Exadata

fritshoogland's picture

OBUG Tech Days Belgium 2019 – Antwerp – 7/8-FEB-2019

Agenda: https://www.techdaysbelgium.be/?page_id=507

Dates: February 7 and 8, 2019

Location: http://cinemacartoons.be in Antwerp, Belgium

More information soon.

For people from the netherlands: this is easy reachable by car or by train! This is a chance to attend a conference and meet up with a lot of well-known speakers in the Oracle database area without too extensive travelling.

fritshoogland's picture

opatch investigations

This blogpost is about opatch and how to obtain information about the current oracle home(s), and how to obtain information about the patches to be applied.

Patches that can be applied using opatch are provided by oracle as zip files which have the following naming convention:
p[patchnumber]_[baseversion]_[platform]-[architecture].zip. The patch normally contains an XML file called ‘PatchSearch.xml’ and a directory with the patch number. Inside the patch number directory there is a README.txt which is lame, because it says ‘Refer to README.html’, and a README.html that contains the readme information that is also visible when the [README] button for this patch is selected in MOS.

fritshoogland's picture

opatch versions

This blogpost is about oracle’s patching tool for the database and grid infrastructure: opatch. I personally have a love/hate relationship with opatch. In essence, opatch automates a lot of things that would be very error prone if it were to be done by hand, which is a good thing. However, there are a lot of things surrounding opatch that I despise. An example of that is the version numbering of opatch itself.

Versions and more versions

To jump into the matter directly: versions. I don’t understand why this has to be this complicated. I would even go as far as saying that somebody needs to step in and clean this up.

Richard Foote's picture

FIRST_ROWS_10 CBO Is Hopeless, It’s Using The Wrong Index !! (Weeping Wall)

There’s an organisation I had been dealing with on and off over the years who were having all sorts of issues with their Siebel System and who were totally convinced their performance issues were due directly to being forced to use the FIRST_ROWS_10 optimizer. I’ve attempted on a number of occasions to explain that their […]

fritshoogland's picture

Oracle wait event ‘TCP Socket (KGAS)’

I was asked some time ago what the Oracle database event ‘TCP socket (KGAS)’ means. This blogpost is a deep dive into what this event times in Oracle database 12.1.0.2.180717.

This event is not normally seen, only when TCP connections are initiated from the database using packages like UTL_TCP, UTL_SMTP and the one used in this article, UTL_HTTP.

A very basic explanation is this event times the time that a database foreground session spends on TCP connection management and communicating over TCP, excluding client and database link (sqlnet) networking. If you trace the system calls, you see that mostly that is working with a (network) socket. Part of the code in the oracle database that is managing that, sits in the kernel code layer kgas, kernel generic (of which I am quite sure, and then my guess:) asynchronous services, which explains the naming of the event.

fritshoogland's picture

All about headroom and mandatory patching before June 2019

This post was triggered upon rereading a blogpost by Mike Dietrich called databases need patched minimum april 2019. Mike’s blogpost makes it clear this is about databases that are connected using database links, and that:
– Newer databases do not need additional patching for this issue (11.2.0.4, 12.1.0.2, 12.2 and newer).
– Recent PSU patches contain a fix for certain older versions (11.1.0.7, 11.2.0.3 and 12.1.0.1).
– This means versions 11.2.0.2 and earlier 11.2 versions, 11.1.0.6 and earlier and anything at version 10 or earlier can not be fixed and thus are affected.

But what is the actual issue?

fritshoogland's picture

Oracle database wait event ‘db file async I/O submit’ timing bug

This blogpost is a look into a bug in the wait interface that has been reported by me to Oracle a few times. I verified all versions from Oracle 11.2 version up to 18.2.0.0.180417 on Linux x86_64, in all these versions this bug is present. The bug is that the wait event ‘db file async I/O submit’ does not time anything when using ASM, only when using a filesystem, where this wait event essentially times the time the system call io_submit takes. All tests are done on Linux x86_64, Oracle Linux 7.4 with database and grid version 18.2.0.0.180417

So what?
You might have not seen this wait event before; that’s perfectly possible, because this wait event is unique to the database writer. So does this wait event matter?

fritshoogland's picture

A re-introduction to the vagrant-builder suite for database installation

In a blogpost introducing the vagrant builder suite I explained what the suite could do, and the principal use, to automate the installation of the Oracle database software and the creation of a database on a virtual machine using vagrant together with ansible and virtual box.

This blogpost shows how to use that suite for automating the installation of the Oracle database software and the creation of a database on a linux server directly, with only the use of ansible without vagrant and virtualbox.

martin.bach's picture

Hybrid Columnar Compression in 12.2 – nice new feature

Oracle 12.2 introduced an interesting optimisation for Hybrid Columnar Compression (HCC). Until 12.2 you had to use direct path inserts into HCC compressed segments for data to be actually compressed. If you didn’t use a direct path insert you would still succeed in entering data into the segment, however your newly inserted data was not HCC compressed. There is no error message or other warning telling you about that, which can lead to surprises for the unaware.

My friend and colleague Nick has pointed out that the official HCC white paper states – somewhat hidden – that this requirement is no longer as strict in 12.2. I haven’t managed to find the document Nick pointed out, but a quick search using my favourite retrieval engine unearthed the updated version for 18c.

fritshoogland's picture

A look into oracle redo, part 11: log writer worker processes

Starting from Oracle 12, in a default configured database, there are more log writer processes than the well known ‘LGWR’ process itself, which are the ‘LGnn’ processes:

$ ps -ef | grep test | grep lg
oracle   18048     1  0 12:50 ?        00:00:13 ora_lgwr_test
oracle   18052     1  0 12:50 ?        00:00:06 ora_lg00_test
oracle   18056     1  0 12:50 ?        00:00:00 ora_lg01_test

These are the log writer worker processes, for which the minimal amount is equal to the amount public redo strands. Worker processes are assigned to a group, and the group is assigned to a public redo strand. The amount of worker processes in the group is dependent on the undocumented parameter “_max_log_write_parallelism”, which is one by default.

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