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Conference azur::mcc

Title:	DECmcc user notes file. Does not replace IPMT.
Notice:	Use IPMT for problems. Newsletter location in note 6187
Moderator:	TAEC::BEROUD

Created:	Mon Aug 21 1989
Last Modified:	Wed Jun 04 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	6497
Total number of notes:	27359

3024.0. "Does MCC 1.2.7 always use the DNS master replica? " by WELTM1::CRIDDLE (Graham Criddle, DS Tech Consultant, 853-4015) Tue May 19 1992 08:42

Hi...

While doing some work with MCC 1.2.7 it seems to me that MCC now always
tries to extract information from the DNS clearinghouse containing the master
replica of a directory (ie it does not use the local DNS cache or local read-only
replicas of a directory)

(This would seem to carry on the same behaviour as in MCC_KERNEL_PATCH_3 for 1.1
- note 1267.18 I think)

This supposition is based on the fact that MCC was not able to look at a node4
entity registered in a DNS directory for which there was a readonly copy on the 
local node, but where the DECnet link to the node containing the master copy was
down.

Is this indeed the case?

Rgds,
Graham

T.R	Title	User	Personal Name	Date	Lines
3024.1	MCC reads from a Server but cannot specify which server	TRM::KWAK		`Tue May 19 1992 18:03`	29
	RE: .0 Are you running MCC on VMS or Ultrix? On VMS, the DNS clerk (DNS V1.1) does not cache DNS objects and attributes. When reading an object's attribute values, MCC uses Medium confidence level at the first try. If either the Object or Attribute value does exists, MCC changes the confidence to High and reads the information from the Master Replica. (During MCC registration operation, many attribute values are written to the Master replica, and the changes are sometimes not made to the Read-only replicas - this is an inherent problem in distributed databases. Thus, when the requested information is not found using Medium confidence, the second requested is sent to the Master replica.) When Medium confidence is used, the DNS clerk gets the information from A DNS server, which can be either a server for Read-only replica or a server for Master replica. (I do not know what criteria the DNS clerk uses to select the DNS server. It may be the server's closeness (on the same LAN) or exsisting DECnet link to the server - for more info you can ask NOTES::DNS notes conference) There is no mechanism, available to DNS programming interface, that forces DNS clerk to read from Read-only replica. On Ultrix, MCC does not use "Low confidence" and thus does not use DNS clerk's cache. The Read operation behaves in the similar way as the VMS case. William
3024.2		WELTM1::CRIDDLE	Graham Criddle, DS Tech Consultant, 853-4015	`Wed May 20 1992 08:12`	20
	Hi, William... Thanks for the response.. I am unclear exactly what you are saying here. Is it the case that IF the object/attribute is available when doing a 'medium confidence' lookup then MCC is satisfied with that, or does it do a 'medium level' lookup to check that the object is present, and then does a 'high confidence' read to actually get the attributes it wants from the master replica? My experiments would suggest the latter, and I am trying to get confirmation (or otherwise) of this. Rgds, Graham PS This is on VMS.
3024.3		TRM::KWAK		`Wed May 20 1992 12:59`	17
	RE: .2 MCC usually tries to read an object's attribute value. If DNS returns DNS$_UNKNOWNENTRY (meaning the DNS object does not exist) or the attribute does not exist, then MCC raises the confidence from Medium to High, and reads the attribute value from the Master replica. The unknown attribute case (the attribute does not exist or the attribute value is empty) can happen when you create a Domain and tries to read domain members. The domain object exists, but the attribute (DNS$Members) is empty. This means that when you try to open an empty domain, MCC will always try to read domain membership information (DNS$Members attribute from the Master replica. William