I learned that Liquibase runs each changeSet in a transaction and commits it after inserting into the DATABASECHANGELOG table.
If something goes wrong during the changeSet, the transaction gets rolled back.
My question is, what happens if the changeSet also includes a <rollback> tag.
I know that the rollback tags are used in combination with liquibase dedicated rollback commands, but which one has precedence during a regular migration, the command from the rollback tag or the transaction abortion?
The <rollback> block is not used in when an update fails. If the update fails, Liquibase just calls "rollback" on the connection and relies on the database to correctly roll things back. The <rollback> block is only used when doing the separate rollback command where we're "undoing" the changeset that was already committed in the database.
NOTE: the fact that Liquibase relies on the connection rollback to revert a failed update is why you have to be careful if you have multiple statements in the same changeSet. If you have two createTable calls and your the database auto-commits after the first and the second fails, the rollback on the connection will not roll back the first table. So when you run update the next time, you'll get a table already exists error from the first createTable. The rules on exactly what statements auto-commit are database-specific, so the good rule of thumb is "only one statement per changeset"
Related
Let's say a table has a validation trigger that enforces some business logic:
TRG_MYTABLE_INSERT_UPDATE_VALIDATION
FOR INSERT, UPDATE on MYTABLE
and an audit trigger that writes all inserts and updates to another table.
TRG_MYTABLE_INSERT_UPDATE_AUDIT
FOR INSERT, UPDATE on MYTABLE
and there's no guarantee that they will be executed in a particular order, will a rollback in the VALIDATION trigger rollback the write to the audit table?
Are all of the triggers enlisted in the same transaction "behind the scenes"?
To answer the question about triggers and transactions: yes triggers are enlisted in the same explicit, or implicit, transaction as the code that executes the statement which makes the trigger fire is enlisted in.
Furthermore, in SQL Server triggers runs be default under XACT_ABORT ON which means that if an error happens in the trigger, the WHOLE transaction is rolled back immediately.
So the answer to your question is that if an error happens in either of the triggers, the whole transaction is rolled back.
You can however do a SET XACT_ABORT OFF in your transaction code, in which case, a rollback would only impact whatever you do in the trigger. That is UNLESS your calling code starts a transaction, and you explicitly do a ROLLBACK in your trigger.
The above is why you should be very careful with using triggers in the first place.
What would be the rollback of droptable:
- changeSet:
id: 1
author: vikas
changes:
- sql:
sql: DROP TABLE IF EXISTS `adapter`
What should I put in rollback for the above changeset.
I am getting below error when I was trying to rollback without having rollback tag:
Error setting up or running Liquibase: liquibase.exception.RollbackImpossibleException: No inverse to liquibase.change.core.RawSQLChange created
The error
Error setting up or running Liquibase: liquibase.exception.RollbackImpossibleException: No inverse to liquibase.change.core.RawSQLChange created
happens because you use raw sql, and not the appropriate tag for it (it would be dropTable), so liquibase doesn't know what to do with it. It can't create a rollback.
Also, the documentation says that
Other refactorings such as “drop table” and “insert data” have no corresponding rollback commands that can be automatically generated. In these cases, and cases where you want to override the default generated rollback commands, you can specify the rollback commands via the tag within the changeSet tag. If you do not want anything done to undo a change in rollback mode, use an empty tag.
So you'll have to create a proper rollback for drop table operation.
I don't understand the detailed steps when rolling back using Liquibase.
I had scenario like 6 changesets and for one changeSet rollback was not defined - that is, only <rollback/> within the changeset.
After executing using deployIT I could see 7 entries in Databasechangelog table, 6 for added, one for tag creation due usage of deployIT.
After rolling back I saw the behavior of removing all newly added 6 changesets even though one of the six changesets had an empty rollback tag.
Please any expert tell me why? What is the exact behavior of rollback?
Overall want to know when records from Databasechangelog removed ?
When running rollback, liquibase finds the changeSets to roll back, and then checks for a <rollback> tag in each describing how to roll the changeSet back.
If there is no <rollback> tag, then Liquibase checks if the changes in the changeSet have built-in logic on how to roll themselves back. Like gile pointed out, if there is enough information in the change to undo it (like how the createTable change has the table name needed to drop the table) it will be able to still roll them back.
But if there isn't enough information in the change (like how a dropTable doesn't have the information needed to re-create the table) then the rollback command will fail with a "cannot roll back" error.
So the rollback logic is:
Use what is defined in a block
If no rollback block, try to deduce what is needed
If there isn't enough information to roll back, exit before rolling back
If you specify an empty rollback block, you are telling Liquibase "the logic needed to roll this back is to do nothing", so Liquibase happily runs your no-op rollback command and marks the changeSet as rolled back.
Depending on your change sets, may be you fall in case of statements having rollback commands generated automatically, as for Liquibase Rollback documentation:
Many refactorings such as “create table”, “rename column”, and “add
column” can automatically create rollback statements. If your change
log contains only statements that fit into this category, your
rollback commands will be generated automatically.
Other refactorings such as “drop table” and “insert data” have no
corresponding rollback commands that can be automatically generated.
In these cases, and cases where you want to override the default
generated rollback commands, you can specify the rollback commands via
the tag within the changeSet tag. If you do not want anything done to
undo a change in rollback mode, use an empty tag.
At http://forum.liquibase.org/topic/understanding-rollback you can find more details and other links.
I am new to Liquibase and I am trying to get the rollback feature working. I am running Liquibase in Windows. I executed an install which tagged the database at version_1.0. I ran an update which tagged the database at version_1.1. Now I am trying to rollback to version_1.0
Here is the command I am running:
liquibase rollback version_1.0
this gives an error that a --changeLogFile is needed so I ran this
liquibase --changeLogFile=v001/master.xml rollback version_1.0
I provide the name of the change log file that was executed during the update, but nothing gets. The update contains 2 create table statements and the tables were not dropped. What am I missing in the rollback process?
Liquibase does not tag the database really. It only tags to know which changessets need to be rolled back.
The rollback will be done by execute the rollback tags in the changeling.
If i run change log file that contain multiple change set from command line and it failed because of wrong sql at say change set 2. So change set 1 has executed and committed then how will i rollback this change using liquibase.
The easiest would be to use the rollbackCount command. Running "liquibase rollbackCount 1" will roll back the last changeSet executed using either the specified <rollback> block in the changeSet or by figuring it out if Liquibaes can based on the information in the changeSet. For example, a createTable command has the information needed to create a drop table statement, but a dropTable command does not have the information needed to do a create table so you would need to specify your own rollback block.