[Date Prev][Date Next] [Chronological] [Thread] [Top]

Re: Multimaster further work

On Fri, 1 Nov 2002, Andrew Findlay wrote:
> If we want to give absolute assurance of database consistency across all
> servers, it is essential that all servers receive and acknowledge each
> update *before the result of the operation is returned to the client*.

But for a directory service this level of consistency is usually
considered too stringent and much too costly (in terms of performance).
In the cases I'm familiar with, it is considered best that the service can
converge quickly (O(seconds)) to a consistent state but that brief
inconsistency is permissible.  In a directory, new object attribute values
are almost never dependent on previous values, so strict ordering and
absolute consistency are not necessary.  We are not recalculating bank
balances here.  What *is* strictly necessary is that all masters will
eventually reach the same conclusion as to the correct then-current value.

(For the archive:  this is another reason why directory service !=
general-purpose DBMS.)

Mark H. Wood, Lead System Programmer   mwood@IUPUI.Edu
MS Windows *is* user-friendly, but only for certain values of "user".