Who's online

There are currently 0 users and 28 guests online.

Recent comments


Oracle database operating system memory allocation management for PGA – part 2: Oracle 11.2

This is the second part of a series of blogpost on Oracle database PGA usage. See the first part here. The first part described SGA and PGA usage, their distinction (SGA being static, PGA being variable), the problem (no limitation for PGA allocations outside of sort, hash and bitmap memory), a resolution for Oracle 12 (PGA_AGGREGATE_LIMIT), and some specifics about that (it doesn’t look like a very hard limit).

But this leaves out Oracle version 11.2. In reality, the vast majority of the database that I deal with at the time of writing is at version 11.2, and my guess is that this is not just the databases I deal with, but a general tendency. This could change in the coming time with the desupport of Oracle 11.2, however I suspect the installed base of Oracle version 12 to increase gradually and smoothly instead of in a big bang.

Oracle database operating system memory allocation management for PGA

This post is about memory management on the operating system level of an Oracle database. The first question that might pop in your head is: isn’t this a solved problem? The answer is: yes, if you use Oracle’s AMM (Automatic Memory Management) feature, which let’s you set a limit for the Oracle datababase’s two main memory area’s: SGA and PGA. But in my opinion any serious, real life, usage of an Oracle database on Linux will be (severely) constrained in performance because of the lack of huge pages with AMM, and I personally witnessed very strange behaviour and process deaths with the AMM feature and high demand for memory.

UKOUG Tech14 slides – Exadata Security Best Practices

I think 2 years is long enough to wait between posts!

Today I delivered a session about Oracle Exadata Database Machine Best Practices and promised to post the slides for it (though no one asked about them :). I’ve also posted them to the Tech14 agenda as well.

Direct download: UKOUG Tech14 Exadata Security slides Introduction to Zone Maps Part II (Changes)

In Part I, I discussed how Zone Maps are new index like structures, similar to Exadata Storage Indexes, that enables the “pruning” of disk blocks during accesses of the table by storing the min and max values of selected columns for each “zone” of a table. A Zone being a range of contiguous (8M) blocks. I […]

Oaktable World 2014 Jonathan Lewis: Breaking Exadata

See video

Exadata and Virtual Private Database: will it offload my query?

During one of the classes I taught about Exadata optimisations I had an interesting question:

If I am using VPD, will Exadata still offload the query?

Background is that we discussed function offloading, and the meta-view v$sqlfn_metadata. It turned out that SYS_CONTEXT() is not offloadable in

About index range scans, disk re-reads and how your new car can go 600 miles per hour!

Despite the title, this is actually a technical post about Oracle, disk I/O and Exadata & Oracle In-Memory Database Option performance. Read on :)

If a car dealer tells you that this fancy new car on display goes 10 times (or 100 or 1000) faster than any of your previous ones, then either the salesman is lying or this new car is doing something radically different from all the old ones. You don’t just get orders of magnitude performance improvements by making small changes.

Perhaps the car bends space around it instead of moving – or perhaps it has a jet engine built on it (like the one below :-) :

Intra-Database IORM in action

I have been teaching the Enkitec Exadata Administration Class this week and made an interesting observation I thought was worth sharing with regards to IO Resource Management on Exadata.

I have created a Database Resource Manager (DBRM) Plan that specifically puts a resource consumer group to a disadvantage. Actually, quite severely so but the following shouldn’t be a realistic example in the first place: I wanted to prove a point. Hang-on I hear you say: you created a DBRM plan-the post has IORM in the subject though: what gives? Please allow me to explain.

Exadata offers 3 different ways to implement IORM to the keen engineer:

Oracle IO wait events: db file sequential read

(the details are investigated and specific to Oracle’s database implementation on Linux x86_64)

Exadata IO: This event is not used with Exadata storage, ‘cell single block physical read’ is used instead.
p1: file#
p2: block#
p3: blocks

Despite p3 listing the number of blocks, I haven’t seen a db file sequential read event that read more than one block ever. Of course this could change in a newer release.