Re: Big project, please help
От | Paul Condon |
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Тема | Re: Big project, please help |
Дата | |
Msg-id | 39413D08.A6BDC664@quiknet.com обсуждение исходный текст |
Список | pgsql-hackers |
Two way replication on a single "table" is availabe in Lotus Notes. In Notes, every record has a time-stamp, which contains the time of the last update. (It also has a creation timestamp.) During replication, timestamps are compared at the row/record level, and compared with the timestamp of the last replication. If, for corresponding rows in two replicas, the timestamp of one row is newer than the last replication, the contents of this newer row is copied to the other replica. But if both of the corresponding rows have newer timestamps, there is a problem. The Lotus Notes solution is to: 1. send a replication conflict message to the Notes Administrator, which message contains full copies of both rows. 2. copy the newest row over the less new row in the replicas. 3. there isa mechanism for the Administrator to reverse the default decision in 2, if the semantics of the message history, or off-line investigation indicates that the wrong decision was made. In practice, the Administrator is not overwhelmed with replication conflict messages because updates usually only originate at the site that originally created the row. Or updates fill only fields that were originally 'TBD'. The full logic is perhaps more complicated than I have described here, but it is already complicated enough to give you an idea of what you're really being asked to do. I am not aware of a supplier of relational database who really supports two way replication at the level that Notes supports it, but Notes isn't a relational database. The difficulty of the position that you appear to be in is that management might believe that the full problem is solved in brand X RDBMS, and you will have trouble convincing management that this is not really true.
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