Thanks for the reply.
I will be a more specific now . Instead of writer , I must say it is a read , modify and then write operation .
The situation is that first I do a SELECT , based on the read data the following instruction can be either INSERT , UPDATE or do nothing, then commit and the close .
When a thread is doing a SELECT , I want to block all the other threads for doing a SELECT on the same table . So I want only one thread to have access to the table at a time . Other threads must wait.
I did some more documentation reading and I noticed that I can use the LOCK command example : LOCK TABLE mytable IN ACCESS EXCLUSIVE MODE . Reason for ACCESS EXCLUSIVE is that there is tip in the documentation that says only ACCESS EXCLUSIVE can block a SELECT.
Am I thinking right ??
Further a question : when doing this way , the Read Committed Isolation level can stay default ??
Thanks
