OraNA :: Oracle News Aggregator

This is yet another blogpost on Oracle’s direct path read feature which was introduced for non-parallel query processes in Oracle version 11.

For full table scans, a direct path read is done (according to my tests and current knowledge) when:

- The segment is bigger than 5 * _small_table_threshold.
- (more...)

When an Oracle process starts executing a query and needs to do a full segment scan, it needs to make a decision if it’s going to use ‘blockmode’, which is the normal way of working on non-Exadata Oracle databases, where blocks are read from disk and processed by the Oracle (more...)

This is just a very small post on how to watch the progress of the “CopyBack” state of a freshly inserted disk in an Exadata “Computing” (database) node. A disk failed in the (LSI Hardware) RAID5 set, and the hotspare disk was automatically used. The failed disk was replaced, and (more...)

With Exadata version 11.2.3.2.0 came the Unbreakable Linux Kernel for Exadata, which had been the stock EL5 redhat kernel prior to this version (2.6.18). With the unbreakable kernel came the opportunity to run the perf utility. This utility has the opportunity to see which (more...)

Recently I’ve spoken at the RMOUG training days 2013 in Denver (the mile high city). It was a first time for me to speak for the RMOUG and being in Denver. Thanks to the “sequestration” (federal budget cuts) the lines piled at immigration at Minneapolis (Minneapolis and Saint Paul, the (more...)

In order to look how Exadata smartscans are different, first let’s have a peek the Oracle full segment/multiblock read evolution as short as possible:

a) Traditional multiblock reads, visible via the event ‘db file scattered read’
The essence is: Multiple adjacent blocks are read from disk, and put in the (more...)

Recently I was asked to look at a virtual (linux) system which needed to be moved to a new datacenter. If you want to determine if you are on VM Ware, you can use either lspci or dmidecode. A little searching on the internet revealed it’s reasonably easy to determine the version of VMWare ESX using the BIOS Information:

case $( dmidecode | grep -A4 "BIOS Information" | grep Address | awk '{ print $2 }' ) in
"0xE8480" ) echo "ESX 2.5" ;;
"0xE7C70" ) echo "ESX 3.0" ;;
"0xE7910" ) echo "ESX 3.5" ;;
"0xE7910"  (more...)

In my previous post I touched the topic of a “new” codepath (codepath means “way of utilising the operating system”) for of full segment scans. Full segment scan means scanning a segment (I use “segment” because it could be a partition of a table or index) which is visible commonly visible in an explain plan (but not restricted to) as the rowsources “TABLE ACCESS FULL”, “FAST FULL INDEX SCAN” and “BITMAP FULL SCAN”.

Look at my presentation About multiblock reads to see how and when direct path reads kick in, and what the difference between the two is. Most notably, (more...)

Recently I was discussing some IO related waits with some friends. The wait I was discussing was ‘kfk: async disk IO’. This wait was always visible in Oracle version 11.2.0.1 and seems to be gone in version 11.2.0.2 and above. Here is the result of some investigation into that.

First: the wait is not gone with version 11.2.0.2 and above, which is very simple to prove (this is a database version 11.2.0.3):

SYS@v11203 AS SYSDBA> select name, parameter1, parameter2, parameter3, wait_class from v$event_name where name like 'kfk: async  (more...)

Why?

I guess the first question which comes to mind when reading this title is ‘Why’? For a database, but I guess for any IO depended application, we want IO’s to be faster, not throttle them, alias make them slower. Well, the ‘why’ is: if you want to investigate IO’s, you sometimes want them to slow down, so it’s easier to see them. Also, (not so) recent improvements in the Oracle database made great progress in being able to use the available bandwidth by doing IO in parallel, which could strip away much of the ability to see them in (more...)