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Invisible ?
I’ll probably have to file this one under “Optimizer ignoring hints” – except that it should also go under “bugs”, and that’s one of the get-out clauses I use in my “hints are not hints” argument....
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12c Debug
Now that 12c is out, here’s an idea that might save you some time even if you have no intention of migrating to, or even testing, the product for a couple of years. Download the “List of bugs fixed in...
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12c subquery factoring
I’ve written a few notes about anomalies in subquery factoring (with subquery) in the past, principally making a fuss about the fact that moving an inline view into a “with subquery” can cause a plan...
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MV Refresh
Here’s a funny little problem I came across some time ago when setting up some materialized views. I have two tables, orders and order_lines, and I’ve set up materialized view logs for them that allow...
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Sorted Hash Clusters RIP
Sorted Hash Clusters have been around for several years, but I’ve not yet seen them being used, or even investigated in detail. This is a bit of a shame, really, because they seem to be engineered to...
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FBI decode
It probably won’t surprise many people to hear me say that the decode() function can be a bit of a nuisance; and I’ll bet that quite a lot of people have had trouble occasionally trying to get...
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Quiz Night
Okay, it’s a little early in the day (for me at least) to say “night” – but here’s a fun little detail I picked up in Prague yesterday. What do you think will happen when you try to execute the...
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Hash Clusters – 3
This note is a quick summary of an oddity that came to light after a twitter conversation with Christian Antognini yesterday. First a little test script to get things going: set serveroutput off define...
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Deferrable RI
Here’s a lovely little example that just came up on the OTN database forum of how things break when features collide. It’s a bug (I haven’t looked for the number) that seems to be fixed in 12.1.0.1....
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Not Pushing
Here’s an odd little optimizer glitch – probably irrelevant to most people, but an indication of the apparent randomness that appears as you combine features. I’ve created an example which is so tiny...
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Index Hash
I’m afraid this is one of my bad puns again – an example of the optimizer making a real hash of the index hash join. I’m going to create a table with several indexes (some of them rather similar to...
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Pagination
I was involved in a thread on Oracle-L recently started with the question: “How many LIOs is too many LIOs”. Rather than rewrite the whole story, I’ve supplied a list of links to the contributions I...
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12c join defect
This is a brief, temporary, note to draw attention to an item I wrote about 3 years ago demonstrating an anomaly with the plan Oracle could produce if the order of predicates in your where clause...
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12c subquery factoring
I’ve written a few notes about anomalies in subquery factoring (with subquery) in the past, principally making a fuss about the fact that moving an inline view into a “with subquery” can cause a plan...
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Index Compression – aargh
The problem with telling people that some feature of Oracle is a “good thing” is that some of those people will go ahead and use it; and if enough people use it some of them will discover a hitherto...
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FBI Skip Scan
A recent posting on the OTN database forum highlighted a bug (or defect, or limitation) in the way that the optimizer handles index skip scans with “function-based” indexes – it doesn’t do them. The...
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Predicate Order
Common internet question: does the order of predicates in the where clause make a difference. General answer: It shouldn’t, but sometimes it will thanks to defects in the optimizer. There’s a nicely...
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Empty Hash
A little while ago I highlighted a special case with the MINUS operator (that one of the commentators extended to include the INTERSECT operator) relating to the way the second subquery would take...
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Flashback Fail ?
Sitting in an airport, waiting for a plane, I decided to read a note (pdf) about Flashback data archive written by Beat Ramseier from Trivadis. I’d got about three quarters of the way through it when...
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Subquery Anomaly
Here’s an oddity that appeared on the OTN database forum last night: We have this query in our application which works fine in 9i but fails in 11gR2 (on Exadata) giving an “ORA-00937: not a...
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