Posts tagged Linux
When does an Oracle process know it’s on Exadata?
May 4th
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 foreground process, either “cached” (read from disk and put in the database buffercache) or “direct” (read from disk and put in the process’ PGA), or ‘offloaded mode’, where part of the execution is done by the cell server.
Watching the “CopyBack” progress of a new disk on an Exadata compute node
May 3rd
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 we are now awaiting the intermediate “CopyBack” phase.
Exadata and the db_block_checksum parameter.
Apr 6th
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 functions are active inside an executable when there’s a symbol table. And the oracle database executable has a symbol table! One reason to do this, is to get a more granular overview of what the Oracle database is doing than the wait interface, especially to get a more detailed overview of what the database is doing in what is visible in the wait interface as ‘on cpu’.
Observing how Oracle Exadata SmartScans internals work, part 1
Mar 31st
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:
Observing Oracle Exadata SmartScan internals, part 1
Mar 31st
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:
Determine VMWare ESX version from Linux as guest OS
Jan 24th
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:
Oracle 11.2 and the direct path read event
Jan 5th
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”.
Oracle 11.2.0.1 and the ‘kfk: async disk IO’ wait event
Dec 27th
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.
Throttling IO with Linux
Dec 15th
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 Oracle’s popular SQL trace.
