Using PostgreSQL Rules/Triggers for debugging purposes - spring

An application I am trying to support is currently running into unique constraint violations. I haven't been able to reproduce this problem in non-production environments. Is it reasonable, for debugging purposes, to create a rule (trigger?) that will in effect just copy every insert to a different table? So in effect the new table will be the same as the old table without a constraint, hopefully.
The application is using Spring to manage transactionality, and I haven't been able to find any documentation relating rules to transactions. After the violation, whatever is written so far in the transaction is rolled back - will this affect the rule in any way?
This is Postgres 8.3.

After the violation, whatever is written so far in the transaction is
rolled back - will this affect the rule in any way?
That will rollback everything the rule did, as well. You could create a trigger that uses dblink, to get some work done outside your current transaction. Another option could be a savepoint, but then you have to change all your current code and transaction.
Unique violations are logged in the logfiles as well, get this information to see what is going wrong. Version 9.0 has a change that will tell you also what the values are:
Improve uniqueness-constraint violation error messages to report the
values causing the failure (Itagaki Takahiro) For example, a
uniqueness constraint violation might now report Key (x)=(2) already
exists.

You can do almost anything you can imagine with rules and triggers. And then some more. Your exact intent remains somewhat unclear, though.
If the transaction is rolled back anyway, as you hint at the end, then everything will be undone, including all side-effects of any rules or triggers involved. Your plan would be futile.
There is a workaround for that in case that is, in fact, what you want to achieve: use dblink to link and INSERT to a table in the same database. That's not rolled back.
However, if it's just for debugging purposes, the database log is a much simpler way to see which duplicates have not been entered. Errors are logged by default. If not, you can set it up as you need it. See about your options in the manual.

As has been said, rules cannot be used for this purpose, as they only serve to rewrite the query. But rewritten query is just like the original one still part of the transaction.
Rules can be used to enforce constraints that are impossible to implement using regular constraints, such as a key being unique among several tables, or other multi-table stuff. (these do have the advantage of the "canary" tablename showing up in the logs and error messages) But the OP already had too many constraints, it appears...
Tweaking the serialisation level also seems indicated (are there multiple sessions involved? does the framework use a connection pool?)

Related

PL/SQL Developer statements sometimes do not commit or "stick"

I apologize if this is too vague, but it is a random issue that occurs with many types of statements. Google and Stack Overflow searches have failed me. Here is what I am experiencing, I hope that someone out there has seen or at least heard of this happening and possibly knows of a solution.
From time to time, with no apparent rhyme or reason, statements that I run through PL/SQL Developer against our Oracle databases do not "stick". Last week I ran an update on table A, a commit for the update statement, then a truncate on table B and an insert to table B followed by another commit. Everything seemed to work fine, as in I received no errors. I was, of course, able to query the changes and see that they were made. However, upon logging out and then back in, the changes had not been committed. Even the truncate command had not worked "stuck" - and truncates do not need a commit performed.
Some details that may be helpful: I am logging into the database server through PL/SQL on a shared account that is used by my team only to gain access to the schema (multiple schemas on each server, each schema has one shared login/PW). Of the 12 people on my team, I am the only one experiencing this issue. I have asked our database administration team to investigate my profile setup and have been told that my profile looks the same as my teammates' profiles. We are forced to go through Citrix to connect to our production database servers. I can only have one instance of PL/SQL open at any time through Citrix, so I typically have PL/SQL connected to several schemas, but I have never been running SQL on more than one schema simultaneously. I'm not even sure if that's possible, but I thought I would mention it. I typically have 3-4 windows open within PL/SQL, each connected to a different schema.
My manager was directly involved in a case where something similar to this happened. I ran four update commands, and committed each one in between; then he ran a select statement only to find that my updates had not actually committed.
I hope that one of my fellow Overflowers' has seen or heard of this issue, or at least may be able to provide me with a direction to follow to attempt to get to the bottom of this.
"it has begun to reflect poorly on me and damage my reputation in the company."
What would really reflect poorly on you would be you believing that an Oracle RDBMS is a magical or random device, or, even worse, sentient and conducting a personal vendetta against you. Computers may seem vindictive but that is always us projecting onto them ;-)
The way to burnish your reputation would be through an informed investigation of the situation. Databases do not randomly lose transactions. So, what is going on?
Possible culprits:
Triggers: does table A have an UPDATE trigger which suppresses some of your SQL?
Synonyms: are tables A and B really the tables you think they are?
Ownership: are these tables in another schema which has row level security enabled (although that should through an error message if you violate a policy)?
PL/SQL Developer configuration: is the IDE hiding error messages or are you not spotting them?
Object types: are tables A and B really tables? Could they be views with INSTEAD OF triggers suppressing some of your SQL?
Object types: or could A and B be materialized views and your session has QUERY_REWRITE_INTEGRITY=stale_tolerated?
If that last one seems a bit of a stretch there other similarly esoteric explanations, involving data flashback, pipelined functions and other malarky. This a category of explanation which indicates a colleague is pranking you.
How to proceed:
Try different tools. SQL*Plus (or the new SQL Command Line) may produce a different outcome. Rule out PL/SQL Developer.
Write some test cases. Strive to establish reproducible test cases: given a certain set-up this SQL statement always leads to a given outcome (SQL always sticks or always does not).
Eliminate bugs or "funnies" in the queries you use to check the results.
Use the data dictionary to understand the characteristics and associated objects of the troublesome tables. You need to understand what causes the different outcomes. What distinguishes a row where the UPDATE holds compared to one where it does not?
I have used PL/SQL Developer for over a decade and I have never known it silently undo successful truncate operations. If it can do that, AA should add it as a menu item. It seems more likely that you ran the commands against the wrong database connection.
I can feel your frustration, sorry you're going through this. I am surprised, however, that at a large company, your change control process is like this. I don't work for a large multi-national company, but any changes done to a production database are first approved by management and run by the DBAs (or in your case, your team). Every script that is run does a few things:
Lists the database instance information its connecting to. For example:
select host_name, instance_name, version, startup_time from v$instance;
Spools the output to a file (the DBAs typically use sqlplus, but I'm sure PL/SQL Developer can do the same)
Shows the current date and time (in the beginning and end of the script)
The output file is saved to a change control server (the directory structure makes it easy to pull any changes for a given instance and/or given timeframe)
Exits on any errors:
WHENEVER SQLERROR EXIT SQL.SQLCODE
Any additional checks that need to be run post script (select counts, etc)
Shows each command that is being run (set echo on), including the commits!
All of this would allow you to not only verify that the script was run successfully, but would allow you to CYOA. Perhaps you can talk with your team about putting some of this in place in your own environment. Hope that helps.
I have no way of knowing if my issue is fixed or not, but here is what I've done:
1. I contacted our company's Citrix team to request that they give my team the ability to have several instances of PL/SQL open. This has been done and so will eliminate the need for one instance with multiple DB connections.
2. I contacted the DBA's and had them remove my old profile, then create a new one with a new username.
So far, all SQL I've run under these new conditions has been just fine. However, I have no way of recreating the issue I'm experiencing so I am just continuing on about my business and hoping for the best.
Should I find a few months from now that I have not experienced this issue again I will update this post in case anyone else experiences it.
Thank you all for the accusations of operator error (screenshots prove that this is not operator error but why should you believe me when my own co-workers have accused me of faking the screenshots) and for the moral support.

Oracle- relying on ROLLBACK for data validation

Is relying on the oracle ROLLBACK command good practice for importing data, validating the data and THEN performing a ROLLBACK?
I've had a data import program built for our ERP, and looking at the code, they insert the data into the real tables, validate, and if it fails validation, they perform a ROLLBACK. I've always validated data before inserting, but just curious if this is an accepted method to rely on?
There are a few things to remember here-
Constraints enable us preserve data integrity. This means that constraints allow us to enforce business rules (or at least the most basic of those) at the database level itself.
A commit or a rollback is a method of preserving or undoing the changes made in a transaction. If you issue a commit after a series of successfully run DML statements, the changes are preserved. The rollback statement would undo the changes.
If, in a series of DML statements, if one of those fails, the effects of that particular statement are rolled back. E.g., if an UPDATE statement updates 10 rows and one of those violates a vital constraint, any of the 10 rows are not updated. Yet, the effects of its preceding statements are not implicitly rolled back.
In order to preserve data integrity and keep the data as per the business requirements, you must issue a manual ROLLBACK statement if any of the DMLs fail.
What you are seeing in your program is the same practice. It doesn't issue a ROLLBACK after a successful transaction, but only after a failed DML, if you look at the code closely. This is indeed a good practice to roll back on failure and commit only if everything goes right.
Front end checks on data are indeed an essential part of any application. This ensures that the data being entered conforms to the business roles. Even in this case, constraints must be applied to perform checks at the database level. This is particularly helpful when some rookie makes changes to the front end and tries to enter invalid data. This is also helpful when someone is bypassing the application and entering data manually. Hence putting constraints on the database level is always necessary.

How can I log changing triggers events?

My task is to make a trigger which will fire when our programmers create, alter, replace or delete triggers in database. It must log their changes to 2 datatables which I made similar to SYS.trigger$ table and added some extra info about user who made changes to them. I copied the principles of logging from already existing audit capability in ERP-system named Galaktika or Galaxy to be simple. However, I encountered a well-famous problem ORA-04089: no one can create triggers on system tables and stuck with it.
Now I'm looking for a way to gently modify my trigger according to database rules. Here is the original code:
CREATE OR REPLACE TRIGGER MRK_AlTrigger$
BEFORE DELETE OR INSERT OR UPDATE
ON SYS.TRIGGER$
REFERENCING NEW AS New OLD AS Old
FOR EACH ROW
DECLARE
Log_Rec MRK_TRIGGERS_LOG_HEADER.NREC%TYPE;
BEGIN
INSERT INTO MRK_TRIGGERS_LOG_HEADER (DATEOFCHANGE,
USERCODE,
OPERATION,
OBJ#)
VALUES (
SYSDATE,
UID,
CASE
WHEN INSERTING THEN 0
WHEN UPDATING THEN 1
WHEN DELETING THEN 2
END,
CASE
WHEN INSERTING OR UPDATING THEN :new.OBJ#
ELSE :old.OBJ#
END)
RETURNING NRec
INTO Log_Rec;
IF INSERTING OR UPDATING
THEN
INSERT INTO MRK_TRIGGERS_LOG_SPECIF (LOGLINK,
OBJ#,
TYPE#,
UPDATE$,
INSERT$,
DELETE$,
BASEOBJECT,
REFOLDNAME,
REFNEWNAME,
DEFINITION,
WHENCLAUSE,
ACTION#,
ACTIONSIZE,
ENABLED,
PROPERTY,
SYS_EVTS,
NTTRIGCOL,
NTTRIGATT,
REFPRTNAME,
ACTIONLINENO)
VALUES (Log_Rec,
:new.OBJ#,
:new.TYPE#,
:new.UPDATE$,
:new.INSERT$,
:new.DELETE$,
:new.BASEOBJECT,
:new.REFOLDNAME,
:new.REFNEWNAME,
:new.DEFINITION,
:new.WHENCLAUSE,
:new.ACTION#,
:new.ACTIONSIZE,
:new.ENABLED,
:new.PROPERTY,
:new.SYS_EVTS,
:new.NTTRIGCOL,
:new.NTTRIGATT,
:new.REFPRTNAME,
:new.ACTIONLINENO);
END IF;
EXCEPTION
WHEN OTHERS
THEN
-- Consider logging the error and then re-raise
RAISE;
END MRK_AlTrigger$;
/
I can also provide MRK_TRIGGERS_LOG_HEADER and MRK_TRIGGERS_LOG_SPECIF DDL, but think it is not necessary. So to make summary, here are the questions I have:
How do I modify the above source to the syntax CREATE OR REPLACE TRIGGER ON DATABASE?
Am I inventing a wheel doing this? Is there any common way to do such things? (I noticed that some tables have logging option, but consider it is for debugging purposes)
Any help will be appreciated!
UPD: I came to decision (thanks to APC) that it is better to hold different versions of code in source control and record only revision number in DB, but dream about doing this automatically.
"We despaired to appeal to our programmers' neatness so my boss
requires that there must be strong and automatic way to log changes.
And to revert them quickly if we need."
In other words, you want a technical fix for what is a political problem. This does not work. However, if you have your boss's support you can sort it out. But it will get messy.
I have been on both sides of this fence, having worked as developer and development DBA. I know from bitter experience how bad it can be if the development database - schemas, configuration parameters, reference data, etc - are not kept under control. Your developers will feel like they are flying right now, but I guarantee you they are not tracking all the changes they make in script form . So their changes are not reversible or repeatable, and when the project reaches UAT the deployment will most likely be a fiasco (buy me a beer and I'll tell you some stories).
So what to do?
Privileged access
Revoke access to SYSDBA accounts and application schema accounts from developers. Apart from anything else you may find parts of the application start to rely on privileged accesses and/or hard-coded passwords, and those are Bad Things; you don't want to include those breaches in Production.
As your developers have got accustomed to having such access this will be highly unpopular. Which is why you need your boss's support. You also must have a replacement approach in place, so leave this action until last. But make no mistake, this is the endgame.
Source control
Database schemas are software too. They are built out of programs, just like the rest of the application, only the source code is DDL and DML scripts not C# or Java. These scripts can be controlled in SVN as with any other source code.
How to organise it in source control? That can be tricky. So recognise that you have three categories of scripts:
Schema scripts which deploy objects
Configuration scripts which insert reference data, manage system parameters, etc
Build scripts which call the other scripts in the right order
Managing the schema scripts is the hardest thing to get right. I suggest you use separate scripts for each object. Also, have separate scripts for table, indexes and constraints. This means you can build all the tables without needing to arrange them in dependency order.
Handling change
The temptation will be to just control a CREATE TABLE statement (or whatever). This is a mistake. In actuality changes to the schema are just as likely to add, drop or modify columns as to introduce totally new objects. Store a CREATE TABLE statement as a baseline, then manage subsequent changes as ALTER TABLE statements.
One file for CREATE TABLE and subsequent ALTER TABLE commands, or separate ones? I'm comfortable having one script: I don't mind if a CREATE TABLE statement fails when I'm expecting the table to already be there. But this can be confusing if others will be running the scripts in say Production. So have a baseline script then separate scripts for applying changes. One alter script per object per time-box is a good compromise.
Changes from developers consist of
alter table script(s) to apply the change
a mirrored alter table script(s) to reverse the change
other scripts, e.g. DML
change reference number (which they will use in SVN)
Because you're introducing this late in the day, you'll need to be diplomatic. So make the change process light and easy to use. Also make sure you check and run the scripts as soon as possible. If you're responsive and do things quickly enough the developers won't chafe under the restricted access.
Getting to there
First of all you need to establish a baseline. Something like DBMS_METADATA will give you CREATE statements for all current objects. You need to organise them in SVN and write the build scripts. Create a toy database and get this right.
This may take some time, so remember to refresh the DDL scripts so they reflect the latest statement. If you have access to a schema comparison tool that would be very handy right now.
Next, sort out the configuration. Hopefully you already know tables contain reference data, otherwise ask the developers.
In your toy database practice zapping the database and building it from scratch. You can use something like Ant or Hudson to automate this if you're feeling adventurous, but at the very least you need some shell scripts to get a build out of SVN.
Making the transition
This is the big one. Announce the new regime to the developers. Get your boss to attend the meeting. Remind the developers to inform you of any changes they make to the database.
That night:
Take a full export with Data Pump
Drop all the application schemas.
Build the application from SVN
Reload the data - but not the data structures - with Data Pump
Hopefully you won't have any structural issues; but if the developer has made changes without telling you you'll know - and they won't have any data in the table.
Make sure you revoke the SYSDBA access as soon as possible.
The developers will need access to a set of schemas so they can write the ALTER scripts. In the developers don't have local personal databases or private schemas to test things I suggest you let them have access to that toy database to test change scripts. Alternatively you can let them keep the application owner access, because you'll be repeating the Trash'n'Rebuild exercise on a regular basis. Once they get used to the idea that they will lose any changes they don't tell you about they will knuckle down and start Doing The Right Thing.
Last word
Obviously this is a lot of vague windbaggery, lacking in solid detail. But that's politics for you.
Postscript
I was at a UKOUG event yesterday, and attended a session by a couple of smart chaps from Regdate. They have a product Source Control for Oracle which provides an interface between (say) SVN and the database. It takes a rather different approach from what I outlined above. But their approach is a sound one. Their tool automates a lot of things, and I think it might help you a lot in your current situation. I must stress that I haven't actually used this product but I think you should check it out - there's a 28 day free trial. Of course, if you don't have any money to spend then this won't help you.
you can find the desierd infos in the following trigger attributes
dictionary_obj_name
dictionary_obj_owner
ora_sysevent
here is the simple ON DATABASE trigger
CREATE OR REPLACE TRIGGER trigger_name
AFTER CREATE OR DROP ON DATABASE
BEGIN
IF dictionary_obj_type = 'TRIGGER'
THEN
INSERT INTO log_table ( trg_name, trg_owner, trg_action) VALUES (dictionary_obj_name,dictionary_obj_owner, ora_sysevent);
END IF;
END;
/

VS2010 Database Project Deployment, to fail if data loss may occur or not?

I have a database project for a web app, and currently I have it configured to fail if data loss may occur during deployment. I feel safer this way. However I've run into a problem. I actually need to deploy changes on some things where I'm okay with the possible data loss, i.e. shortening column lengths where nothing would actually get deleted, but the system thinks it would.
I have 2 questions.
The first is this: other than enabling or disabling the catch all go or no go, is there any way to have more granular control over this process, i.e. specify columns it's okay to drop or shorten? Is there any way to get more granular control of this process?
The second is, how do you guys handle these situations? Initially I had hoped that adding a pre-deployment script to drop the columns would be sufficient, however it seems to catch drops etc. in those files as well.
No there isn't any way to control it at a more granular way unfortunately.
I disable it when I know I'll be deploying something that will cause data loss but is what I want. Then I re-enable it after. Also, I would always check the change script that comes out when deploying to production.
Just update the column in a pre-deployment script to the truncate length?
Eg : to truncate my col to 20 :
UPDATE mycol = LEFT(mycol, 20)
FROM mytable
WHERE mycol != LEFT(mycol, 20)
The Microsoft guidance is to move the data out into a temporary table in pre-deployment, let the deployment engine run a check to see whether the table contains rows (this will pass because it is now empty) and upgrade the schema, and move the data back in a post deployment script.
For more information, see Barclay Hills posts on the subject:
Managing data motion during your deployments (Part 1)
Managing data motion during your deployments (Part 2)

New Oracle Constraint Type

I have to admit that this just caught me by surprise in a production system. I recently added supplemental logging to a few tables for use with Oracle Change Data Capture. A routine check during an unrelated code build revealed that this apparently created disabled constraints in the database of type "S". I can't seem to find any reference to this in the Oracle docs and the single "S" makes it hard to Google for something relevant.
My questions:
Can anyone thing of a reason that
supplemental logging results in an
implicit constraint?
Why is it created with a DISABLED
state?
Does anyone have experience with the
effects of enabling these? We have
a standard clean-up process that
runs after deployments to fully
enable constraints that may have
been disabled or enabled novalidate
for data migration reasons.
Constraint type is documented: http://download.oracle.com/docs/cd/E11882_01/server.112/e10820/statviews_1045.htm#REFRN20047
S stands for "Supplemental logging", which is further explained here: http://download.oracle.com/docs/cd/E11882_01/server.112/e10704/strms_glossary.htm#CHDIHHGA and here: http://download.oracle.com/docs/cd/E11882_01/server.112/e10705/prep_rep.htm#STREP107
I don't have any experience with it. This is the result of searching on tahiti.oracle.com.
Regards,
Rob.
Supplemental logging is necessary to support certain types of asynchronous data capture: AQ Streams for instance, and CDC (both Oracle's and third party's implementations). These mechanisms work by reading the redo logs and applying those changes to some other Oracle database. The point of supplemental logging is to increase the amount of data included in the redo logs, .
There are two ways of enabling supplemental logging. In more recent versions of the database we can set minimal logging at the database level
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
In additional we can add specify tables and columns in Supplemental Log Groups. The point of this is to include the values for unchanged columns in the change table, as it makes it easier to apply the changes in the target database. Find out more.
Obviously the S type constraint identifies columns in a Supplemental Log Group. I think the reason they are disabled is because they do not enforce a data integrity rule (unlike primary keys or check constraints). If so, I think it would be unwise to enable them, and so you should re-write your automatic clean-up to filter constraints of type S.

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