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August 2008

Flexible sampling of any V$ or X$ view with sample.sql

In recent past I’ve blogged few scripts which use specially crafted ordered nested loop for sampling contents of V$ and X$ views fast, with plain SQL.

If you haven’t read them yet, here are the links:

I wrote the above scripts having special purposes in mind (e.g. profile session waits or latching activity).

Flexible sampling of any V$ or X$ view with sample.sql

In recent past I’ve blogged few scripts which use specially crafted ordered nested loop for sampling contents of V$ and X$ views fast, with plain SQL.

If you haven’t read them yet, here are the links:

I wrote the above scripts having special purposes in mind (e.g. profile session waits or latching activity).

Partition-wise dependencies in 10g release 2

Modify partitions without invalidating dependant objects. October 2007 (updated August 2008)

AWR Usage Poll

A number of recent threads in the Oracle-L list have made it pretty clear that Automated Workload Repository (AWR) is a tool that you are expected to use when troubleshooting a database problem.

Never mind the fact that AWR is still a product that is licensed separately from the database, and that a large segment of the Oracle DBA population doesn't seem to realize that. Or that Active Session History (ASH) is part of AWR, and falls under the same license restrictions.

So I conducted a poll regarding the use of AWR. AWR Usage Poll. If you haven't in the AWR Poll, please do so.

While the web site does provide a chart of results, those results don't include the extra comments made by poll takers. You may are may not be able to download all the results, I'm not sure if that is restricted to the poll owner.

Case study on some rowcache internals, cached non-existent objects and a describe bug

I got a question regarding Metalink note 296235.1 about a describe bug which causes objects to “disappear” when they are described when database is not open.
It was an interesting case involving a bug, so I wrote a quite long analysis with test cases today. However when posting the entry to wordpress, it managed to completely mess up the formatting. After wasting half an hour trying to get the formatting correct I gave up and saved the article into a PDF instead.

Case study on some rowcache internals, cached non-existent objects and a describe bug

I got a question regarding Metalink note 296235.1 about a describe bug which causes objects to “disappear” when they are described when database is not open.
It was an interesting case involving a bug, so I wrote a quite long analysis with test cases today. However when posting the entry to wordpress, it managed to completely mess up the formatting. After wasting half an hour trying to get the formatting correct I gave up and saved the article into a PDF instead.

Why does even a small difference in SQL text cause a hard parse?

I just replied to an Oracle Forum Thread about why does even a small difference in SQL statement text cause it to be hard parsed and loaded as a different cursor. The reason is actually very simple – and I’m posting it into my blog too:

 The reason why a statement with even a minor difference in text is parsed as a separate cursor is due how Oracle looks up statements from library cache.

Why does even a small difference in SQL text cause a hard parse?

I just replied to an Oracle Forum Thread about why does even a small difference in SQL statement text cause it to be hard parsed and loaded as a different cursor. The reason is actually very simple – and I’m posting it into my blog too:

 The reason why a statement with even a minor difference in text is parsed as a separate cursor is due how Oracle looks up statements from library cache.

Script: Display valid values for multioption parameters (including hidden parameters)

I wrote a little script pvalid.sql for listing valid values for multioption parameters (the ones which are not string, number or boolean type, but accept a parameter from predetermined list, like optimizer_mode which can have values of ALL_ROWS, FIRST_ROWS, CHOOSE, FIRST_ROWS_1, etc).

The script accepts a (part of) Oracle parameter name as first argument, for example the following output is from Oracle 10.2.0.3 database:

Script: Display valid values for multioption parameters (including hidden parameters)

I wrote a little script pvalid.sql for listing valid values for multioption parameters (the ones which are not string, number or boolean type, but accept a parameter from predetermined list, like optimizer_mode which can have values of ALL_ROWS, FIRST_ROWS, CHOOSE, FIRST_ROWS_1, etc).

The script accepts a (part of) Oracle parameter name as first argument, for example the following output is from Oracle 10.2.0.3 database: