When the Smart Flash Cache was introduced in Exadata, it was caching reads only. So there were only read “optimization” statistics like cell flash cache read hits and physical read requests/bytes optimized in V$SESSTAT and V$SYSSTAT (the former accounted for the read IO requests that got its data from the flash (more...)
This post also applies to non-Exadata systems as hard drives work the same way in other storage arrays too – just the commands you would use for extracting the disk-level metrics would be different.
I just noticed that one of our Exadatas had a disk put into “predictive failure” mode (more...)
This post applies both to non-Exadata and Exadata systems.
Before Oracle 11.2 came out, it was true to say that Oracle Parallel Execution slaves always do direct path reads (bypassing buffer cache) when doing full segment scans. This should not be taken simplistically though. Even when you were doing (more...)
In my previous post ( Advanced Oracle Troubleshooting Guide – Part 11: Complex Wait Chain Signature Analysis with ash_wait_chains.sql ) I introduced an experimental script for analysing performance from “top ASH wait chains” perspective. The early version (0.1) of the script didn’t have the ability to select a (more...)
Advanced Oracle Troubleshooting Guide – Part 11: Complex Wait Chain Signature Analysis with ash_wait_chains.sql
Here’s a treat for the hard-core Oracle performance geeks out there – I’m releasing a cool, but still experimental script for ASH (or poor-man’s ASH)-based wait event analysis, which should add a whole new dimension into ASH based performance analysis. It doesn’t replace any of the existing ASH analysis techniques, (more...)