22. Nov. 2008

Working with Oracle, using TEMPORARY tablespaces with tempfiles is best practice today. Unfortunately there are two situations in which you may encounter trouble as for the tempfiles are missing and sort operations do no longer succeed.

Curiously and based on the fact that Oracle does not record checkpoint information in tempfiles, Oracle can even start up a database with a missing tempfile.

DBW0 will write to a trace file indicating the tempfile is not found, but the database opens normally and later on only sort operations will fail with some of the Oracle Errors ORA-01116, ORA-01157 and ORA-25153.

Such situation can be caused by simply the OS file related to a tempfile cannot be not found anymore or the logical tempfiles attached to the TEMPORARY tablespace do not exist anymore.

This can happen in case the tempfile was located on a disk that crashed, had a bad controller, or some other type of media failure, a recovery or cloning of the database was done before and/or finally and purely caused by human error.

Solution : Drop the logical tempfile and add a new one

SQL> alter database tempfile ‘/oracle/oradata/SID/tempfile.tmp’ drop;

Database altered.

SQL> select tablespace_name, file_name from dba_temp_files;

no rows selected.

SQL> alter tablespace temp add tempfile ‘/oracle/oradata/SID/tempfile.tmp’ size 100m;

Tablespace altered.

21. Nov. 2008

When transferring data from one server to another – maybe for backup reason – most people use tar to create an archive. Then they copy it to the new server and untar it or leave it as a tarfile as backup.

Working with UNIX and using a trick  you can transfer it with compression and speed up the whole transfer time a lot.

Using the output result of  a command directly as the command line input of a second command  using a  Unix Pipe the need of writing it down to disk first no longer exists. Finally accessing the remote system though a ssh tunnel will even transfer the compressed data over the network within one single step.

Invoking the following single command will transfer all your data within sourcedirectory an Server B and immediately store it locally  on Server B within a compress archive:

ssh username@hostname "cd /sourcedirectory/ ; tar czf – ." > /targetdirectory/filename.tgz

While the following variation:

ssh username@hostname "cd /sourcedirectory/ ; tar czf – ."> /targetdirectory/filename.tgz| tar xvf –

will directly extract it again for you on the your local system.

20. Nov. 2008

As a Web Developer we sooner or later maybe required to work with a CMS (Content Management System), perhaps out of own interest or plainly being forced by a customer request.

The idea behind such tools is the try to separate the data from the presentation layer. Following this approach later on it will be easy to change the look and feel of your site just by changing or updating the template used, immediately all content pages will get shown in that brand new look without changing them one by one.

Setting up such a CMS is fairly easy, first by uploading all files that come with it to your server. We now need to put together your database details as they are the key to your central data store and specifying them together with a few other essential (but usually not difficult to answer) questions during a typical setup procedure. From then on it is just learning about and working with the tool ├▒specify what tool, is it CMS(?) – to get your site ready to use.

Your site, usually developed on your own server, or within a subfolder of the original environment sooner or later you may find the need to move your installation.

In all cases the principle process is the same. Following the idea of a CMS, data can be either located within the file system, the database, or within both. So moving a CMS always requires moving both!

We have already given you a few tips here about how to move the files between servers quickly and therefore we will now focus on the database data only.

The main benefit of a database is that the data is stored within, in a very efficient way for accessing it quickly and in a structured way. Most databases come with some binary data export/import tools for transferring both data and structures.

Making a WordPress move and the usual MySQL database, phpMyAdmin is the tool of our choice. Mostly offered by the hosting provider itself it is often part of your hosting package and easy to access.

Once started it offers you a nice and neat surface interface enabling you to work with your database and it hopefully will not take you long to get familiar with it. With the main view opened and looking at your database the menu directly offers you the options export and import. Now choosing export we usually can go on with the offered defaults. But to prevent problems I would recommend you to ensure that the check boxes "Add DROP TABLE" and "Complete inserts" are checked and "Export type" is defined as "INSERT".

With this set we can now press "Go" and the result will be a long and curious screen output containing both, the data and all necessary SQL (Structured Query Language) elements, later on it is necessary to re-import this data.

This output we will now cut & paste to an ASCII Editor of our choice and the reason for this is there maybe references pointing to structures of the old server we now have to change (now hopefully making them "relative"). Within the editor this can be done easily by using the usual search and replace function.

Importing the data back into the database or transferring it to another one, we now copy & paste our content back into phpMyAdmin and connect to the new target database. For the re-import I recommend the SQL functionality of the tool. There you can just paste your script into the big SQL input field and finally press the OK button below. And after a few seconds of processing, a friendly message will tell us that our data is stored back within the database.

Having ported both – data and files – we finally need to change a few runtime settings of the WordPress installation.

Once again you should be aware that we are working with two different locations; database and filesystem and you will understand tweaks will be required to both.

All the necessary information to access the database is stored within a file wp-config.php. We should remember that file as it was part of the initial installation we did earlier.

Now we open this configuration file within an editor of our choice and replace the relevant parts e.q. username, password, database, server and table prefix with the correct new values.

Finally and as a last step we have to head back to the phpMyAdmin and navigate down to a table called  wp_options. Browsing the content of this table we will see two option rows siteurl (option_id=1) and home (option_id=39) which contains the old site URL as an argument. Adjusting them with the new site URL will finally allow us to run the WordPress on our new Server without issues.

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