By default, the database engine automatically takes snapshots in the root container only. Such snapshots cover the root container as well as all open PDBs belonging to it. From version 12.2 onward, you can control whether the database engine automatically takes also PDB-level snapshots through the dynamic initialization parameter AWR_PDB_AUTOFLUSH_ENABLED. In case you want to […]
AWR Flush Levels
From version 12.1.0.2 onward, for taking AWR snapshots, you have the choice between four AWR flush levels: BESTFIT, LITE, TYPICAL and ALL. If you check the Oracle Database documentation, you won’t find much information about the difference between them. The best you will find, in the PL/SQL Packages and Types Reference, is the following: The […]
MIN/MAX Optimization and Asynchronous Global Index Maintenance
In this short post I would like to point out a non-obvious issue that one of my customers recently hit. On the one hand, it’s a typical case where the query optimizer generates a different (suboptimal) execution plan even though nothing relevant (of course, at first sight only) was changed. On the other hand, in […]
V$SQL_CS_HISTOGRAMS: What Are the Buckets’ Thresholds?
The contents of the V$SQL_CS_HISTOGRAM view is used by the SQL engine to decide when a cursor is made bind aware, and therefore, when it should use adaptive cursor sharing. For each child cursor, the view shows three buckets. It is of general knowledge that the first one (BUCKET_ID equal 0) is associated with the […]