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...)

Hey dude, where’s my memory?

This blogpost is about finding the actual amount of memory a process is taking. In order to do so, this post dives into the memory mechanisms of Linux. The examples in this article are taken from an Oracle Linux version 6.6 server, with kernel 2.6.39-400.243.1 (UEK2). This is written with the Oracle database processes in mind, but actually uses examples of a processes running ‘cat’, which means the contents of (more...)

Using the Oracle Grid Infrastructure Agents for GoldenGate on Oracle restart

I was testing Oracle Goldengate on a non-clustered Oracle database with ASM. With ASM, you need to have the grid infrastructure installed. The cluster ware for the single node install is called ‘oracle restart’.

The most convenient way to have Goldengate running at startup that I could find, was using the Oracle Grid Infrastructure Agents. These agents are not installed by default, you need to download these from the Oracle Technology (more...)

Oracle system V shared memory indicated deleted

This article is written with examples taken from an (virtualised) Oracle Linux 6u6 X86_64 operating system, and Oracle database version However, I think the same behaviour is true for Oracle 11 and 10 and earlier versions.

Probably most readers of this blog are aware that a “map” of mapped memory for a process exists for every process in /proc, in a pseudo file called “maps”. If I want to look (more...)

Quick diff for two pieces of text in vim

Sometimes you need to see the difference between two pieces of console output. When I research, this can be two stacktraces, but also /proc//maps and smaps output; really anything. Of course, there’s diff, but the diff output is not very visual. Also, diff doesn’t do diffing between more than two files.

This can be done reasonably simple in vim. Here’s how to do that:
1. start vi; vi
2. do a vertical split using a (more...)

Reading Oracle memory dumps

Every DBA working with the Oracle database must have seen memory dumps in tracefiles. It is present in ORA-600 (internal error) ORA-7445 (operating system error), system state dumps, process state dumps and a lot of other dumps.

This is how it looks likes:

Dump of memory from 0x00007F06BF9A9E00 to 0x00007F06BF9ADE00
7F06BF9A9E00 0000C215 0000001F 00000CC1 0401FFFF  [................]
7F06BF9A9E10 000032F3 00010003 00000002 442B0000  [.2............+D]
7F06BF9A9E20 2F415441 31323156 4F2F3230 4E494C4E  [ATA/V12102/ONLIN]
7F06BF9A9E30 474F4C45 6F72672F 315F7075  (more...)