MySQL – Fix ERROR 1449 When Restoring Dump

This makes all the sense in the world to me.

InnoDB creates data pages and index pages that are 16K each. If rows of data are being inserted, updated, deleted, committed, and rolled back, you are going to have FRAGMENTATION !!!

There are two cases where you can have internal fragmentation:

• A single row could be written in multiple data pages because certain column values make a row too big to fit in the data page.
• Having a TEXT column with 32K of data in it.

In those two cases, a single row spanning multiple data pages would have to be chained like a linked list. The internally generated list of data pages would always have to be navigated when the row is read.

Giving credit where credit is due, PostgreSQL implemented a very brilliant mechanism called TOAST (The Oversized-Attribute Storage Technique) to keep oversized data outside of tables to stem the tide of this kind of internal fragmentation.

Have used mysqldump to make a file with CREATE TABLE statements, followed by lots of INSERTs, you get a fresh table with no unused space along with contiguous data and index pages when loading the mysqldump into a new server.

For my explanantions, let's assume you have an InnoDB table in the CUSTODIA database called userinfo

If you would like to compress a table, you have three(3) options

Option 1

OPTIMIZE TABLE CUSTODIA.userinfo;

Option 2

ALTER TABLE CUSTODIA.userinfo ENGINE=InnoDB;

Option 3

CREATE TABLE CUSTODIA.userinfo2 LIKE CUSTODIA.userinfo;
INSERT INTO CUSTODIA.userinfo2 SELECT * FROM CUSTODIA.userinfo;
DROP TABLE CUSTODIA.userinfo;
ALTER TABLE CUSTODIA.userinfo2 RENAME CUSTODIA.userinfo;

CAVEAT : Option 3 is no good on a table with constraints. Option 3 is perfect for MyISAM.

Now for your questions:

Question 1. Why is there this difference between original and restored database size?

As explained above

Question 2. Is it safe to assume that restored database is OK, although this difference in size?

If you want to make absolutely sure that the data on both servers are identical, simply run this command on both DB servers:

CHECKSUM TABLE CUSTODIA.userinfo;

Hopefully, the checksum value is identical for the same table on both servers. If you have dozens, even hundreds, of tables, you may have to script it.

Question 3 : How does MySQL calculate data_length? Is it an estimate?

You are using the correct method in summing up the data_length and index_length. Based on my explanation of fragmentation, it is an estimate.

Question 4. Can I safely reduce production's ibdata file size to 3.6GiB with no down-time?

GOOD NEWS !!! You absolutely can compress it !!! In fact, how would like to compress it to a fraction of that number ??? Follow these two links because I addressed this issue in StackOverflow and ServerFault.

https://stackoverflow.com/questions/3927690/howto-clean-a-mysql-innodb-storage-engine/4056261#4056261

https://serverfault.com/questions/230551/mysql-innodb-innodb-file-per-table-cons/231400#231400

BAD NEWS !!! Sorry, but you will have a 3-5 minute window of downtime for rebuilding ib_logfile0 and ib_logfile1 as well shrinking ibdata1 once and for all. It's well worth it since it will be a one-time operation.

Perhaps you should dump the users and load the users into the VM

Here is my post : Export all MySQL users

After running the code in it and saving it to a file called MyDatabaseUSers.sql, you log into mysql on the VM and run this:

mysql> source MyDatabaseUSers.sql

This will create all the users with the same grants and passwords. Don't worry: Passwords are encrypted.

After importing the users, you should be able to reload the mysqldump.

GIVE IT A TRY !!!

NOTE: If you loaded all your data successfully, the error might have occurred loading a MySQL object that has a DEFINER associated with it

• stored procedures
• triggers
• views
• events.

Do the following:

cat newdump.sql | grep -A 2 -n "dc_reporter"

This will show you what might not have loaded. Your data may all be there.

You could try dumping your stored procedures and triggers and reloading them instead of reloading everything. Please read my old post Can mysqldump dump triggers and procedures?, go dump your triggers and stored procedures, and reload them into the VM. If you have views to import, please read my old post Modify DEFINER on Many Views and use the code to mysqldump just the views.