Friday, February 7, 2020

DBA_TABLESPACE_USAGE_METRICS and CDB_TABLES_ACES_USAGE_METRICS

DBA_TABLESPACE_USAGE_METRICS and CDB_TABLESPACE_USAGE_METRICS (starting 12c) provide us summary of space usage of each tablespace including TEMP and UNDO tablespaces. Only different between these 2 views is same as between all other CDB* and DBA* views whereby CDB* views contain information from all PDBs that is viewable from root container and have an extra column CON_ID to correspond each row to a particular PDB. Using this view makes it very easy to analyze space usage. In this article I would explain how to get information from these dictionary views to check the utilization of space within the tablespace(s). You may also want to read my articles about Tablespace space usage history and forecast for 12c and above, and for 11g and 10g.

Friday, January 10, 2020

Adaptive Cursor Sharing


This feature was introduced in 11g release 1 to cater a performance issue caused by bindvariable peeking. Adaptive cursor sharing means that if an SQL is submitted for execution that has bind variables, and it already has an execution plan in shared pool, still optimizer can generate a new execution plan based on the values passed in the bind variable this time. This means that on every call of an SQL, optimizer may use already available plans in the shared pool, or it may generate a new one that is more efficient based on the bind variable values.

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