topic Re: Write and Read lock in Application Development and Automation Discussions

Write and Read lock

Former Member — Fri, 09 Jul 2010 05:21:06 GMT

Hi,

I have a query on locking database tables using ENQUEUE-DEQUEUE mechanism. When an entry in a database table is being updated, as I understand a lock can be placed on the entry using u2018ENQUEUEu2019 to restrict multiple users from updating the record. But what happens when a u2018SELECTu2019 is performed on the database table while a lock exists on an entry? Will it result in an exception or will the previous entry be read?

Thanks & Regards,

Amrutha.

Re: Write and Read lock

Former Member — Fri, 09 Jul 2010 06:42:17 GMT

What I have understood from your question is, if a user is entring some values in a table then the lock is applied and the same time you want to read/select values from that table. And you want to knwo that whether you will be able to see the updated values or not??? please correct me if I miss understood.

here is the scenario

suppose I am entring the values and you are selecting the values.

you will be able to see the values which are saved.

example.

I have entered 3 values and saved only 2, in this case if you will select the data from that table then you will be able to see those 2 entries which I made and saved, but not the 3rd one because it is still in LUW not in database.

I hope you are clear with your issue now.

for more details please read lock topic.

Thanks

Lalit Gupta

Re: Write and Read lock

Former Member — Fri, 09 Jul 2010 10:26:42 GMT

hi Amrutha,

there are 3 types of lock modes.

u2022Exclusive Mode: If the data record is locked in exclusive mode, data record can only be edited or displayed by a single user. Another request of executive lock or shared lock is rejected.

u2022Shared Mode: If the data record is locked in shared mode, locked data record can be accessed by other users in display mode. Another request of shared lock is accepted (even if it comes from another user). However, request of exclusive lock is rejected. This is because, only one user can edit or display the record in exclusive lock mode.

u2022Exclusive but not cumulative Mode: Exclusive locks can be requested and processed successfully several times from the same transaction. In contrast, exclusive but not cumulative locks can be called only once from the same transaction. If it is called again from the same transaction, the lock request is rejected.

hope this helps you. now since select statemtnet will only read the lock if someone lock the object in exclusive mode and sends a shared lock request it will be rejected howevre if someone lock the objetc in shared mode and sends a shared lock request it will be accepted.

hope this helps you.

thnaks,

tanmaya

Re: Write and Read lock

Former Member — Fri, 16 Jul 2010 02:09:17 GMT

The lock in sap system have two type lock.

one: sap lock through (ENQUEUE_<lock object name>) and (DEQUEUE_<lock object name>) function

two: database lock ,it is controlled by database system lock mechanism. About database lock , you can read database vender's document.

About details ,you can read ["Relationship Between SAP Locks and Database Locks "|http://help.sap.com/saphelp_nw04/helpdata/en/f4/71aa036c874c308c1a819f05321137/content.htm]