Tigran Mkrtchyan wrote:
Does it mean that I have to commit after each select statement?
Here what the manual says:
------------
Description
COMMIT commits the current transaction. All changes made by the
transaction become visible to others and are guaranteed to be durable
if a crash occurs.
-----------
Does select produces some changes?
No, but with autocommit off, you are effectively doing
START TRANSACTION;
SELECT * from x;
and then leaving the transaction open. The way MVCC works is to write
new data into the heap when you insert/update. It doesn't replace the
data. As this select transaction is open, it may still need to read
data from before the update. So VACUUM can't clean that data out of the
table when it runs and the data still needs to be available to that
transaction.
So basically if you have autocommit off, the transaction stays open.
You can either set autocommit on, or you can COMMIT the transaction.
Russell.
Regards,
Tigran.
Tom Lane wrote:
Tigran Mkrtchyan <[EMAIL PROTECTED]> writes:
I got a incorrect or unexpected behavior in concurrent environment.
This is not a bug, nor even surprising. Since you haven't committed
the second transaction, there are a growing number of
dead-but-not-recyclable versions of the updated row. The active client
has to check each of these versions during its primary key uniqueness
check during each update.
regards, tom lane
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