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DBA_HIST_ACTIVE_SESS_HISTORY Oracle ASH analysis dashboard showing SQL performance and wait events

DBA_HIST_ACTIVE_SESS_HISTORY: Complete Guide to Oracle ASH Analysis

Posted on by Sanjeeva Kumar

Introduction Have you ever been asked to explain why your Oracle database was slow last Tuesday at 2:30 PM? Or needed to identify which SQL statements were causing CPU spikes during last night’s batch run? This is where DBA_HIST_ACTIVE_SESS_HISTORY becomes your most powerful diagnostic tool. Recently, we faced a production issue where users reported intermittent Read more about DBA_HIST_ACTIVE_SESS_HISTORY: Complete Guide to Oracle ASH Analysis[…]

Oracle Index Fast Full Scan — multiblock I/O across all leaf blocks, no table access

Optimizer Access Paths : Fast Full Scan

Posted on by Sanjeeva Kumar

An index fast full scan reads the entire index as it is i.e. as it exists on the disk. This index read is unsorted. This access path usage multiblock IO to perform the index scan. Index fast full scan simply reads all of the leaf, branch and root block of index quickly using multiblock IO Read more about Optimizer Access Paths : Fast Full Scan[…]

Oracle index full scan traversal path through B-tree index structure from root to leaf blocks

Oracle Index Full Scan: How It Works and When the Optimizer Uses It

Posted on by Sanjeeva Kumar

A production AWR report flagged a query with an INDEX FULL SCAN operation consuming significant I/O. The developer assumed it was an index range scan gone wrong. It was not. The optimizer had a reason — and understanding that reason is what separates reactive troubleshooting from deliberate tuning. This post breaks down what Oracle index Read more about Oracle Index Full Scan: How It Works and When the Optimizer Uses It[…]