[HACKERS] mvcc and lock

2003-03-23 Thread postgresql 
Hi all
I have read some code on transaction part.
When the new transaction starts, it record the snapshot of database containing the 
current transaction id,etc. So depending on the snapshot
, the transaction decide which tuple is visible.
But transaction could also be implemented by lock. so I am not sure how 
the transaction is implemented, by MVCC or Lock, or by both?
In my option, when tuple is processed in readonly mode(select), MVCC is enough. but 
when tuple is changed, lock is used. I am not sure
whether the explanation is correct.
Thanks for any comments.
Best regards.
josh 



---(end of broadcast)---
TIP 2: you can get off all lists at once with the unregister command
(send unregister YourEmailAddressHere to [EMAIL PROTECTED])

[HACKERS] mvcc and lock

2003-03-18 Thread postgresql 


Hi allI have read some code on transaction part.When the new 
transaction starts, it record the snapshot of database containing the current 
transaction id,etc. So depending on the snapshot, the transaction decide 
which tuple is visible.But transaction could also be implemented by lock. so 
I am not sure how the transaction is implemented, by MVCC or Lock, or by 
both?In my option, when tuple is processed in readonly mode(select), MVCC is 
enough. but when tuple is changed, lock is used. I am not sure whether the 
explanation is correct.Thanks for any comments.Best regards.josh