From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru> |
Cc: | Nicolas Barbier <nicolas(dot)barbier(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: What happens If a table changes during a query/procedure execution |
Date: | 2011-03-09 11:15:16 |
Message-ID: | AANLkTinzDh+ev25mWFE5gDEyg-cuqXaZkduftF5nPfSe@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
2011/3/9 Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru>:
> 09.03.2011 18:54, Nicolas Barbier:
>>
>> 2011/3/9 Vlad Arkhipov<arhipov(at)dc(dot)baikal(dot)ru>:
>>
>>
>>>
>>> Let there are two transactions that were created with read commited
>>> isolation level. In the first one we're executing a SELECT query:
>>> SELECT * FROM t UNION ALL SELECT * FROM t;
>>>
>>> In the second transaction we're modifying the same table:
>>> INSERT INTO t DEFAULT VALUES;
>>> COMMIT;
>>>
>>> Is it possible that the last UNION part in the first query will retrieve
>>> not
>>> the same rows as the first one?
>>>
>>
>> No, because statements never see changes made by other transactions
>> while they are in flight.
>>
>>
>
> Is it also true if a statement contains subqueries or function calls? For
> instance,
>
> CREATE FUNCTION f() RETURNS NUMERIC AS $$
> BEGIN
> RETURN (SELECT SUM(a) FROM t);
> END;
> $$ LANGUAGE 'plpgsql';
>
> SELECT a, f() FROM t;
>
> or
>
> SELECT a, (SELECT SUM(a) FROM t) FROM t;
yes, it is same
Regards
Pavel Stehule
>
>
> --
> Sent via pgsql-hackers mailing list (pgsql-hackers(at)postgresql(dot)org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-hackers
>
From | Date | Subject | |
---|---|---|---|
Next Message | Jan Urbański | 2011-03-09 11:20:18 | pl/python - thanks! |
Previous Message | Vlad Arkhipov | 2011-03-09 11:12:53 | Re: What happens If a table changes during a query/procedure execution |