Just curious, is this expected behaviour?:

mysql> SELECT GREATEST(SLEEP(3),SLEEP(4));
+-----------------------------+
| GREATEST(SLEEP(3),SLEEP(4)) |
+-----------------------------+
| 0 |
+-----------------------------+
1 row in set (8.71 sec)

strawberry wrote:
> Just curious, is this expected behaviour?:
>
> mysql> SELECT GREATEST(SLEEP(3),SLEEP(4));
> +-----------------------------+
>> GREATEST(SLEEP(3),SLEEP(4)) |
> +-----------------------------+
>> 0 |
> +-----------------------------+
> 1 row in set (8.71 sec)

I guess it depends on what can "interrupt" SLEEP?

I would expect
SELECT GREATEST(LOUD_SNORE(),SLEEP(4));
to return 1

Paul Lautman wrote:
> strawberry wrote:
>> Just curious, is this expected behaviour?:
>>
>> mysql> SELECT GREATEST(SLEEP(3),SLEEP(4));
>> +-----------------------------+
>>> GREATEST(SLEEP(3),SLEEP(4)) |
>> +-----------------------------+
>>> 0 |
>> +-----------------------------+
>> 1 row in set (8.71 sec)
>
> I guess it depends on what can "interrupt" SLEEP?
>
> I would expect
> SELECT GREATEST(LOUD_SNORE(),SLEEP(4));
> to return 1
>
>
From the online manual
http://dev.mysql.com/doc/refman/5.0/...function_sleep

SLEEP(duration)

Sleeps (pauses) for the number of seconds given by the duration argument, then
returns 0. If SLEEP() is interrupted, it returns 1. The duration may have a
fractional part given in microseconds. This function was added in MySQL 5.0.12.

So, the results seems to be right.

--

//Aho

strawberry wrote:
> Just curious, is this expected behaviour?:
>
> mysql> SELECT GREATEST(SLEEP(3),SLEEP(4));
> +-----------------------------+
> | GREATEST(SLEEP(3),SLEEP(4)) |
> +-----------------------------+
> | 0 |
> +-----------------------------+
> 1 row in set (8.71 sec)
>
Greatest can't guess the value that a function returns, it has to wait and see
what happens, so it first waits 3 seconds for the first sleep to finish, and
then 4 seconds for the second sleep to finish, none of the sleep functions
will be interrupted (without outer interference) and therefore you get 0.

I think you would see the pattern if you change the sleep values on a mysql
server that runs on a low load machine.

--

//Aho