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.
Related
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
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.
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.
I'm doing a venue/events database and I've created my tables and would like some confirmation from someone if I did everything right :)
I have 2 tables:
Venues
Events
The primary key of Venues is VENUE_ID, which is set to auto_increment. I have the same column in Events, which will contain the number of the Venue ID. This should connect them, right?
Also, the table engine is MyISAM.
It does not automatically link the tables to each others, and the referenced columns don't necessarily have to have the same name (in fact, there are situations where this is impossible: e.g. when a table has two columns that both reference the same column in another table).
Read up on foreign keys; they're standard SQL and do exactly what you want. Note, however, that the MyISAM storage engine cannot enforce foreign key constraints, so as long as any of the tables involved uses MyISAM, the foreign key declaration doesn't add much (it does, however, document the relationship, at least in your SQL scripts).
I suggest you use InnoDB (or, if that's feasible, switch to PostgreSQL - not only does it provide foreign key constraints, it also has full support for transactions, unlike MySQL, which will silently commit a pending transaction whenever you do something that's not supported in a transaction, with potentially devastating results). If you have to / want to use MySQL, I suggest you use InnoDB for everything, unless you know you need the extra performance you can get out of MyISAM and you can afford the caveats. Also keep in mind that migrating large tables from MyISAM to InnoDB later in production can be painful or even outright impossible.
Your db structure is right.
You can use Innodb for adding foreign key contraints. Also don't forget to add index to the second table for faster joining two tables.
More info about FK http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
Note to comments:
Innodb allows you to make concurrent select/(insert/update) but MyIsam allows you to do the same things if you don't delete from MyIsam table. Otherwise MyIsam will lock your whole table.
Generally, yes. This is how you indicate a one-to-many relation between two tables. You may also specifically encode the relationship into the database by setting up a Foreign Key constraint. This will allow add'l logic such as cascading.
A client of mine recently formatted his machine and re-installed MySQL Server and my application. He complained that deleting records from master table is not affecting the child tables. I requested him to send the backup of the database. When I restored the database, I found that the Table Engine has changed to MyISAM whereas they were set to InnoDB.
I deleted the records from the child table that were absent in the primary table. After this when I am not re-setting the Foreign Key Index, it displays error: "Foreign key contraint failed. Error 1005" and sometimes error: 150.
I have double checked the rows that might be left in either the primary table or in the child table, but nothing seems to be working.
The primary table has two columns that combinedly form a Primary Key. The columns are: BillNo, BillDate.
Please assist.
This is a widely known MySQL pitfall; I have hit this problem a few times myself. They probably had some problem with InnoDB, and restored their database from backups. Since InnoDB wasn't working, it fell back to the MyISAM storage engine which doesn't support integrity constraints (like foreign keys).
Basically the problem is that, if the InnoDB engine fails to start for whatever reason (usually configuration problems) -- then MySQL silently falls back to the MyISAM engine. Even if your statement says:
CREATE TABLE () ENGINE=InnoDB
then, if InnoDB isn't active, MySQL will happily create a MyISAM table without even warning you. Bye-bye data integrity! :)
You can run SHOW ENGINES to see which engines are active. See this MySQL bug report for more details.
Check that you're using InnoDB engine for both tables.
Check that both fields are of the same type and that they are indexed.
From http://dev.mysql.com/doc/refman/5.0/en/innodb-foreign-key-constraints.html:
If you re-create a table that was
dropped, it must have a definition
that conforms to the foreign key
constraints referencing it. It must
have the right column names and types,
and it must have indexes on the
referenced keys, as stated earlier. If
these are not satisfied, MySQL returns
error number 1005 and refers to error
150 in the error message.