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Posted by Jerry Stuckle on 02/28/07 18:51
Mitesh wrote:
> Mitesh wrote:
>> Tim Streater wrote:
>>> In article <1172668483.913253.134510@h3g2000cwc.googlegroups.com>,
>>> "Mitesh" <oopsbabies@hotmail.com> wrote:
>>>
>>>> Jerry Stuckle wrote:
>>>>> Michael Fesser wrote:
>>>>>> .oO(Jerry Stuckle)
>>>>>>
>>>>>>> Toby A Inkster wrote:
>>>>>>>
>>>>>>>> You have:
>>>>>>>>
>>>>>>>> $res = mysql_query("SELECT * FROM table1");
>>>>>>>> ...
>>>>>>>> $res = mysql_query("SELECT * FROM table2");
>>>>>>>> if(!$res)
>>>>>>>> return;
>>>>>>>>
>>>>>>>> $res is still going to be set as a result of your first query.
>>>>>>>>
>>>>>>>> Use unset($res) between each query.
>>>>>>> No, Toby.
>>>>>>>
>>>>>>> $res will have the results of the second query. The resource returned
>>>>>>> by the second query (or false) will overwrite what was in $res.
>>>>>> Try that with PDO and it will crash most likely. Overwriting $res will
>>>>>> not necessarily free the previous result set, which might then lead to
>>>>>> MySQL complaining about an unbuffered query or something like that.
>>>>>>
>>>>>> | You cannot use the same variable for a PDOStatement object twice. As
>>>>>> | others have pointed out it works when you set this variable to null in
>>>>>> | between.
>>>>>>
>>>>>> http://bugs.php.net/bug.php?id=35793
>>>>>>
>>>>>> Micha
>>>>> We're not talking PDO , Micha.
>>>>>
>>>>> --
>>>>> ==================
>>>>> Remove the "x" from my email address
>>>>> Jerry Stuckle
>>>>> JDS Computer Training Corp.
>>>>> jstucklex@attglobal.net
>>>>> ==================
>>>> Ok if we need to call, mysql_free_result for mysql resources doesn't
>>>> that mean every other type of resources bound this way to a variable
>>>> must have a freeing function that has to be called before the variable
>>>> can be re-used? So doesn't it coincide with what I am saying that
>>>> variables bound to resources when re-used may cause problems. (and
>>>> according to the others post the variables can be re-used if the
>>>> previously allocated resource is freed)
>>> My understanding was that, if you re-use $res without a call to
>>> mysql_free_result, it re-uses what $res is, which is a pointer to a
>>> result set, but doing that does *not* free up the space used by the
>>> result set. At least that's how it used to be. I don't know if they have
>>> improved the internals such that mysql_free_result is now a dummy call,
>>> or whether that is inherently impossible because mysql itself holds the
>>> result set.
>>>
>>> Perhaps a guru can enlighten us.
>>>
>>> -- tim
>> My concern is not if the previous resource is deallocated or not. I
>> don't have a huge result set returned. It will eventually be freed.
>>
>> What I am really afraid is the working of my current resource pointed
>> to by $res which I have experienced to be not working occasionally as
>> I stated that my second fetch array function suceeds some times and
>> fails other times.
>>
>> Can the following happen?
>>
>> When I overwrite $res variable (whatever the variable maybe a pointer
>> or a reference). Suppose the garbage collector kicks in and finds that
>> the previous resource isn't owned by any variable and tries to free
>> it. When it tries to free, it accesses the $res variable. But now the
>> $res variable owns another resource i.e. my second mysql result set
>> and wrongly frees the second resource hence my second
>> mysql_fetch_array fails.
>>
>> I am sure that I have read that in PHP variables that contain
>> resources are reference variables (similar to pointers) unlike other
>> variables like the $req variable storing a string. We can indded make
>> a variable act like a reference using an ampersand i think.
>>
>> Yes it seems we need a guru here.
>>
>> So my would be question to our guru is can we safely re-use variables
>> that are references?
>>
>> Right now I resolved the situation using two different variable names
>> before I got the suggestion on using mysql_free_result. The product is
>> already shipped and it seems to be working.
>
> Sorry some corrections on my part:
>
> I had in my post said that my second query sometimes succeeds and
> sometimes doesn't. The query succeeds in both occasions however
> mysql_fetch_array sometimes succeeds and sometimes fails.
>
No, the scenario you describe should not happen. If it does, it's a bug
in MySQL. If the resource isn't referenced any more, how would the
garbage collector know to go back to $res, for instance? And if it did,
it would be a bug in PHP.
You never gave us any error messages, etc., so we have no idea what
might have happened.
And BTW - I've done the same many times before, mostly because I forgot
to call mysql_free_result() when writing the code. I've never suffered
any problems because of it.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================
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