some questions in postgresql developping

Hello,

I’m a student from Nankai University in China. Now I and my team do a project which aims to integrate XML to Postgresql. What I do is to complete the function of XML Update.

Now I’m researching in concurrency control. I have read the code about the concurrency control for a long time and I’m confident that I know it much. But I am puzzled that why we need to lock tuple. I think locking transaction is sufficient. I don’t think the tuple lock is good at improving executing rate or anything.

I am wishing for your reply.

Best Regards,

--Huang Xiaocheng

--Database & Information System Lab, Nankai University, China