My database is currently using the InnoDB engine. Now I want to add the fulltext search feature, which is why I want to convert my tables to MyISAM. But doing so breaks all foreign keys. How can I change my table engines to MyISAM safely?
How can I use SELECT...JOIN after I change my tables to the MyISAM engine?
ALTER TABLE jobs ENGINE = MyISAM;
Cannot delete or update a parent row: a foreign key constraint fails
I'd recommend you to do a dump of the db, change all the text from that file from InnoDB to MyISAM, then load the modified file
As I know, MyISAM doesn't supports foreign keys (compare the features offered by InnoDB vs the features of MyISAM). MySQL tries to tell you that you have to drop every foreign key constraint that references your jobs table before changing its engine to MyISAM.
Related
I keep hearing that InnoDB is better for data integrity, unfortunately as of MySQL 5.6 it has yet to support SPATIAL indexes. A fast SPATIAL index is pretty critical to my app, though what's nice about my model that it's pretty much results in a fairly static (write once, read many) table of (ID, POINT), so I could use MyISAM and not care too much.
I'd like to restrict the use of MyISAM to just that table, and migrate it over when InnoDB support for SPATIAL is ready. Problem is, if I ALTER TABLE after my models are migrated (by having an app/sql/app_model.sql) to switch the table to MyISAM, MySQL complains:
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
That makes sense, my other models refer to this one and Django automatically makes FOREIGN KEY constraints between those models and this one.
What's the best strategy here? Should I abandon InnoDB and switch everything back to MyISAM? Can I just drop all the FOREIGN KEY constraints?
I tried automating the FOREIGN KEY drops by looking in INFORMATION_SCHEMA.TABLE_CONSTRAINTS, but that only lists the tables that have the constraints, not the tables referred to by those constraints. I would have to do some fuzzy column name matching which feels very brittle.
To solve this I gave up on using InnoDB by default. Because Amazon RDS makes Inno the default, I did this by adding an init_command in my settings.py:
'default': {
'OPTIONS': {
'init_command' : 'SET storage_engine=MYISAM', # Can't make SPATIAL keys on InnoDB
},
}
Then for all but the table with a SPATIAL index I created a $modelname.sql file under the $appname/sql directory that changes the engine after it's created.
-- Alter to InnoDB so we can make concurrent insertions w/o full table lock.
ALTER TABLE <modeltable> ENGINE=INNODB;
Switching to MYISAM default means Django doesn't automatically create the FOREIGN KEY constraints for you for your Inno tables which isn't ideal. I wish there was a way to make Django create them after-the-fact.
I am writing a web-app for my studies which includes fulltext search and foreign keys.
I have read somewhere, MyISAM engine is suitable for fulltext searching, and InnoDB for foreign keys.
In this situation what engine should I use for the best performance?
Why does MyISAM not support foreign key relationship but InnoDB does?
Why does MyISAM support full text search but InnoDB does not?
Kindly tell me, In this situation what engine I have to use for improve performance?
The performance of each storage engine will depend on the queries you perform. However, be aware that different tables within the same database can use different storage engines.
Why MyISAM engine does not support foreign key relationship and InnoDB does?
As documented under Foreign Key Differences:
At a later stage, foreign key constraints will be implemented for MyISAM tables as well.
Therefore, foreign key constraints have simply not yet been implemented in MyISAM.
EDIT: As that comment is removed from docs, it appears that it is no longer planned to implement foreign key constraints in MyISAM engine.
Why MyISAM engine does support full text search and InnoDB does not?
As documented under What Is New in MySQL 5.6:
You can create FULLTEXT indexes on InnoDB tables, and query them using the MATCH() ... AGAINST syntax.
Therefore, full text search has been implemented in InnoDB as of MySQL 5.6.
I do remember the times when mysql had only myisam and innodedb was in development. MyIsam has no foreign keys because it is old system that does not support relations in database. It will never use foreign keys! To Use it you have innodb. If you don't need all stuff, like relations in DB, use MyISAM to get better performance.
Can anyone tell me if MySQL does indexing for its foreign keys automatically or not?
My MySQL is using MyIsam Engine.
MyISAM does not support foreign keys at all. From the manual:
For storage engines other than InnoDB, MySQL Server parses the FOREIGN
KEY syntax in CREATE TABLE statements, but does not use or store it.
... At a later stage, foreign key constraints will be implemented for
MyISAM tables as well.
This is for MySQL 5.6, the next version, so it is not implemented yet. The text is exactly the same for older versions.
This means that the foreign key construct is not used at all. You can specify it in your CREATE TABLE command but MySQL will silently ignore it. No index will be made out of it, and it won't be stored (so a SHOW CREATE TABLE command will not show that you tried to createa a foreign key).
If you need foreign key support, consider using the InnoDB storage engine instead. InnoDB creates indices automatically for foreign keys.
MyISAM engine doesn't support foreign keys, only the InnoDB engine:
http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
InnoDB requires indexes on foreign keys and referenced keys so that
foreign key checks can be fast and not require a table scan. In the
referencing table, there must be an index where the foreign key
columns are listed as the first columns in the same order. Such an
index is created on the referencing table automatically if it does not
exist. This index might be silently dropped later, if you create
another index that can be used to enforce the foreign key constraint.
index_name, if given, is used as described previously.
So, in the process of creating our tables, we weren't paying close enough attention to our system and all of the tables were created with the InnoDB engine. This is really only bad because we want to have a FULLTEXT index on a few of the columns.
So, now I want to convert. And while I'm at it, I just want to convert all the tables to MyISAM so that if we ever add columns in the future that we want to index, we have that option. So I've got my .sql file with the following:
ALTER TABLE tableName1 Engine = MyISAM;
ALTER TABLE tableName2 Engine = MyISAM;
However, when I try to run it, I get the following error:
Error Code: 1217 Cannot delete or update a parent row: a foreign key constraint fails
As you might have guessed, we have foreign keys in our tables. Not my style, but also not my department, nor my creation script.
My question boils down to, is there anyway for me to change the engine on these tables without having to wipe the DB?
Edit: Note that this will need to be done on multiple development and test copies of the database, so something I can script would definitely be preferred.
Well, to my knowledge, sort of but not really. mysqldump the database and edit out the foreign key constraints in the dumped sql file. And of course change the engine in the CREATE TABLE script.
InnoDB unlike MyISAM support foreign keys and has lots of great features like transactional system that ensures integrity across all tables. MyISAM tables tend to fail now and then when you have large data in tables or for many other reasons.
In the near future InnoDB will implement FullText search. I recommend not to change tables' engine but have something like Sphinx in place. Sphinx is much more powerful and much more flexible than Fulltext Search which works for InnoDB.
More about fulltext search in InnoDB:
InnoDB Fulltext search
I currently have a database based on a MYISAM storage engine that has a few thousand records. I want to convert my database over to InnoDb storage engine.
It won't be a simple ALTER storage engine command, since I need to add foreign keys to to the current database schema( the current MyISAM db schema does have primary keys though) before I convert it over to InnoDb.
My question is once I convert the DB over to InnoDb would restoring the data from the current MYISAM engine to InnoDb engine would be as simple as firing a PhpMyAdmin instance and back up the data (minus the db schema or structure) and then restore it to the Innodb engine?
What are the potential hurdles in doing this?
Is this the correct way to go about this or what are the various other easier or better ways to restore data?
It won't be a simple ALTER storage engine command, since i need to add foreign keys to to the current database schema
Why not? Sure backup the data first, that is always a good idea, but you don't need to dump and restore the data, you can issue your simple ALTER TABLE, such as:
ALTER TABLE `tablename` ENGINE = InnoDB;
After that you can add any index and foreign key. If any new foreign key fails, you've to fix your data and try again.
When you add foreign keys first, you have to copy your data in a certain order, otherwise your data won't be added because of foreign key constraints.
Therefore, the best thing is checking (through SQL queries) if you can fulfill your foreign key constraints with your current dataset, then copy the data, afterwards, define foreign keys.
But if you export your data from an InnoDB database with PHPMyAdmin, the order is already fulfilled and you can re-import it without any problems.
You could probably add the foreign keys later
Alter the table to use a new engine
Alter each table to use foreign keys
I only see one issue with that and that would be if the foreign keys are broken to start with.