Shared database links are there since Oracle 9iR2, but strangely I have never seen their existence until a customer asked me how to identify in DBA_DB_LINKS (or ALL_) if a database link has been created shared or not…

First, shared database links aim is to reduce number of connection to remote database by sharing same connection link between source and remote by multiple users’ sessions. This can also be seen as a JDBC connections pooling to concentrate multiple session and limit number of real connections onto the database (to obviously save CPU and memory).

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