my question is about a database history or transaction log table which is currently updated by mysql procedure. The procedure is called by mysql trigger every time when we keep a history of an appropriate table in during insert, update or delete actions. As far as we have lots of tables for each of them we need to create a separate trigger e.g. for "accounts table" we need to create "accounts_insert, accounts_update and accounts_delete" triggers.
The problem is every time when we alter "accounts table" we have to modify appropriate triggers as well.
Is there any way to avoid that manual work? Would it be better to implement it in application layer/code?
There are no 'global' triggers if that's what you're thinking about.
Application side logging is one possible solution. You'll want to do this within transactions whenever possible.
Other possible approaches:
Create a script that will update your triggers for you. Can be fairly easy, if your triggers are generally similar to each other. Using information_schema database can be helpful here.
Parse general query log (careful, enabling this log can have large negative impact on server's performance)
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i have a system made with MySQL DB and Other system made with PostgreSQL. I want to create an trigger in postgres that insert rows in MySQL, but i don't know how do this, is it posible?
The reason is that i need to syncronize the users of both databases without knowing when the user is created.
You'd have to use mysql_fdw for that.
But I think that it would be a seriously bad idea to do that — if the MySQL database goes down, the trigger will throw an error, and the transaction is undone. Basically, you cannot modify the table any more. Moreover, the latency of the PostgreSQL-MySQL round trip would be added to each transaction.
I think you would be better of with some sort of log table in PostgreSQL where you store the changes. An asynchronous worker can read the changes and apply them on MySQL.
One more thought: You are not considering replicating database users, right? Because you cannot have triggers on system tables.
I would like to get a notification when in certain mysql (or mariadb) tables (innodb) updates,inserts or deletes happen.
I need to track these changes from another process as soon as possible,
I was thinking maybe I could subscribe to the mysql binary log?
Can somebody explain how this can be done?
Is there for example a log read API that mysql offers?
Does the game change when I use a Galera cluster?
You may use mysqlbinlog with --stop-never option to get all insert, update, and delete statements (mysqlbinlog documentation).
You may use the C++ library MySQL Replication Listener that is based on the binlog api.
I don't know if this will help you, but I like to use a separate table to track the changes. If I have a table called "site_visitors", I'll create another table called "site_visitors_log" that is immediately written to with the information I need (IP addresses, timestamp, etc.) right after data is inserted into "site_visitors". Very convenient.
TRIGGER is your friend here. From MySQL-Doc:
A trigger is defined to activate when a statement inserts,
updates, or deletes rows in the associated table
See MySQL-Doc here, there are some examples, too.
I want to create a notification after insertion on some tables. For example whenever a user inserts a comment I create a notification for the administrators that this user has created a comment.
I used to do it manually in the PHP, It wasn't as that bad, It was something like that:
// after the comment is created
Notification::create(....);
Not bad, but sometimes I give the user the ability to add images, posts, ..etc. So I have to remember every time to insert a notification.
So I am thinking of using a mysql trigger instead. But I am worry how that will affect the performance?
One last thing, Is it possible to create a trigger after insert on multiple tables?
Thanks,
Is it possible to create a trigger after insert on multiple tables?
No, it is not possible. You have to create a separate trigger for each table.
I am worry how that will affect the performance?
Performance wise it shouldn't be a disaster although by introducing triggers you artificially prolong insert/update operations on you tables (images, posts, ...) effectively increasing locking time.
But performance is not the only factor to consider. Maintainability should be important too. By creating triggers you scatter you application logic between your app and database. It's harder to test. Triggers are often forgotten e.g. when you transfer the schema or produce a dump. Sometimes you don't want them to fire while you do some maintenance DML on your tables. But MySQL lacks this capability. You'll have to use workarounds for that.
Bottom line: consider not to use triggers unless you have to.
How can one use Triggers for Logging History of database changes in MySQL?
If it is possible, can one create a separate database for trigger tables for tracking history of other Db tables?
maybe you could use this approach instead to do query logging
Is there a way that if there's a change in records, that a query that changed the data (update, delete, insert) can be added to a "history" table transparently?
For example, if mySQL detects a change in a record or set of records, is there a way for mySQL to add that query statement into a separate table so that way, we can track the changes? That would make "rollback" possible since every query (other than SELECT) would be able to reconstruct database from its first row. Right?
I use PHP to interact with mySQL.
You need to enable the MySQL BinLog. This automatically logs all the alteration statements to a binary log which can be replied as needed.
The alternative is to use an auditing function through Triggers
Read about transaction logging in MySQL. This is built in to MySQL.
MySQL has logging functionality that can be used to log all queries. I usually leave this turned off since these logs can grow very rapidly, but it is useful to turn on when debugging.
If you are looking to track changes to records so that you can "roll back" a sequence of queries if some error condition presents itself, then you may want to look into MySQL's native support of transactions.