August 28, 2014

Impossible – possible, moving InnoDB tables between servers

This is probably the feature I missed most from early days when I started to use InnoDB instead of MyISAM. Since that I figured out how to survive without it, but this is first question I hear from customers who migrated from MyISAM to InnoDB – can I just copy .ibd files from one server to another and answer “use mysqldump” is quite disappointed.
Jokes aside, I see real needs in this:
- when we need to restore only single table from backup (sometimes developers kill only single table, not whole database :) )
- to copy single table from production to QA environment. It may sound not so important, but I see needs in this quite often. QA boxes may have their own setup, not so powerful and with not enough space, but QA still needs to have some tables in fresh status.
- resharding databases, moving some shards from one server to another.

So long story short end – we made new mode for XtraBackup, now it can copy and prepare InnoDB/XtraDB tables, which later can be imported into XtraDB.

To be objective the process is still not so easy as with MyISAM tables when you just copy table.frm, table.MYD, table.MYI files, but so nice here – just can copy InnoDB tables in fully non-blocking mode, you do not need to shutdown neither source nor destination server (if destination server runs XtraDB).

In short, process looks like (ah, yes you also need innodb_file_table mode, which ones love, and ones hate)
1) do backup of specific tables on sources server with xtrabackup (server can run InnoDB or XtraDB, it does not matter)
2) do prepare of tables with –export options
3) create table on destination server with exactly the same CREATE TABLE statement as on source. (on destination you should have XtraDB with innodb_expand_import extension and with innodb_expand_import=1 setting)
4) run alter table IMPORTEDTABLE discard tablespace;
5) copy .exp and .ibd files to destination server
6) run alter table IMPORTEDTABLE import tablespace;
7) enjoy progress in error.log like:
InnoDB: import: extended import of test/img_out59
InnoDB: import: 3 indexes are detected.
InnoDB: Progress in %: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 done.

Some more information available on
http://www.percona.com/docs/wiki/percona-xtradb:patch:innodb_expand_import

If you want some internals: I expected the biggest problem with implementation would be merging insert buffer or handling undo records, stored in ibdata file, but it was easy – you just need to shutdown instance with innodb_fast_shutdown=1 (done in xtrabackup –prepare –export call). The more complex problem was that InnoDB stores pointers on root leafs of secondary indexes also in system tablespace. And that’s why we maintain .exp files – to keep information from system tablespace that related to exported table.

Both xtrabackup –export mode and XtraDB innodb_expand_import available only in source code for now, you can get them from Launchpad projects https://launchpad.net/percona-xtradb and https://launchpad.net/percona-xtrabackup. Binary releases will be ready as soon as we have done with testing of this feature. You are welcome to try!

About Vadim Tkachenko

Vadim leads Percona's development group, which produces Percona Clould Tools, the Percona Server, Percona XraDB Cluster and Percona XtraBackup. He is an expert in solid-state storage, and has helped many hardware and software providers succeed in the MySQL market.

Comments

  1. Singer Wang says:

    So, I’m reading this. Does this mean that the eventual table it ends up as is an XtraDB table, not an InnoDB table?

  2. Vadim says:

    Singer,

    For now XtraDB is almost fully compatible with InnoDB table format and backward. So you can import table to XtraDB and after that start InnoDB instance on database.

  3. Mark Callaghan says:

    Wow! This is a great feature to have.

  4. Billy says:

    Can you copy innodb tables across schemas on the same db?

    Ex: Copy schema1.test_table to schema2.test_table

  5. Vadim says:

    Billy,

    Yes, it’s not problem, but again it should be running XtraDB (or InnoDB with patch)

  6. yup, this is a great feature to have

  7. peter says:

    Vadim,

    When some feature is comming so one can do EXPORT TABLESPACE or something similar from MySQL/MariaDB directly ?
    I think this will make such feature much more useful

  8. Hi Vadim,

    Thank you for this excellent post and some really exciting work with XtraDB.

    Would there be any way to achieve the same transfer of a database from one server to another without making an explicit duplicate (backup) copy of the InnoDB data files on the first server in the process?

    I’m considering this in the context of a cluster of machines running XtraDB where we want to “stream” backups of databases from one node (A) to another (B) by using ZFS snapshots rather than query-based MySQL replication. I’d be happy with a short write-block period on A during which the .ibd and .ext files are prepared *in-situ* (so we don’t need to wait while we copy gigabytes of data) and then a snapshot of them is made, at which point the database can un-block and the snapshot can be transmitted to B. Then upon receipt of the snapshot B can do steps 3-7 to get a consistent backup.

    I guess my question is: can XtraBackup be configured / easily patched to do its –export –prepare magic on live XtraDB files rather than a backup copy of them, on the assumption that it’s okay to initiate a write lock on that database for the duration of its action? Also, could XtraDB cope with these files being modified while it’s running?

    I’d be very interested to hear any thoughts you have on this.

    Best Regards,
    Luke Marsden
    Hybrid Logic Ltd.

    http://www.hybrid-cluster.com – Next-generation cloud web hosting

  9. Vadim says:

    Luke,

    I think I got you idea, and it should be possible to implement, but it is not easy ..

    You may contact us http://www.percona.com/contacts.html
    for discussion how we can proceed.

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