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Home -> Community -> Usenet -> c.d.o.tools -> Re: replication question
On Mon, 21 Jul 97 05:24:58 GMT, wasim.ahmed_at_cressoft.com.pk (Wasim Ahmed) wrote:
>Hi all,
> A snapshot site (for a replication group) is associated with a single
>master site (for that replicated group). Can a snapshot site be associated
>with more than one master site. Any help will be highly appreciated.
>Wasim Ahmed
>wasim.ahmed_at_cressoft.com.pk
No it cannot.
Currently snapshots are refreshed using ROWIDS as the primary key. The rowid of the row at one master will be different then at another master.
Also, in a multi-master replication situation, updates to rows happen at different times in different places. If a snapshot was to have Site A as its master and site B as its 'secondary' master (it can't, just hypothetical), it might "miss" rows when switching from A to B. Suppose a row was updated at site B. Suppose also that all of the snapshots to site B refreshed, this row would be removed from the snapshot log. Site B now gets around to replicating the change to A (the network from B to A was down for a couple of minutes). That change causes a row to get into site A's snapshot log but you just switched the snapshot from A to B. The snapshot you just switched would 'miss' that row. Any row that was changed on B and not yet propagated to A would potentially be missed during a switchover.
You must rebuild a snapshot to remaster it.
Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Bethesda MD
http://govt.us.oracle.com/ -- downloadable utilities
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