Thursday, 14 May 2015

How to keep track of execution in multi-file/part Oracle scripts

disclaimer: here

Installation scripts can be a pain.

With multiple anonymous PL/SQL blocks here and there, and scripts calling other scripts and bind variables being initiated through running some other scripts and.... You get the image.

So if -God forbid- we want to check the result of an activity which might have happened in the earlier parts of this "spaghetti of codes," we need to kill a bunch of those precious gray cells and find a way!

Must of the time decisions can be based on "footprints in the data;" e.g. something is supposed to happen later in the script based on whether we have deleted a row or not. But If the script is supposed to be re-runnable (such as an installation/upgrade/patch script) how can you judge whether THAT rows has been dropped in this run, or a previous one?

Well, there is a solution after all.

Conditional Compilation Flags to the rescue!

As long as your script is running on an 10gR2 or later released instance, and your whole script runs in one session, you can use the session variables, aka Conditional Compilation Flags.

Their biggest advantage is that unlike the bind variables (set by DEFINE command), you can set/unset your session variables inside OR outside a PL/SQL block.


ALTER SESSION SET PLSQL_CCFLAGS = 'flagName:value[,flag2Name:value2, ...]';

or inside a block:

EXECUTE IMMEDIATE 'ALTER SESSION SET PLSQL_CCFLAGS = ''flagName:value[,flag2Name:value2, ...]''';

Example Scenario

Imagine the following "install.sql" script (positioned in the same directory as "one.sql" and "two.sql"



This sample script has two parts. The first anonymous block simulates an activity that whose result affect the operation (i.e. code-path) in the second script in the same file, and consequently the operation in a second file.

The first script populates a flag named "activityResult" (Note: Conditional Compilation Flags are case-sensitive) with either 0 or 1, depending on the results of the simulated operation.

The second script shows how can you check the value of the flag and create alternative code-paths.

$IF ... $THEN $ELSIF $ELSE $END is THE construct when it comes to Conditional Compilation.

The flags themselves are referred to as $$flagName.

        v_RandomActivityResult  NUMBER := CEIL(DBMS_RANDOM.VALUE(0,6));
        dbms_output.put_line('script one - first block');
        dbms_output.put_line('Random Activity Result:' || to_char(v_RandomActivityResult));

        IF v_RandomActivityResult < 3 THEN
                -- Failure
                EXECUTE IMMEDIATE 'alter session set PLSQL_CCFLAGS = ''activityResult:0''';
                -- Success
                EXECUTE IMMEDIATE 'alter session set PLSQL_CCFLAGS = ''activityResult:1''';
        END IF;

        dbms_output.put_line('script one - second block');
$IF $$activityResult = 1 $THEN
        dbms_output.put_line('The activity in the first block was successful!');
        dbms_output.put_line('Carrying out related activity...');
        EXECUTE IMMEDIATE 'alter session set PLSQL_CCFLAGS = ''relatedActivity:1''';
        dbms_output.put_line('The activity in the first block failed!');
        EXECUTE IMMEDIATE 'alter session set PLSQL_CCFLAGS = ''relatedActivity:0''';


The "one.sql" showed that it is possible to access a session flag inside an anonymous block which hasn't populated/initiated the flag. The following script simply provides an example to clarify what does "session" mean!

        dbms_output.put_line('script two');
$IF $$relatedActivity = 1 $THEN
        dbms_output.put_line('Related activity was carried out.');
        dbms_output.put_line('Related activity was not carried out.');

A sample output:

"two.sql" is merely another file which (as can be seen above) is run as part of "install.sql" so it's still in the same session, and can access the "relatedActivity" flag that was initiated in the second block inside "one.sql."

$ sqlplus /nolog @install

SQL*Plus: Release Production on Thu May 14 14:20:00 2015

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Session altered.

script one - first block
Random Activity Result:1

PL/SQL procedure successfully completed.

script one - second block
The activity in the first block failed!

PL/SQL procedure successfully completed.

script two
Related activity was not carried out.

PL/SQL procedure successfully completed.

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This post was an extremely simple implementation of what's being offered by Oracle through the concept of Conditional Compilation, and the directives are not limited to what were used in this post.

You can find Oracle's reference on the subject here.

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