Re: Connecting to NOTIFY with telnet

Jeff,

On Sat, May 4, 2019 at 2:10 PM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Sat, May 4, 2019 at 3:04 PM Igal Sapir <igal(at)lucee(dot)org> wrote:
>
>> Jeff,
>>
>> On Sat, May 4, 2019 at 11:34 AM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>>
>>> On Sat, May 4, 2019 at 1:49 PM Igal Sapir <igal(at)lucee(dot)org> wrote:
>>>
>>>>
>>>> <snip/>
>>>>
>>>> > A key limitation of the JDBC driver is that it cannot receive
>>>> asynchronous notifications and must poll the backend to check if any
>>>> notifications were issued
>>>>
>>>> Polling is much less efficient than event handling and I'm sure that
>>>> there's a major performance hit with that.
>>>>
>>>
>>> Isn't that addressed here?:
>>>
>>> // If this thread is the only one that uses the
>>> connection, a timeout can be used to
>>> // receive notifications immediately:
>>> // org.postgresql.PGNotification notifications[] =
>>> pgconn.getNotifications(10000);
>>>
>>>
>> It "helps", but it's still not the same as keeping the connection open
>> and receiving messages in real time.
>>
>
> But it is the same as that. It keeps the connection open, and receives
> the messages in real time. It blocks either until it gets a NOTIFY, or for
> 10 seconds, whichever occurs first. You can use 0 to block forever until a
> NOTIFY arrives. Maybe you didn't remove the sleep a few lines further
> down? Or is there some other problem here?
>

I didn't try it out, but I know from experience with other systems that
long polling is not as efficient as asynchronous events over an open
socket. For example, Comet vs. WebSockets in web servers.

The only way to find out how big, or small, the impact is, is to benchmark
both implementations, but I have no doubt that the open socket will be more
efficient.

Best,

Igal