Blog: Jonathan Lewis

209 blogs updated: 27 min. ago
Headline if you don't want to read the note the /*+ parallel(N) */ hint doesn't mean a query will use parallel execution, even if there are ...
25-05-2017 17:51:17 Jonathan Lewis Oracle
255 Again!
There's so many things that can go wrong when you start using tables with more than 255 columns here's one I discovered partly because I was...
23-05-2017 14:46:38 Jonathan Lewis Oracle
255 columns
This is one of my "black hole" articles I drafted it six months ago, but forgot to publish it. A recent post on OTN highlighted some of the ...
19-05-2017 18:55:29 Jonathan Lewis Oracle
Quantum Space
Here's a not very serious note that makes a serious point. I've got a small tablespace made up of 4 files, and here's a little report I can ...
10-05-2017 15:17:07 Jonathan Lewis Oracle
The opt_estimate hint is one of many that shouldn't be used in end-user code and isn't officially documented. Nevertheless like so many othe...
08-05-2017 09:20:10 Jonathan Lewis Oracle
Here's a performance problem that came up on OTN recently. The following query (reforematted) takes "ages" to run how do you address the pro...
02-05-2017 11:32:48 Jonathan Lewis Oracle
Imagine you're fairly new to Oracle and don't have a lot of background information at your fingertips; then one day someone tells you to rea...
01-05-2017 14:43:34 Jonathan Lewis Oracle
Quiz Night
If this is the closing section of a trace file from a single end-user session that has a performance problem, what's the most obvious deduct...
27-04-2017 19:21:18 Jonathan Lewis Oracle
Undo Understood
It's hard to understand all the ramifications of Oracle's undo handling, and it's not hard to find cases where the resulting effects are ver...
21-04-2017 12:43:45 Jonathan Lewis Oracle
Character selectivity
A recent OTN posting asked how the optimizer dealt with "like" predicates for character types quoting the DDL and a query that I had publish...
14-04-2017 14:52:40 Jonathan Lewis Oracle

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