Sope replication services allow one to create copies of a ZODB continuously in real time. One server is the master, transactions happen on it. The other servers are the slaves, adn get copies of those transactions. Zope Replication services makes it very easy to have high performance read applications. There are multiple servers to service reads. ZRS is also great for reliability. If the master server fails, promote one of the slave servers to become master.
And finally Jim mentions that ZRS can be used to create an object index, on the slave servers, also increasing performance.
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