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Re: Why does Statement.close() close result set?

From: Peter Kovacs <peter(dot)kovacs(at)siemens(dot)com>
To: Kevin Schmidt <kevin(dot)schmidt(at)enterworks(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-jdbc(at)postgresql(dot)org,erserver-general(at)svr3(dot)postgresql(dot)org
Subject: Re: Why does Statement.close() close result set?
Date: 2003-10-10 15:46:20
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-jdbc
And about ResultSet the API documentation says:

"A |ResultSet| object is automatically closed when the |Statement| 
object that generated it is closed, re-executed, or used to retrieve the 
next result from a sequence of multiple results."

This implies that there is (should be) no valid ResultSets for a 
Statement other than the "current" ResultSet. This completes the passage 
quoted below.


Kevin Schmidt wrote:

> Tom,
> A ResultSet object is closed when it's Statement object is closed per 
> the JDBC spec.  Look at the Javadoc on Statement.close() and it states 
> "When a Statement object is closed, its current ResultSet object, if 
> one exists, is also closed."  At a higher level it also says that 
> close "Releases this Statement object's database and JDBC resources 
> immediately ..." and the ResultSet is one of those resources.
> Kevin
> Tom Lane wrote:
>> I've been trying to get erserver to work with the current JDBC driver,
>> and finding that it doesn't work very well.  The problem is that there
>> are many places in which a function creates a Statement, executes it
>> to get a ResultSet, closes the Statement, and returns the ResultSet to
>> its caller.  This pattern worked okay in JDBC 7.0, but it fails
>> completely with the current driver, because Statement.close() thinks
>> it should close the last result set returned by the statement.
>> I've been able to sort-of work around this by commenting out the
>> explicit close calls, but this doesn't really work, because the
>> created Statement object has no references once control has left
>> the calling function.  A garbage-collection pass would finalize the
>> Statement and thereby zap the ResultSet, whether or not there are
>> still any valid references to the ResultSet.
>> The above programming pattern seems perfectly valid to me, and
>> accordingly I think that Statement.close() is broken.  The current
>> behavior foregoes all the advantages of Java's memory management model
>> and turns them into liabilities.  Instead of letting garbage collection
>> do what it's supposed to, the programmer is forced to hang onto
>> references to one object in order to preserve the validity of a
>> different object.
>> Comments?
>>             regards, tom lane
>> BTW, the error reported by in this situation is
>> extremely misleading; it gripes about "connection closed" when it
>> should say "result set closed".
>> ---------------------------(end of broadcast)---------------------------
>> TIP 8: explain analyze is your friend
> ---------------------------(end of broadcast)---------------------------
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