Couldn't fetch mysqli_result

[nblasgen]

Seems to be the same issue here:

 

http://www.phpfreaks.com/forums/index.php?topic=222008.0

 

So I have what seems to be a very simple query.

 

$q = "SELECT asterisk_local_chan FROM AgentStatus";

$res = $db->query($q);

if ($db->errno) die (__FILE__ . '@' . __LINE__ . ': ' . $db->error);

while (list($channel) = $res->fetch_row())

{

...

}

$res->free();

 

So the query runs fine 99% of the time and trust me on that since I have the query running at least once ever 5 seconds.  But once in a while, the application crashes on:

 

PHP Warning:  mysqli_result::fetch_row(): Couldn't fetch mysqli_result in ... on line 34

PHP Warning:  mysqli_result::free(): Couldn't fetch mysqli_result in ... on line 64

 

So what could possibly cause $db to return a result set ($res) and not trigger an error.  Then when it comes time to read the data set ($res->fetch_row()) the data isn't there.  AgentStatus can get updated by multiple scripts.  I'm thinking maybe it's because of a race condition.  Can anyone speak to that?  Can anyone offer other ideas?

 

And just in case someone suggests it, I don't need to check the result set for !$res->num_rows because fetch_row() will return 0 on no data and the program wont have an issue.  An empty data set can still be free()'ed.

 

[PFMaBiSmAd]

The code in your while(){} loop is likely overwriting the result or your db class is not setting $db->errno under certain conditions. It would take seeing the code in your while(){} loop and the code of your db class to be able to help.

 

Edit: Another possibility would be if your db class contained an error that was destroying the result set under certain conditions, rather than explicit code in the while() loop.

 

Short answer - cannot really help you without full seeing all the relevant code responsible for the symptoms.

[nblasgen]

The $res->fetch_row() is getting a warning itself.  That line comes 2 lines after the query and one line after the check for an error.

 

$q = "SELECT asterisk_local_chan FROM AgentStatus";

$res = $db->query($q);

if ($db->errno) die (__FILE__ . '@' . __LINE__ . ': ' . $db->error);

while (list($channel) = $res->fetch_row())

 

If we're running into errors that quickly I expect it to be another issue.  MySQL (by default) is a non-transaction based database.  My only guess would be that the data is no longer in the database between the time I make the query to the split second later that I fetch the data.

 

But yes, I would love to explore other ideas.  No, I don't think it has to do with overwriting $res or $db within those 3 lines.  Yes, it could be happening somewhere else in the application (I doubt it, but not impossible) but that shouldn't be important.

[PFMaBiSmAd]

... the data is no longer in the database between the time I make the query to the split second later that I fetch the data.

Queries don't work that way. The result set is buffered by php per client connection.