Blog: Jonathan Lewis


209 blogs updated: 27 min. ago
Parallelism
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 ...
6
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...
21
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 ...
23
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 ...
15
10-05-2017 15:17:07 Jonathan Lewis Oracle
opt_estimate
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...
23
08-05-2017 09:20:10 Jonathan Lewis Oracle
Aliases
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...
18
02-05-2017 11:32:48 Jonathan Lewis Oracle
RTFM
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...
14
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...
16
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...
30
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
14-04-2017 14:52:40 Jonathan Lewis Oracle


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