SELECT SUM(bytes) AS bytes FROM dba_data_files;To see the sum of table and index sizes, use this query:
SELECT SUM(bytes) AS bytes FROM dba_segments;The instance size is the sum of memory allocated by the instance. Sign on to SQL*Plus as SYSDBA and issue the following:
SHOW SGAIn most configurations, there is a one-to-one correspondence between instance, server and database. One instance can mount only one database and the instance runs on only one server. If you use Oracle's Real Application Clusters (RAC), you can have one instance running on a server but have mutliple instances (and thus multiple servers) accessing the same database.
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