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inmemory area is another sub-heap of the top-level SGA heap

I blogged earlier about heap dump shared pool heap duration and was curious to see how the inmemory – new feature – is implemented. This is a short blog entry to discuss the inmemory area heap.


I have set the initialization parameters sga_target=32G and inmemory_size=16G, meaning, out of 32GB SGA, 16GB will be allocated to inmemory area and the remaining 16GB will be allocated to the traditional areas such as buffer_cache, shared_pool etc. I was expecting v$sgastat view to show the memory allocated for inmemory area, unfortunately, there are no rows marked for inmemory area (Command “show sga” shows the inmemory area though). However, dumping heapdump at level 2 shows that the inmemory area is defined as a sub-heap of the top level SGA heap. Following are the commands to take an heap dump.

EM Cloud Control 12c : The 24 Hour DBA

I think I’ve lived through all the ages of Enterprise Manager. I used the Java console version back in the days when admitting you used it got you excommunicated from the church of DBA. I lived through the difficult birth of the web-based Grid Control. I’ve been there since the start of Cloud Control. I’ll no doubt be there when it is renamed to Big Data Cloud Pixie Dust Manager (As A Service).

I was walking from the pool to work this morning, checking my emails on my phone and it struck me (not for the first time) that I’m pretty much a 24 hour DBA these days. I’m not paid to be on call, I’m just a 9-5 guy, but all my Cloud Control notifications come through to my phone and tablet. I know when backups have completed (or failed). I know when a Tnsping takes too long. I know when we have storage issues. I know all this because Cloud Control tells me.


So is out with a number of interesting new features, of which the most noisily touted is the “in-memory columnar storage” feature. As ever the key to making best use of a feature is to have an intuitive grasp of what it gives you, and it’s often the case that a good analogy helps you reach that level of understanding; so here’s the first thought I had about the feature during one of the briefing days run by Maria Colgan.

“In-memory columnar storage gives you bitmap indexes on OLTP systems without the usual disastrous locking side effects.” Released With Cool Indexing Features (Short Memory)

Oracle Database has finally been released and it has a number of really exciting goodies from an indexing perspective which include: Database In-Memory Option, which enables specific portions of the database to be in dual format, in both the existing row based format and additionally into an efficient memory only columnar based format. This in […]

Invoker Rights in Oracle Database 12c : Some more articles

I wrote about the Code Based Access Control (CBAC) stuff in Oracle Database 12c a while back.

I’ve recently “completed the set” by looking at the INHERIT PRIVILEGES and BEQUEATH CURRENT_USER stuff for PL/SQL code and views respectively.

12c Index Like Table Statistics Collection (Wearing The Inside Out)

This change introduced in 12c has caught me out on a number of occasions. If you were to create a new table: And then populate it with a conventional insert: We find there are no statistics associated with the table until we explicitly collect them: But if we were to now create an index on this […]

Data visualization, px qref waits, and a kernel bug!

Data visualization is a useful method to identify performance patterns. In most cases, I pull custom performance metrics from AWR repository and use tableau to visualize the data. Of course, you can do the visualization using excel spreadsheet too.

Problem definition
We had huge amount of PX qref waits in a database:

Automatic Diagnostics Repository (ADR) in Oracle Database 12c

There’s a neat little change to the Automatic Diagnostics Repository (ADR) in Oracle 12c. You can now track DDL operations and some of the messages that would have formerly gone to the alert log and trace files are now written to the debug log. This should thin out some of the crap from the alert log hopefully. Not surprisingly, ADRCI has had a minor tweak so you can report this stuff.

You can see what I wrote about it here:

Of course, the day-to-day usage remains the same, as discussed here:



Subquery with OR

Prompted by a pingback on this post, followed in very short order by a related question (with a most gratifying result) on Oracle-L, I decided to write up a note about another little optimizer enhancement that appeared in 12c. Here’s a query that differs slightly from the query in the original article:

Extended stats

Like the recent article on deleting histograms this is another draft that I rediscovered while searching for some notes I had written on a different topic – so I’ve finally finished it off and published it.

Here’s a quirky little detail of extended stats that came up in an OTN thread earlier on this week [ed: actually 8th Jan 2014]. When you create column group stats, Oracle uses an undocumented function sys_op_combined_hash() to create a hash value, and if you gather simple stats on the column (i.e. no histogram) you can get some idea of the range of values that Oracle generates through the hash function. For example: