Can I adjust the timeout? Yes, go to Preferences, SQL Editor, and adjust the DBMS connection read time out option that defaults to 600 seconds. This sets the maximum amount of time (in seconds) that a query can take before MySQL Workbench disconnects from the MySQL server.
Max value is 1GB. If you set it to more than 1GB, mysql will still start normally, but it will not accept anything over 1GB.
I thought it has been around a little longer, but according to this,
MySQL 5.7.4 introduces the ability to set server side execution time limits, specified in milliseconds, for top level read-only SELECT statements.
SELECT
/*+ MAX_EXECUTION_TIME(1000) */ --in milliseconds
*
FROM table;
Note that this only works for read-only SELECT statements.
Update: This variable was added in MySQL 5.7.4 and renamed to max_execution_time
in MySQL 5.7.8. (source)
If you're using the mysql native driver (common since php 5.3), and the mysqli extension, you can accomplish this with an asynchronous query:
<?php
// Heres an example query that will take a long time to execute.
$sql = "
select *
from information_schema.tables t1
join information_schema.tables t2
join information_schema.tables t3
join information_schema.tables t4
join information_schema.tables t5
join information_schema.tables t6
join information_schema.tables t7
join information_schema.tables t8
";
$mysqli = mysqli_connect('localhost', 'root', '');
$mysqli->query($sql, MYSQLI_ASYNC | MYSQLI_USE_RESULT);
$links = $errors = $reject = [];
$links[] = $mysqli;
// wait up to 1.5 seconds
$seconds = 1;
$microseconds = 500000;
$timeStart = microtime(true);
if (mysqli_poll($links, $errors, $reject, $seconds, $microseconds) > 0) {
echo "query finished executing. now we start fetching the data rows over the network...\n";
$result = $mysqli->reap_async_query();
if ($result) {
while ($row = $result->fetch_row()) {
// print_r($row);
if (microtime(true) - $timeStart > 1.5) {
// we exceeded our time limit in the middle of fetching our result set.
echo "timed out while fetching results\n";
var_dump($mysqli->close());
break;
}
}
}
} else {
echo "timed out while waiting for query to execute\n";
// kill the thread to stop the query from continuing to execute on
// the server, because we are abandoning it.
var_dump($mysqli->kill($mysqli->thread_id));
var_dump($mysqli->close());
}
The flags I'm giving to mysqli_query accomplish important things. It tells the client driver to enable asynchronous mode, while forces us to use more verbose code, but lets us use a timeout(and also issue concurrent queries if you want!). The other flag tells the client not to buffer the entire result set into memory.
By default, php configures its mysql client libraries to fetch the entire result set of your query into memory before it lets your php code start accessing rows in the result. This can take a long time to transfer a large result. We disable it, otherwise we risk that we might time out while waiting for the buffering to complete.
Note that there's two places where we need to check for exceeding a time limit:
You can accomplish similar in the PDO and regular mysql extension. They don't support asynchronous queries, so you can't set a timeout on the query execution time. However, they do support unbuffered result sets, and so you can at least implement a timeout on the fetching of the data.
For many queries, mysql is able to start streaming the results to you almost immediately, and so unbuffered queries alone will allow you to somewhat effectively implement timeouts on certain queries. For example, a
select * from tbl_with_1billion_rows
can start streaming rows right away, but,
select sum(foo) from tbl_with_1billion_rows
needs to process the entire table before it can start returning the first row to you. This latter case is where the timeout on an asynchronous query will save you. It will also save you from plain old deadlocks and other stuff.
ps - I didn't include any timeout logic on the connection itself.
Please rewrite your query like
select /*+ MAX_EXECUTION_TIME(1000) */ * from table
this statement will kill your query after the specified time
You can find the answer on this other S.O. question:
MySQL - can I limit the maximum time allowed for a query to run?
a cron job that runs every second on your database server, connecting and doing something like this:
- SHOW PROCESSLIST
- Find all connections with a query time larger than your maximum desired time
- Run KILL [process id] for each of those processes
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