Blog: Jonathan Lewis

209 blogs updated: 54 min. ago
Question Time
It's that time of year again the UKOUG Tech conference is approaching and I've organised a panel session on the Cost Based Optimizer. This y...
19-10-2017 21:34:33 Jonathan Lewis Oracle
In memoriam – 3
My father-in-law died a few weeks ago, aged 95. This is the story that he wrote for his children and grandchildren a few years ago describin...
11-10-2017 15:15:02 Jonathan Lewis Oracle
12c Parse
Following on from a comment to a recent posting of mine about "bad" SQL ending up in the shared pool and the specific detail that too much b...
06-10-2017 10:13:02 Jonathan Lewis Oracle
Here's a quick quiz. According to the Oracle 12.1 Database SQL Tuning Guide the first stage of parsing a statement is the Syntax Check, whic...
03-10-2017 18:14:15 Jonathan Lewis Oracle
How can a single piece of SQL text checked very carefully end up with multiple SQL_IDs ? There are probably quite a lot of people who know t...
02-10-2017 10:31:55 Jonathan Lewis Oracle
With Subquery()
Here's a little oddity that came up recently on the OTN database forum an example where a "with" subquery (common table expression / factore...
19-09-2017 21:31:20 Jonathan Lewis Oracle
Join Elimination Bug
A few years ago a bug relating to join elimination showed up in a comment to a post I'd done about the need to keep on testing and learining...
14-08-2017 13:52:56 Jonathan Lewis Oracle
Rebuilding Indexes
One of the special events that can make it necessary to rebuild an index is the case of the "massive DML", typically a bulk delete that purg...
03-08-2017 14:54:07 Jonathan Lewis Oracle
Redo OP Codes:
This posting was prompted by a tweet from Kamil Stawiarski in response to a question about how he'd discovered the meaning of Redo Op Codes ...
25-07-2017 19:47:21 Jonathan Lewis Oracle
Fast Now, Fast Later
The following is the text of an article I published in the UKOUG magazine several years ago (2010), but I came across it recently while writ...
24-07-2017 14:49:49 Jonathan Lewis Oracle

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