Re: asynchronous or synchronous

Sunny:

In general, synchronous means things are happening in different parts of a system, but they keep track of each other so that none of the parts gets ahead of or behind the other. Asynchronous means each of the parts operate somewhat independently, and at scheduled intervals they will check on each other and take action to get caught up to what each of the other parts have been doing.

With regard to replication, synchronous replication is really turning distributed databases into one big one... guaranteeing transactions are commited or rolled back as a whole... and each of them waits until the other one is ready to go, then they all go. This is referred to as two-phase-commit. First phase is "is everyone sure they will be able to do this?" and then once all the affirmative answers some back, then it says "OK - let's all go ahead and do it".

Asynchronous replication means that logs of events are recorded, and every now and then those events are sent out to other sites to get them up to date. There may be conflicts or problems at the other site, but the sending site has moved ahead anyway. So, there's a good chance at any given time that the sites are not completely in synch. Not so with Synchronous replication.

HTH,
Tom Best

Sunny <sunnyb_at_vendtek.bc.ca> wrote in message news:8lkej5$ub1$1_at_newsfeed.smartt.com...
> Hi everyone
>
> what is asynchronous or synchronous?
> also what is asynchronous or synchronous replication?
>
> Thanks
>
>
>
Received on Tue Jul 25 2000 - 00:00:00 CDT