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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for May 25th, 2021

Happy Towel Day: today is the 42nd towel day in remembrance of a truly remarkable author.

Posted by jpluimers on 2021/05/25

Happy Towel Day!

Today is the 42nd towel day in remembrance of a truly remarkable author.

jeroen

Posted in About, Comics, Fun, Opinions, Personal | Leave a Comment »

How to do tnsping? | Oracle Community

Posted by jpluimers on 2021/05/25

Since How to do tnsping? | Oracle Community refuses to be archived in the WayBack archive and Archive.is, here a quote of the most important part in the thread:

EdStevensGrand Titan

Boopathy Vasagam wrote:
How to do tnsping?
I am new to databse.
i am using Oracle 10.2 database in windows XP. How to do ‘tnsping’ in that?

Others are helping you with how to run a command. In anticipation of what your next question will be ….

Assume you have the following in your tnsnames.ora:

larry =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = myhost)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = curley)
    )
  )

Now, when you issue a connect, say like this:

$> sqlplus scott/tiger@larry

tns will look in your tnsnames.ora for an entry called ‘larry’. Next, tns sends a request to (PORT = 1521) on (HOST = myhost) using (PROTOCOL = TCP), asking for a connection to (SERVICE_NAME = curley).

Where is (HOST = myhost) on the network? When the request gets passed from tns to the next layer in the network stack, the name ‘myhost’ will get resolved to an IP address, either via a local ‘hosts’ file, via DNS, or possibly other less used mechanisms. You can also hard-code the ip address (HOST = 123.456.789.101) in the tnsnames.ora.

Next, the request arrives at port 1521 on myhost. Hopefully, there is a listener on myhost configured to listen on port 1521, and that listener knows about SERVICE_NAME = curley. If so, you’ll be connected.

A couple of important points.

First, the listener is a server side only process. It’s entire purpose in life is the receive requests for connections to databases and set up those connections. Once the connection is established, the listener is out of the picture. It creates the connection. It doesn’t sustain the connection. One listener, running from one oracle home, listening on a single port, will serve multiple database instances of multiple versions running from multiple homes. It is an unnecessary complexity to try to have multiple listeners. That would be like the telephone company building a separate switchboard for each customer.

Second, the tnsnames.ora file is a client side issue. It’s purpose is for addressess resolution – the tns equivelent of the ‘hosts’ file further down the network stack. The only reason it exists on a host machine is because that machine can also run client processes.

What can go wrong?

First, there may not be an entry for ‘larry’ in your tnsnames. In that case you get “ORA-12154: TNS:could not resolve the connect identifier specified” No need to go looking for a problem on the host, with the listener, etc. If you can’t place a telephone call because you don’t know the number (can’t find your telephone directory (tnsnames.ora) or can’t find the party you are looking for listed in it (no entry for larry)) you don’t look for problems at the telephone switchboard.

Maybe the entry for larry was found, but myhost couldn’t be resolved to an IP address (say there was no entry for myhost in the local hosts file). This will result in “ORA-12545: Connect failed because target host or object does not exist”

Maybe there was an entry for myserver in the local hosts file, but it specified a bad IP address. This will result in “ORA-12545: Connect failed because target host or object does not exist”

Maybe the IP was good, but there is no listener running: “ORA-12541: TNS:no listener”

Maybe the IP was good, there is a listener at myhost, but it is listening on a different port. “ORA-12560: TNS:protocol adapter error”

Maybe the IP was good, there is a listener at myhost, it is listening on the specified port, but doesn’t know about SERVICE_NAME = curley. “ORA-12514: TNS:listener does not currently know of service requested in connect descriptor”

Also, please be aware that tnsping goes no further than to verify there is a listener at the specified host/port. It DOES NOT prove anything regarding the status of the listener’s knowledge of any particular database instance.

–jeroen

Posted in Database Development, Development, OracleDB, Software Development | Leave a Comment »

Some VMS and DCL history links

Posted by jpluimers on 2021/05/25

Last week, I wrote about a bit of my command-line and scripting history at I wanted to know the loaded DLLs in a process like Process Explorer shows, but from the console: Sysinternals ListDLLs to the rescue.

Since information about VMS and DCL is harder to find nowadays, I saved some information in the wayback machine:

By now, there should be a good x86_64 version of OpenVMS, so this is also a reminder to self to see if that can run as a VM and is affordable enough to do some experimentation with.

–jeroen

Posted in Development, History, Scripting, Software Development | Leave a Comment »

Delphi: creating copies of installed components to repositories for portability across use cases

Posted by jpluimers on 2021/05/25

Often it is useful to have 3rd party components part of a repository so it is easier to increase portability.

For instance when you want to include or exclude some of them in certain projects by installing/deinstalling them to/from the IDE.

This can be useful for cases where components bite each other, or you want to vary the components in use by version without spinning up new VMs (Delphi registration counts can be a pain for new VMs; you need to be very careful as you can never decrease your registration count).

I usually do this by having 3 batch files:

  1. copy from an installed 3rd party library to a repository in a relative way
  2. register any needed relative files into the IDE
  3. unregister any needed relative files in from the IDE

If successful, I can uninstall the library.

I especially take this approach with 3rd party libraries that stuff to global places (inside the Delphi installation directory, or worse, inside the Windows directories).

That way, I can try to ensure that compilation of running only uses files from the repository, making my options for portability larger.

Examples I did this for are for instance QuickReports and ODAC.

Some bits are tricky to get right, especially loading dependencies.

It helps to understand that for executable files Windows also searches for dependencies in the directory of the executable file.

For libraries, that does not happen. Which means that if a BPL has dependencies, they either have to be explicitly loaded before (for instance by being in the Known Packages registry entries), or on the search PATH.

Delphi has the %BDSCOMMONDIR% directory in the search PATH. It usually points to “%PUBLIC%\Documents\Embarcadero\Studio\%ProductVersion%\Bpl” (where ProductVersion=19.0 for Delphi 10.2 Tokyo).

There might be a away around this using manifests, but this means modifying the BPL files, which is beyond the point of having these copy scripts.

More on those environment variables in a later blog post.

Related:

–jeroen

Read the rest of this entry »

Posted in Conference Topics, Conferences, Delphi, Delphi 10.2 Tokyo (Godzilla), Development, Event, Software Development | Leave a Comment »

 
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