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Thursday 30 June 2011

Vacation in Agioi Apostoloi, Kalamos

 In this new post a destination near to Athens will be briefly presented as an alternative to a daily excursion to the provinces of Attica; far away of the hectic life and the demonstrations of the busy city centre.
A view of the sea from the Panorama area

The place is called Kalamos,  its port Ag.Apostoloi  (the greek for Saint Apostles) and its distance from Athens centre is less than 50 Km, roughly an hour's journey by private car or public, fully air conditioned,  KTEL bus. You can find more about the geographical position here:
http://www.panoramio.com/photo/8841766 I think the images of the sea speak for themselves.

A view from Kalamos Beach hotel

As far as accommodation is  concerned,  there are two hotels  in the Agona area by the beach: the newer and therefore more expensive Delphinia (Greek for dolphins) and the older but cheaper Kalamos  Beach, which now mostly hosts tourists groups from Russia and the eastern Europe. There also are  plenty of rooms, or flats to let by  the seaside, in addition to whole houses for rent. Prices are as low as 270 euros per month for a 100 square meters house. Many German pensioners live in the Agona area all the year round.
During the winter, there might be so heavy snowfall that the landscape resembles that of the Swiss alps. That might happen once in  five years. In such case, no traffic is allowed due to bad weather, one must have made beforehand food, fuel provisions  to last for a period of a few days. Having a power generator in case of a power outage or some extra wood logs for the fireplace is always a good idea. I am sure the locals will be suitable to offer you advice or help during the winter season.

Landscape during winter

When the weather is good, besides swimming, fishing or chatting with the anglers, sailing, sunbathing and enjoying the clean sea, one could visit the woods, the vineyards to consult with the expert wine makers, go sightseeing to the nearby site of Amphiarion which once served as an oracle, the monasteries, Oropos town or the island of Evia and so on. Finally,  a word of caution: during the  hot weekends, especially on Sundays; it is very crowded, there is difficulty in driving a private car in such narrow streets. Thus, during the weekend getting the bus is the ideal suggestion, for trouble free amusement. It is fully recommended to visit this place during working week days, for having your share of carefree fun in the sun!

Further references:
http://www.athensguide.org/blog/2008/11/ktel.html

Friday 10 June 2011

Comments on EJB 3.0 Database Persistence with Oracle Fusion Middleware 11g, by Deepak Vohra

On the bright side, the text is well written,  providing a brief synopsis of the ejb 3, (not 3.01 which is the current) background and following a block by block explanation of each snippet of source code used. Apart from using the oracle db, the text presents an example of MySql db server and Eclipse too. The applications are usually tested and deployed to the Weblogic server version 10.1.x.x. g  via ant scripts.
On the dark side the source code consists of orphan files, neither ears, nor whole JDeveloper workspaces; as it is usual in oracle university courses solutions. Moreover, the code seems to be what is printed in the text and has some errors. For example: in chapter 2, on page 33 the  modified ejb-jar.xml deployment descriptor reads like this:

<ejb-ql>
<![CDATA[SELECT OBJECT(a) FROM CatalogBean AS a WHERE a.catalogId = ?1
</ejb-ql>

meaning that the <![CDATA[ tag is not closed properly, as it is easily understood when these lines are pasted to the editor window. In chapter 4,in CatalogTestSessionEJBBean the method is not persistEntity(catalog), but persistCatalog(catalog) and so on. After some investigation or debugging, one persistent reader will probably end up with a working application.  A mistake which occurs numerous times is the number 2 missing from any sql statement with a VARCHAR2 datatype.  Therefore, it seems that gathering the source code of the book was maybe only an afterthought.  Furthermore, some screenshots and relevant text instructions, apply only to older versions of JDeveloper, other than the current 11.1.2. More advanced topics such as tuning, are beyond the scope of this book.

All in all, the text could be a valuable introduction to combining ejb 3 and fusion for JDeveloper funs. This is recommended for zealots of ADF business components, in order to compare both model tier technologies, especially performance. As it was written back in 2010, ejb technology has somehow superceded it. Thus, if you are a Netbeans fun, you will probably think that is an obsolete book. However, the current JDeveloper version does not seem to support ejb 3.01, so to loyal JDevepoper fanatics, it won't make any difference at all!

Monday 30 May 2011

Comments on Oracle Performance Survival Guide: A Systematic Approach to Database Optimization, by Guy Harrison

On the bright side, this is one of the easiest review for me to write, since there are so many readers of the several editions of the book, that I shall mainly copy and paste  some lines of reviews I agree to. Thus, I quote: " This book is an encyclopedic overview of all aspects of Oracle performance. Mr. Harrison takes a layered approach, starting at the top with application and data model design where the focus is minimizing the demand for database resources. He then moves down into database code internals, where the focus is maximizing concurrency through reduction of lock, latch, and mutex contention. The next step is to optimize memory usage to minimize the need for physical IO. Finally, he moves to the bottom layer, where the focus is on optimizing physical IO at the disk layer.

Each of these layers is worthy of its own book, so to combine all these topics in a single book is an ambitious goal. Indeed, experienced readers will often want a bit more detail, or wonder why their favorite optimization was not mentioned. However, Mr. Harrison strikes a very good balance between depth and coverage. He also provides a very useful bibliography, including the Oracle documentation, books, and Internet sites and blogs.


For each chapter, Mr. Harrison provides extraordinarily clear, concise, and helpful introductions and summaries. He also uses boxed borders to highlights particularly important points within the text. One can learn a great deal by simply reading these summaries and boxed items, and these can also be used to help the reader find relevant sections, which is especially valuable in a book of this length.


This book is not the last word on SQL tuning, optimizer internals, Oracle troubleshooting, the SGA, nor latch contention. However, its coherent approach, useful summaries and highlights, and efficient organization, make it a valuable and essential guide to anyone wishing to expand their Oracle performance skill set.


The target audience includes both application developers and DBAs. It covers 10g, 11g, 11gR2, with context from 8i and 9i ."
The latter is true for the newest edition of course! Furthermore, the full source code is available, as well as an errata page on the author's site.

On the dark side, there are extensive sections of the text promoting the products Mr. Harrison and his company create, which although humorously introduced ("Full disclosure..."), are a waste of time to read, for open source funs or anyone who is not interested in buying the software.

All in all, the book is highly recommended and I am looking forward to reading each new edition. Congratulations to the author. Well done, indeed!