Oracle 12c in-memory option and IO

This article is about the Oracle 12c in-memory option, and specifically looks at how the background worker processes do IO to populate the in-memory column store.

Hardware: Apple Macbook with VMWare Fusion 7.1.3.
Operating system: Oracle Linux 6.7, kernel: 3.8.13-118.el6uek.x86_64.
Database version: Oracle
Patch: opatch lspatches
19392604;OCW PATCH SET UPDATE : (19392604)
19303936;Database Patch Set Update : 12.1. (more...)

Direct path and buffered reads again: compressed tables.

In the previous post on the decision between buffered and direct path reads I showed the decision is depended on the version. Up to and including version the size of a segment needs to be five times small table threshold in order to be considered for direct path reads, and starting from the database starts considering direct path reads starting from small table threshold. The lower limit (more...)

Direct path and buffered reads again.

Since the direct path feature for serial processes was discovered after it became available in Oracle (as far as I know, I haven’t checked Oracle 11.1), there have been a lot of blog posts on when this happens. A lot of these do not specify the Oracle version, which is a failure in my opinion. There are different decisions made in different versions.

The purpose of this blogpost is to show (more...)

How the log writer and foreground processes work together on commit.

(warning: this is a rather detailed technical post on the internal working of the Oracle database’s commit interactions between the committing foreground processes and the log writer)

After the Trivadis Performance days I was chatting to Jonathan Lewis. I presented my Profiling the log writer and database writer presentation, in which I state the foreground (user/server) process looks at the commit SCN in order to determine if its logbuffer contents are written to disk by (more...)

Installing the Oracle database in docker

This blogpost is about how to install and run the Oracle database in docker. Please mind this is not an officially supported virtualisation platform for the Oracle database. This is a proof of concept setup.

Linux host setup.
In my setup, I used a linux host, freshly installed with Oracle Linux 6.7, which is going to be used as docker server. Please mind you need to leave diskspace (or a disk device) unused for (more...)

Oracle 12 and latches, part 2

In my previous post, I looked at non shared latches and how the latching is done by Oracle. This post is a description on how the latching works for shared latches.

The information is quite internal, if you landed on this page it might be a good idea to start with my first post on this topic: first post.

A famous example for shared latches is the ‘cache buffers chains’ latch.

For the sake (more...)

Oracle 12 and latches

Oracle DBAs who are so old that they remember the days before Oracle 11.2 probably remember the tuning efforts for latches. I can still recall the latch number for cache buffers chains from the top of my head: number 98. In the older days this was another number, 157.

But it seems latches have become less of a problem in the modern days of Oracle 11.2 and higher. Still, when I generate heavy (more...)

How long does a logical IO take?

This is a question that I played with for a long time. There have been statements on logical IO performance (“Logical IO is x times faster than Physical IO”), but nobody could answer the question what the actual logical IO time is. Of course you can see part of it in the system and session statistics (v$sysstat/v$sesstat), statistic name “session logical reads”. However, if you divide the number of logical reads by the total time (more...)

Investigating the full table direct path / buffered decision.

A lot of blogposts and other internet publications have been written on the full segment scan behaviour of a serial process starting from Oracle version 11gR2. This behaviour is the Oracle engine making a decision between scanning the blocks of a segment into the Oracle buffercache or scanning these blocks into the process’ private process global area (PGA). This decision is even more important on the Exadata platform, because the Oracle engine must have made (more...)

Hey dude, where’s my memory? part 2

In my previous article I started exploring the memory usage of a process on a recent linux kernel (2.6.39-400.243.1 (UEK2)), recent means “recent for the Enterprise Linux distributions” in this context, linux kernel developers would point out that the kernel itself is at version 3.19 (“stable version” at the time of writing of this blogpost).

The previous article showed that every process has its own address space, and that different (more...)