. But how long are they on average? 2 characters? Or 2000?
So for this kind of information you should look more into database tools that might offer this kind of functionality.
Related
I am Working on multiple database like MSSQL server and PostgreSQL with heavy transactions and complex queries. I have searched that simple jdbc is more faster then ORM. I was thinking of using ORM because I do not want to write different query for different database for same work, and also for standardized my dao layer. I am mapping my database tables without using foreign keys and for ORM like apache cayenne I have to map tables with foreign key constraint, so I can use my Joins or any other multiple table operations. Is it good to use and ORM or simple jdbc is fine.
From your problem dscription, you already have an understanding of the tradeoffs involved. So this is really a decision that you need to make for yourself based on those tradeoffs.
My only advice here will be to take a second look at performance requirements. While ORM does introduce an overhead of creating, storing and managing objects, in all but a few cases, you can safely ignore this overhead for the sake of a better abstraction. Also when working with JDBC very often you end up writing your own code to convert ResultSet to objects, which will encounter its own overhead. So you may not end up with faster code, while forfeiting all the benefits of a clean object model and a framework that manages it.
So my own preference is to go with a better abstraction (ORM in this case), and then use the framework tools for optimizing the performance. E.g. to speed up processing of large ResultSets Cayenne provides a few techniques: result iterators, DataRow queries, paginated queries, etc.
On the other hand I would use JDBC or something like MyBatis when it is not possible to cleanly model your data as entities. E.g. when there are no natural relationships, all access happens via stored procedures, etc. Doesn't seem like your case though.
I have integrated the jack rabbit with Oracle database and I am storing the
Data using Jackrabbit, if I don't want to retrieve the data using the
Jackrabbit, in what way I can get the data. In database data is storing in
blob type.
The way Jackrabbit stores the data in the DB is an implementation detail, and it does not magically map this into a "nice" DB schema if that's what you mean. (The hierarchical nature and all the JCR features make this impossible). It's a bit like having a Unix file system and then asking how can I read the low level inodes etc. from the file system implementation - you really should not.
Last but not least note that while it is running nothing else (except for a Jackrabbit cluster setup) must write to the DB (the tables used by Jackrabbit) as this will easily lead to data corruption.
As #TedTrippin already mentioned above, an ORM framework would make things much easier. But if you really want to do it manually in Oracle, the approach would be:
Study the code of the OCM http://jackrabbit.apache.org/jcr/object-content-mapping.html, then get the content according to the logic of associations and relations from Oracle, probably not in one but multiple queries per document; eventually with user-defined functions, which are supported in Oracle and might make things easier.
Would be interesting to know the background of your questions. You tagged it with "Spring" and "CMS". I don't see any reason why you would want to access the data directly from Oracle, it's tedious. In case you want to provide an API for the content to an external system, or in case you have lost a CMS that was once in front of and just using the Jackrabbit repo as a content store, you could still use such ORM / OCM framework standalone to make it easier to access the data.
One of my larger applications is using NHibernate over an Oracle data store. For testing/development, the application uses NHibernate's schema generation to create/re-create the database when needed. Prior to delivery, one of the things being asked of us by the DBAs is to include Comments for each field in the database (there are a lot). I'm looking for solutions that would let me specify the comment in the mapping file. Has anyone done anything like this? Would NHibernate support this activity with a little effort on my end?
Yes, you can use <database-object> to add any additional artifacts (comments, indexes, triggers, etc) that you need.
See 5.6. Auxiliary Database Objects
I am building a DataAccess layer to a DB, what data structure is recommended to use to pass and return a collection?
I use a list of data access objects mapped to the db tables.
I'm not sure what language you're using, but in general, there are tradeoffs of simplicity vs extensibility.
If you return the DataSet directly, you have now coupled yourself to database specific classes. This leaves little room for extension - what if you allow access to files or to other types of data sources? But, it is also very simple. This is the recordset pattern and C#/VB provide a lot of built-in support for this. The GUI layer can access the recordset and easily manipulate the data. This works well for simple applications.
On the other hand, you can wrap the datasets in a custom object, and provide gateway methods (see the Gateway pattern http://martinfowler.com/eaaCatalog/gateway.html). This method is more complex, but provides a lot more extensibility. In a larger application when you need to separate the the business logic, data logic, and GUI logic, this is a more robust way to go.
For larger enterprise applications, you can look into using Object Relational Mapping tools (ORM). They help to automatically map java objects to database tables. They hide a lot of the painful SQL details. Frameworks such as Spring provide excellent support for ORMs.
I tend to use arrays of objects, so that I can disconnect the DAO from the business logic.
You can store the data in the DAO as a dataset, for example, and give them an easy way to add to the database before doing an update, so they can pass in information to do modification operations, and then when they want to commit the changes they can do it in one shot.
I prefer that the user can't add/modify the structure themselves, as it makes it harder to determine what must be changed in the database.
By initially returning an array they can then display what is in the database.
Then, as the presentation layer makes changes, the DAO can be updated by the controller. By having a loose coupling the entire system becomes more flexible, as you can change the DAO from a dataset to something else, and the rest of the application doesn't care.
There are two choices that are the most generic.
The first way to look at a ResultSet is as a List of Maps, where each Map represents a row in the ResultSet. The keys are the columns listed in the FROM clause; the values are the database values.
The second way to look at a ResultSet is as a Map of Lists, where each List represents a column in the ResultSet. The Map keys are the columns listed in the FROM clause; the values are the List of database values.
If you don't want to do full-blown ORM, these can carry you a long way.
I have a daily batch process that involves selecting out a large number of records and formatting up a file to send to an external system. I also need to mark these records as sent so they are not transmitted again tomorrow.
In my naive JDBC way, I would prepare and execute a statement and then begin to loop through the recordset. As I only go forwards through the recordset there is no need for my application server to hold the whole result set in memory at one time. Groups of records can be feed across from the database server.
Now, lets say I'm using hibernate. Won't I endup with a bunch of objects representing the whole result set in memory at once?
Hibernate does also iterate over the result set so only one row is kept in memory. This is the default. If it to load greedily, you must tell it so.
Reasons to use Hibernate:
"Someone" was "creative" with the column names (PRXFC0315.XXFZZCC12)
The DB design is still in flux and/or you want one place where column names are mapped to Java.
You're using Hibernate anyway
You have complex queries and you're not fluent in SQL
Reasons not to use Hibernate:
The rest of your app is pure JDBC
You don't need any of the power of Hibernate
You have complex queries and you're fluent in SQL
You need a specific feature of your DB to make the SQL perform
Hibernate offers some possibilities to keep the session small.
You can use Query.scroll(), Criteria.scroll() for JDBC-like scrolling. You can use Session.evict(Object entity) to remove entities from the session. You can use a StatelessSession to suppress dirty-checking. And there are some more performance optimizations, see the Hibernate documentation.
Hibernate as any ORM framework is intended for developing and maintaining systems based on object oriented programming principal. But most of the databases are relational and not object oriented, so in any case ORM is always a trade off between convenient OOP programming and optimized/most effective DB access.
I wouldn't use ORM for specific isolated tasks, but rather as an overall architectural choice for application persistence layer.
In my opinion I would NOT use Hibernate, since it makes your application a whole lot bigger and less maintainable and you do not really have a chance of optimizing the generated sql-scripts in a quick way.
Furthermore you could use all the SQL functionality the JDBC-bridge supports and are not limited to the hibernate functionality. Another thing is that you have the limitations too that come along with each layer of legacy code.
But in the end it is a philosophical question and you should do it the way it fits you're way of thinking best.
If there are possible performance issues then stick with the JDBC code.
There are a number of well known pure SQL optimisations which
which would be very difficult to do in Hibernate.
Only select the columns you use! (No "select *" stuff ).
Keep the SQl as simple as possible. e.g. Dont include small reference tables like currency codes in the join. Instead load the currency table into memory and resolve currency descriptions with a program lookup.
Depending on the DBMS minor re-ordering of the SQL where predicates can have a major effect on performance.
If you are updateing/inserting only commit every 100 to 1000 updates. i.e. Do not commit every unit of work but keep some counter so you commit less often.
Take advantage of the aggregate functions of your database. If you want totals by DEPT code then do it in the SQL with " SUM(amount) ... GROUP BY DEPT ".