data in client and server - synchronization

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data in client and server - synchronization

Postby ngterry » Sat Sep 17, 2005 4:49 pm

Hi Red1!

Will the data be lost in client for no electricity if the client and server are not in the same machine? Because in my understanding the database is installed in server. How is the mechanism of the client-server synchronization? If there is no such mechanism, is there any solution?

Regards,

Terence
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Postby afalcone » Sun Sep 18, 2005 1:19 am

Hi Terence,

Permit me to express him my point of view al regarding its consultation:

The data are kept in the team where is found lodged the database, by which if the team client remains without electricity, themselves no data is lost, since they are not in that team.
If you has saved you record (press the save button i.e., before being produced the cut of electricity), all those data are stored in the server, not in the client. Its machine client does not store data, but they are stored in the database server machine.

If on the contrary, loses the connection with the server, when you try to record its data will receive an error message that will indicate the impossibility to record its data. In that case will not be able to record them to so much can be connected again with the server.

If client machine is same as database server and is put out, should neither be lost data, therefore of it the same database is entrusted (note that al less oracle and sybase are transactional databases, what guarantees that the transactions are kept complete, not permitting that weaknesses they be generated, this is that be kept part of a transaction and another be not kept).

Best regards,

Alejandro
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Postby ngterry » Sun Sep 18, 2005 10:44 am

Hi Alejandro,

Do you mean the client will write the data in the client's harddisk (the team) before transmitting to the server database? Therefore, the client has a data storage mechanism even no database installed. When the client is facing a cut of electricity, the data in the client will not be lost. Am I right?

Regards,

Terence
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Joined: Thu Sep 01, 2005 11:20 pm

Postby afalcone » Mon Sep 19, 2005 8:19 pm

Hi Terence,

Maintaining the supposition that the database is found in another different machine at client:

Not, the data are not stored in the client. When you save the data (press the save button), the new information is transfered at database server and is stored there (in the server hard disk); the client at no time stores the data in his own hard disk. Supposing that an interruption of electricity in the client be produced, before recording the data (are in the RAM memory of the client), the same are lost.

Even, if you utilize the same machine as the client and database server, if an interruption of electricity is produced before that you have saved the data, the same also are lost. They are avoided sure way when you have indicated to keep; until before of that moment, they are in RAM memory, by which if the machine is put out, they are lost.

When you save the data in systems that utilize databases, is sending a sentence (i.e. UPDATE or INSERT, depending on the case) at server, which takes charge of storing it in said database, that is to say in the hard disk of the machine that acts as server.

Regards,

Alejandro
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Postby ngterry » Thu Sep 22, 2005 12:32 am

Hi Afalcone,

Therefore, in theory if the number of transactions and clients are large, the server will have a delay processing all transactions of so many clients at real time. So the system is exposing to a risk of lossing all data between every transmission and not just one transaction when there is a stop of electricity supply, isn't it?

Regards,

Terence
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Postby afalcone » Thu Sep 22, 2005 1:31 am

Hi Terence,

If that would be able in certain form to be thus.
Nevertheless, it keep in mind that the databases are prepared to process a great number of transactions in real time without greater problems.
Alone they require a lot of memory in the server (to more more comfortable memory they feel they!!!) :lol: .
One of the large advantages exactly to work with databases systems is that they guarantee the integrity of the data, which implies that if a transaction that involves we say 10 different tables, itself complete if all the tables have been brought up to date with said transaction, performing a rollback if some of the updatings in the different tables to failed (that is to say returns behind all the updatings that performed), not permitting that remain data of a transaction kept in partial form.
The data avoid effective way in the database, when all the tables have been able to be brought up to date in a correct way; recently just then is performed the "commit" in the database.
That of course depends on the codification in the system that you are running, but a good codification should be assured to perform the rollback or commit as correspond.

Regards

Alejandro
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