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Michael McLaughlin's Old Technical Blog

Oracle networking – some ugly duckings

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I tried to answer a question in the forum a couple weeks ago about connections. It contained all the trite stuff about check this, then that, et cetera because I couldn’t remember why I’d seen an TNS-03505 error. It returns an illustrative message “Failed to resolve name” error. Along the way, I tripped into ORA-12560 and one I’d never seen before an ORA-12518. If you want the dirt on these read on …

You’ll typically encounter this error when you’re working on a laptop. It gets triggered when you run the tnsping utility. When you’ve qualified the hostname and hostname.domain name in the hosts file and in the tnsnames.ora file, it’ll throw the TNS-03505 error because you’re on another network. You may also encounter it when there’s a change or discrepancy between the machine hostname and DNS server results. Lastly, you may encounter it when you’ve lost the lease on an IP address and now have a new lease with a different IP address.

These errors effectively block successful tnsping calls. You get around it by shutting down the listener, modifying the IP address in the tnsnames.ora file if you’re not using a hostname, setting the %TNS_ADMIN% environment variable in a command session when you have multiple Oracle homes, and restarting the listener.

This is the sqlplus utility cousin of the TNS-03505. All the rules that apply to it apply to this.

This one is cute. I only hit it because my touchpad is too sensitive on the Dell laptop. It occurs if you pause the Windows listener service. You fix it by restarting the service. It is an enigma within a conundrum (Churchill on the old Soviet Union) why anybody would create a service like this with a pause option. Wouldn’t it be cool if somebody at Oracle were listening now (that is reading this blog) and they got the service fixed.


Written by maclochlainn

October 24, 2008 at 4:18 pm

Posted in Oracle

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AJAX gone wrong, or the dynamic duo Blackboard & IE

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We’ve got an implementation of Blackboard running on Oracle 10g. The new version has a grade book redesign that uses AJAX to eliminate the cumbersome nature of its predecessor. It was interesting figuring out why grades entered wouldn’t show without restarting Internet Explorer, while Firefox and Safari worked fine. Another heart found thank you to Microsoft for failing to optimize JavaScript execution in their browser (all the way through to 8). Read on if you must use IE.

The issue is that Internet Explorer reads JavaScript including all whitespace at initial page load. There’s no attempt to compress it, arghhh. Naturally, that makes performance crawl a bit on initial page load. That wouldn’t be bad but Blackboard’s JavaScript changes DOM values during product use. Those changes go unseen if you navigate from the Grade Book and return to it. At least, they do when you’re using default IE settings. Unlike Microsoft’s solution to the problem of suppressing Mac purchases (an advertising gem from Apple), Microsoft didn’t spend more on marketing (after all the Windows platform is more or less captured by IE). They simply set the default value for page refreshes to automatic, which means once per active IE load into memory for JavaScript files. Then, it is Blackboard’s fault for how it implemented AJAX, right?

You can fix this default by taking one step. Open IE, navigate to Tools, Internet Options, and then click the Settings button in the Browsing history section. The form looks like:

When you click on the Settings button, you’ll come to the following screen. Click the radio button for “Every time I visit the webpage,” which will ensure you get a working grade book in Blackboard.

Click the OK button. You’re not done yet. You must shut down all IE sessions and re-launch the product for the changes to occur. If you think that was tedious, here we need to do it every time our corporate governance folks push an update to Windows because they reset IE to an incompatible set of values for Blackboard’s AJAX implementation.

Written by maclochlainn

October 23, 2008 at 9:16 pm

Inline views, table fabrication, and the WITH clause

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Sometimes working with a product like Oracle brings a surprise, like a new feature you failed to catch when it was released. I’ve seen a lot of entries using inline views through the WITH clause in the Oracle forums. It caught my eye because it is such a radical departure from portable SQL syntax of an inline view. I finally went searching to find the rationale for this approach.

The answer doesn’t lie with the Charlotte like National Treasure, but with simplifying the join syntax, as qualified in the Oracle Database 2 Day + Data Warehousing Guide 11g, Release 1. The following looks at this approach, and compares using the WITH clause instead of the inline view to perform table fabrication.

Oracle tells us to use the WITH clause when a query has multiple references to the same query block and there are joins and aggregations. Basically, the WITH clause lets you name inline views and then reuse them inside other inline views. Like PL/SQL, they must be defined before they can be referenced. Unlike PL/SQL, they have no equivalent for forward referencing a query block. The basic syntax is:

The first code block is assigned the inline name. You can then reuse the inline code block inside any subsequent code block or the master query. The idea is that this syntax is simpler than the generic syntax.

The standard way of writing this is consistent across other SQL databases, and I don’t really see it as any more complex than the WITH syntax Oracle provides.

The WITH clause is also capable of letting you create tables from literal values, which is known as table fabrication. The following syntax uses the with clause to fabricate a table of two columns (x and y) and two rows.

The next shows the traditional way of fabricating a table using an inline view:

You can also use this type of syntax in MySQL to fabricate a table. You can’t use the WITH clause in MySQL because it’s not supported. You’ll notice in the example that the FROM dual portion is omitted in MySQL. Wouldn’t it be nice if Oracle let that happen too?

A neat function that I picked up on the Oracle Technical Network is the NUMTODSINTERVAL (number to date-stamp interval) function, which can create intervals for qualifying sales by hour or quarter hour. More or less it is a way to fabricate timing intervals. Here’s a quick example:

This has been the syntax, now I’ll have to check whether there are any performance differences. I suspect that since the execution plan is the same that there aren’t any performance differences but you never know until you test it.

Written by maclochlainn

October 19, 2008 at 6:45 am

Reflecting on six months of blogg’n

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It is nice to know that the entries I’ve made have readers. It’s surprising to see almost 22,000 direct hits and another 5,000 syndicated hits in the 6 months of blogg’n. The following table contains the list and links of the top blogs that have netted 5 or more hits per day.

Blog Entry Posted Hits Avg
How to configure Mac OS X as an Oracle Client 9/2/2008 1,402 36
How to convert XML to CSV and upload into Oracle 6/22/2008 1,019 9
Creating an external table that uses SQL*Loader 6/19/2008 945 8
Creating an external table that uses Oracle Data Pump 6/19/2008 899 8
Pipelined functions and PL/SQL Tables 5/11/2008 859 5
Reading an external directory from SQL or PL/SQL 6/05/2008 667 5

I plan to move this to my own site shortly and will provide notice and pay WordPress to forward. Naturally, any comments are welcome.

Written by maclochlainn

October 17, 2008 at 11:05 pm

Posted in Generic

Setting up a printer in VMWare Ubuntu instance

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As I mentioned before, working in the virtual machine is a great solution when you need to work in multiple operating systems. Setting up printing is a step that goes with the operating system. It is very easy to configure in Ubuntu running in VMWare on a Mac OS X machine.

I found that the standard printer in the virtual machine wouldn’t work. I tried it in both VMWare 1.x and 2.x but without any luck. It did work ineffectively in VMWare 2.x but it embedded characters in simple documents that shouldn’t be there. Finally, I pursued this course. It has the benefit of working like you’d expect! It lets you print your native Ubuntu documents when you’ve configured the VMWare machine in NAT or bridged networking mode. The only difference is that a bridged network doesn’t require you to share the printer on the Mac OS because it directly accesses it.

The first step using a NAT network requires that you share you printer setup on the Mac OS. You do that by launching System Preferences, then click on Sharing. In Sharing, you enable print sharing by chosing the network printer …

After you’ve enabled sharing on the Mac OS, you can take the following steps in Ubuntu:

1. Click the System menu choice, choose Administration. and Printing, as shown in screen shot:

2. You’ll then see the following screen but not gray scaled. If you don’t, you’ll also see the following form. a gray scaled version indicates that you’ve run VMWare Tools before updating the Ubuntu OS CUPS service:

As mentioned, this means there’s a problem with a disabled service – typically cups (Common Unix Printing Service). You can click the Help, then Troubleshoot to further diagnose the problem. In the first screen click the Forward button to continue. In this screen, click the Not Listed (because it should be an empty list), and then click the Forward button to continue. You most likely will see the following dialog box, which tells you that the cups service is stopped (a general occurrence when you upgrade from VMWare Fusion 1.x to 2.x).

There’s a temptation to follow the instructions, and I yielded to it without a positive outcome. What you’ll find is that the cups (cupsys) service is enabled but if you use the VMWare Fusion menu, you’ll find that it isn’t, as shown:

If you stop here and check in a terminal session, you’ll see that life isn’t rosy after the upgrade. Even if you check it and restart the VM, the printing problem won’t resolve. This appears to be a part of the recompilation of cups by the VMWare Tools. It appears to happen when you opt to compile Ubuntu CUPS while running the VMWare Tools. You’re only prompted to compile these if you’re not on the most current CUPS release by Ubuntu.

You use the following command to check the status of the printer service:

# sudo /etc/init.d/cupsys status

You will most likely get something like this if you have a problem:

Status of Common Unix Printing System: cupsd is not running but /var/run/cups/ exists.

This is where it becomes obvious that the VMWare Fusion 2.x upgrade can introduce the problem. It is simple to avoid the problem by ensuring that the Ubuntu OS is patched to the most current CUPs version before running the VMWare Tools. I fixed the problem by reinstalling Ubuntu from scratch, and patching it to the current level. Then, you won’t have a failure of the CUPS process.

When you fix any errors from the upgrade or provided you’re on VMWare Fusion 2.x, you should click the Show printers shared by other systems check box, then click the Refresh button to display any network printers if they don’t refresh automatically.

3. You click on the desired network printer, which displays the following screen. Click the Make Default button after you click the Print Test Page button.

If you caught my post on doing this in a Microsoft Windows environment, isn’t it stuning how easy Ubuntu is compared to the “user-friendly” Windows interface (unless you’re upgrading). If you need the Windows instructions, you can find them here.

Reference Cursors – Why, when, and how?

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Quick Update: I move the blog because folks told me the screen shots weren’t as useful as copiable and formatted code. You can find both and new content in the updated blog posting here, I apologize for the inconvenience but there wasn’t a way to redirect you from WordPress.

A week or two ago, I noticed a discussion on the Oracle Technical Network forum that asked some questions about reference cursors. The discussion made me reflect if there were a couple simple rules for using reference cursors. This contains my take on the rules and some examples.

What are they …
There are two types of reference cursors. They are either weakly or strongly typed PL/SQL only data types. A weakly typed cursor doesn’t anchor the output of a query to a table or view, and implements the PL/SQL SYS_REFCURSOR type. A strongly typed cursor anchors the output of a query to a table or view, and typically anchors itself to a package or local user defined type (UDT) of a cursor.

They’re defined in the declaration block or a package specification, like this:

TYPE weak_cursor IS REF CURSOR;
TYPE strong_cursor IS REF CURSOR RETURN table_name%ROWTYPE;

When you opt to use a weakly typed cursor, you can anchor it to a PL/SQL structure that is a collection of a PL/SQL record structure. This is known as an associative array, and commonly called a PL/SQL table. However, it seems politically insensitive to use that language even though Oracle published it as such in the Oracle 8 documentation because it isn’t really a table but an implementation of a list of record structures. That means the index is sparsely populated or may contain breaks in a numeric index sequence. You can also use character string indexes from Oracle 10g forward to index this type of collection.

Why should you use them …
They’re useful structures when you want to open a cursor with known output columns in one program unit and move it to another for processing. Strongly typed reference cursors are appropriate for this purpose when both the passing and calling program units are in PL/SQL. Weakly typed reference cursors can also be used passing and calling PL/SQL programs. Weakly typed reference cursors require the same structures as strong reference cursors. Specifically, you will need a record structure for row-by-row fetch and collection of a record structure for bulk fetch. Whether you define them as strong or weak, you’ll need these structures for use inside PL/SQL program units that read the cursor. As a rule of thumb, you should generally define them as strongly typed reference cursors when they’re used exclusively in PL/SQL.

The most effective use of weakly typed reference cursors is in external OCI programming languages. Actually, it appears that weakly typed cursors have little use anywhere but in an OCI program. In external programming languages, you can fetch associations and dynamically discover the structure of a weakly typed reference cursor. That’s why they’re useful in OCI programming languages. You can find an example of using a weakly typed cursor in a PHP program on this blog entry.

How you use them …
You can find an example of using a weakly typed reference cursor as an input parameter in this discussion of pipelined PL/SQL functions. You can return a weakly typed cursor from an NDS (Native Dynamic SQL) statement as follows:

Outside of an OCI program, the only way to query this is with a SQL statement like:

You can return and query a weakly typed cursor as a strongly typed cursor by doing four things. Anchor the cursor statement to a table or view in the database catalog. Create a record structure to store rows of the reference cursor in an ordinary fetch, or a record structure and associative array collection data type to store a set of rows of the reference cursor. Then, explicitly open the reference cursor into the variable. Here is the detail to support those steps:

1. Create a package specification, that acts like an Object-oriented interface because all it contains are type definitions that you’ll implement in other code modules (provided they have the EXECUTE privilege on the package):

2. You use the WEAKLY_TYPED_CURSOR function presented earlier in this blog to create a weakly typed cursor as the return type of a stored function.

3. The last step creates a function that translates a weakly typed reference cursor into an aggregate table by using a pipelined function, as shown in the illustration.

The PIPE command transfers a scalar variable or record structure into a row of a target aggregate table, which can be read through the TABLE command in a SQL statement. A neat thing that happens in the example, is that it simply transfers the whole row returned by the cursor as an instance ACTIVE_RECORD into an indexed element of the ACTIVE_COLLECTION collection. The alternative would be syntax like the following:

active_collection(counter).item_title := active_record.item_title;
active_collection(counter).item_title := active_record.item_subtitle;

While those are neat features that may be copied from example code, they’re useless. The more direct way to create this translation program eliminates the collection entirely.

Another alternative would be to do a BULK COLLECT directly into the collection. The next example demonstrates that but you should note that you can’t use a FORALL when assigning collection values to a PIPE for a pipelined function.

4. In SQL, you can query the result using the following syntax:

You can change the prior query to call the use_of_bulk_cursor function to test the bulk collect operation. It didn’t seem worth the effort of doing another screen shot.

More or less, the limitation exists because when operating exclusively inside of PL/SQL there is no way currently to support an Adapter OO pattern. You can implement an Adapter pattern if you use an OCI8 external programming language to read the cursor as a dynamic result set (really only a multi-dimensional array of strings – or technically because the index is sparse a list).

Alternatively in a PL/SQL only solution, you can simply use a strongly typed cursor and bundle all the components into a single program unit. Assuming you create a two column view from the ITEM table, you can use the following query (code base can be downloaded from McGraw-Hill for the Oracle Database 11g PL/SQL Programming book):

If you’d like another example, post a comment to let me know.

Written by maclochlainn

October 11, 2008 at 6:03 am

Is this the look of the new Mac Book Pro?

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It’s amazing what my students discover on the Internet. Not wanting to spoil Apple’s Christmas next week, don’t click through to the full entry or you’ll see a photo and its source URL.

You can find where I found it here, and according to the web page this is what the new Mac Book Pro supposedly will look like:

Written by maclochlainn

October 10, 2008 at 6:30 pm

Posted in Mac

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