This question already has an answer here:
EntityManger flushmode in JDBC
(1 answer)
Closed 8 years ago.
entityManager.setFlushMode(FlushModeType.AUTO)
entityManager.setFlushMode(FlushModeType.COMMIT)
What is the difference between above two and what is the advantage of using COMMIT flushMode?
JPA AUTO causes a flush to the database before a query is executed. Simple operations like find don't require a flush since the library can handle the search, however queries would be much more complicated, and so if AUTO is set, it will flush it first. If the mode is set to COMMIT, it will only flush the changes to the database upon a call to commit or flush. If COMMIT is set, and a query is run, it will not return results that have not been flushed.
Source: Another stack overflow question
Related
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 17 days ago.
Improve this question
If I need to perform an automated housekeeping task, and this is my query:
delete from sample_table where id = '1'
And, this scheduled query gets executed from multiple service instances.
Will this have a significant performance impact? What would be an appropriate way of testing this?
Issuing multiple deletes for the same partition can have a significant impact on your cluster.
Remember that all writes in Cassandra (INSERT, UPDATE, DELETE) are inserts under the hood. Since Cassandra does not perform a read-before-write (with the exception of lightweight transactions), issuing a DELETE will insert a tombstone marker regardless of whether the data exists or has already been deleted.
Every single DELETE you issue counts as a write request so depending on how busy your cluster is, it may have a measurable impact on its performance. Cheers!
Erick's answer is pretty solid, but I'd just like to add that the time that you'll likely see performance issues is at read-time. That's because doing a:
SELECT * FROM sample_table WHERE id='1';
...will read ALL of the times that the DELETE was written (tombstones) from the SSTable file. The default settings on a table result in deleted data staying around for 10 days (to ensure proper replication) before they can be picked-up by compaction.
So figure out how many times that DELETE happens per key over a 10 day period, and that's about how many Cassandra will have to reconcile at read-time.
This question already has answers here:
Read Only Database Connection with Hibernate
(3 answers)
Closed 6 years ago.
How can I make my database completely read-only for Hibernate? I don't want Hibernate to be able to change neither table definitions (e.g. create/delete/update tables) nor data in tables. Is there some setting in percictence.xml that makes connection read-only?
Hibernate only does what's asked of it - if you set hibernate.hbm2ddl to auto | update | create | create-drop it will try to modify the DB schema. If you run an insert, it will try to insert data. If you want the DB to be protected against it, assign read-only permissions to the DB user that Hibernate is configured to use.
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 7 years ago.
Improve this question
I think I have to ask my question in another way.
At transactional database which of the following case has been recommended:
writing multi or 2 insert query for saving log of program on DB that has more pressure on server .
writing trigger after inserting for saving log of program on DB that has more pressure on DB.
Thanks for attention.
If you are sure that the insert to the DB will happen only from your application end then I would go for the first option by creating a procedure and include both the INSERT statement in a TRANSACTION block. which will make sure atomic operation.
But, in case there are possibilities that insert to the DB may happen through adhoc query or through third party ETL tool then you have no other option than having a trigger AFTER INSERT TRIGGER to perform the log insert operation (2nd option) since there is no way to call the other INSERT statement automatically or explicitly.
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 7 years ago.
Improve this question
I have a problem with performance of my program.I have a java program that connect to MySql database and do some process witch depend execute SELECT query on database.
Now problem is that my program for process have to execute 130,000 select query on mySql and this need a long of time.
I have 10 minutes for do all process.
Have any idea how do execute 130000 select query maximum in 10 minutes?
Have any idea how do execute 130000 select query maximum in 10 minutes?
It's a 200 queries per second, this should be doable for simple queries. However, the simplest solution is probably to replace them by a single query loading all needed data (you're already assuming that it fits in memory) and process it in Java.
As a HashMap is orders of magnitude faster than any database, the task will become trivial and your machine gets bored.
One Approach is to use InMemory databases Like H2 or HSQL. This Solution will work only if you can pre-load data into memory. Lot of other factors also need to consider like Volume of Data , Frequency of Changes in data in the database etc.
If this is possible, then you can query directly in Memory, which is always faster.
Identify the important data to be loaded to Memory
Create corresponding table structure in Memory DB like H2 Or HSQL
Load those data from your actual MySQL and Insert this in Memory DB
Fire Query in that DB
This question already has answers here:
How to clear all Hibernate cache (ehcache) using Spring?
(7 answers)
Closed 9 years ago.
Recently uses the secondary level cache in my project there
is some issue with it , i wanted to know how can i clear it secondary cache
If you want to clear cache in code you can use:
sf.getCache().evictEntityRegions()
sf.getCache().evictCollectionRegions()
sf.getCache().evictDefaultQueryRegion()
sf.getCache().evictQueryRegions()
where sf means session factory