Tag: Backup

Announcing orchestrator-agent

MySQL

orchestrator-agent is a side-kick, complementary project of orchestrator, implementing a daemon service on one’s MySQL hosts which communicates with and accepts commands from orchestrator, built with the original purpose of providing an automated solution for provisioning new or corrupted slaves.

It was built by Outbrain, with Outbrain’s specific use case in mind. While we release it as open source, only a small part of its functionality will appeal to the public (this is why it’s not strictly part of the orchestrator project, which is a general purpose, wide-audience solution). Nevertheless, it is a simple implementation of a daemon, such that can be easily extended by the community. The project is open for pull-requests!

A quick breakdown of orchestrator-agent is as follows:

  • Executes as a daemon on linux hosts
  • Interacts and invokes OS commands (via bash)
  • Does not directly interact with a MySQL server running on that host (does not connect via mysql credentials)
  • Expects a single MySQL service on host
  • Can control the MySQL service (e.g. stop, start)
  • Is familiar with LVM layer on host
  • Can take LVM snapshots, mount snapshots, remove snapshots
  • Is familiar with the MySQL data directory, disk usage, file system
  • Can send snapshot data from a mounted snapshot on a running MySQL host
  • Can prepare data directory and receive snapshot data from another host
  • Recognizes local/remote datacenters
  • Controlled by orchestrator, two orchestrator-agents implement an automated and audited solution for seeding a new/corrupted MySQL host based on a running server.

Continue reading » “Announcing orchestrator-agent”

A new MySQL backups temperature scale, with showers

MySQL

We’re used to Cold, Warm and Hot backups. This scale of three temperatures does not quite reflect the impact of backups on your MySQL database.

In this post I offer a new backup temperature scale, and (somewhat seriously) compare it with showers. Call it the backup shower scale.

A database backup is like a shower: the colder it is, the less time you want to spend doing it.

Cold

A cold backup requires taking your database down (i.e. stop the service).

Example: file system copy

This can work well for replicating slaves, which may not be required for normal operation. You take the slave down, turn off the service, make your backup, turn everything on again, and let the backup catch up. Just make sure its master has all the necessary binary logs.

A friend was staying at my place and was lecturing me on the benefits of cold showers; how it was good for your health. A couple hours later, preparing for bed, I hear him exclaiming from the bathroom: “Whaaaaa! There’s no hot water!” Continue reading » “A new MySQL backups temperature scale, with showers”

Upgrading to Barracuda & getting rid of huge ibdata1 file

MySQL

Some of this is old stuff, but more people are now converting to InnoDB plugin, so as to enjoy table compression, performance boosts. Same holds for people converting to Percona’s XtraDB. InnoDB plugin requires innodb_file_per_table. No more shared tablespace file.

So your ibdata1 file is some 150GB, and it won’t reduce. Really, it won’t reduce. You set innodb_file_per_table=1, do ALTER TABLE t ENGINE=InnoDB (optionally ROW_FORMAT=COMPRESSED KEY_BLOCK_SIZE=8), and you get all your tables in file-per-table .ibd files.

But the original ibdata1 file is still there. It has to be there, don’t delete it! It contains more than your old data.

InnoDB tablespace files never reduce in size, it’s an old-time annoyance. The only way to go round it, if you need the space, is to completely drop them and start afresh. That’s one of the things so nice about file-per-table: an ALTER TABLE actually creates a new tablespace file and drops the original one.

The procedure

The procedure is somewhat painful:

An argument for using mysqldump

MySQL

I fully agree with Morgan’s An argument for not using mysqldump. This post does not come to contradict it, but rather shed a positive light on mysqldump.

I usually prefer an LVM snapshot based backup, or using XtraBackup. And, with databases as large as dozens of GB and above, I consider mysqldump to be a poor alternative. Poor in runtime, poor in overhead while taking the backup.

However once in a while I get to be reminded that mysqldump just works.

As a recent example, I had a server which was killed after an ALTER TABLE statement hanged forever (table already ALTERed, but old scheme never dropped). The old table data still hanged around the file system, but was not recognized by InnoDB. Trying out DISCARD TABLESPACE did not do the job, and eventually file was dropped.

So far, reasonable. InnoDB would complain about some table it never recognized in the first place, but all would work. That is, until backup was concerned. With innobackup or XtraBackup the restore would fail on some internal problem. LVM would work, but would only copy+paste the problem: innobackup would never again be able to be used on this database. Continue reading » “An argument for using mysqldump”

mylvmbackup HOWTO: minimal privileges & filesystem copy

MySQL

This HOWTO discusses two (unrelated) issues with mylvmbackup:

  • The minimal privileges required to take MySQL backups with mylvmbackup.
  • Making (non compressed) file system copy of one’s data files.

Minimal privileges

Some just give mylvmbackup the root account, which is far too permissive. We now consider what the minimal requirements of mylvmbackup are.

The queries mylvmbackup issues are:

  • FLUSH TABLES
  • FLUSH TABLES WITH READ LOCK
  • SHOW MASTER STATUS
  • SHOW SLAVE STATUS
  • UNLOCK TABLES

Both SHOW MASTER STATUS & SHOW SLAVE STATUS require either the SUPER or REPLICATION CLIENT privilege. Since SUPER is more powerful, we choose REPLICATION CLIENT.

The FLUSH TABLES * and UNLOCK TABLES require the RELOAD privilege.

However, we are not done yet. mylvmbackup connects to the mysql database, which means we must also have some privilege there, too. We choose the SELECT privilege.

Continue reading » “mylvmbackup HOWTO: minimal privileges & filesystem copy”

Tips for taking MySQL backups using LVM

MySQL

LVM uses copy-on-write to implement snapshots. Whenever you’re writing data to some page, LVM copies the original page (the way it looked like when the snapshot was taken) to the snapshot volume. The snapshot volume must be large enough to accommodate all pages written to for the duration of the snapshot’s lifetime. In other words, you must be able to copy the data somewhere outside (tape, NFS, rsync, etc.) in less time than it would take for the snapshot to fill up.

While LVM allows for hot backups of MySQL, it still poses an impact on the disks. An LVM snapshot backup may not go unnoticed by the MySQL users.

Some general guidelines for making life easier with LVM backups follow.

Lighter, longer snapshots

If you’re confident that you have enough space on your snapshot volume, you may take the opportunity to make for a longer backup time. Why? Because you would then be able to reduce the stress from the file system. Use ionice when copying your data from the snapshot volume:

ionice -c 2 cp -R /mnt/mysql_snapshot /mnt/backup/daily/20100719/

[Update: this is only on the cfq I/O scheduler; thanks, Vojtech]

Are you running out of space?

Monitor snapshot’s allocated size: if there’s just one snapshot, do it like this: Continue reading » “Tips for taking MySQL backups using LVM”

A MyISAM backup is blocking as read-only, including mysqldump backup

MySQL

Actually this is (almost) all I wanted to say. This is intentionally posted with all related keywords in title, in the hope that a related search on Google will result with this post on first page.

I’m just still encountering companies who use MyISAM as their storage engine and are unaware that their nightly backup actually blocks their application, basically rendering their product unavailable for long minutes to hours on a nightly basis.

So this is posted as a warning for those who were not aware of this fact.

There is no hot (non blocking) backup for MyISAM. Closest would be file system snapshot, but even this requires flushing of tables, which may take a while to complete. If you must have a hot backup, then either use replication – and take the risk of the slave not being in complete sync with the master – or use another storage engine, i.e. InnoDB.

Defined your MySQL backup & recovery plan recently?

MySQL

Following up on Ronald Bradford‘s Checked your MySQL recovery process recently? post, I wish to add a prequel.

To see whether you have a clear definition of your backup requirements, ask yourself these questions:

  • Is there a backup/restore plan?
  • Is there a written backup/restore plan?
  • How fast do you need to recover a backup? What’s the longest downtime you will allow from the point of failure to the point of restored, functional database?
  • How much data are you willing to lose in case of crash? A second’s worth of data? An hour’s worth? A day’s worth? None?
  • Are you willing to allow that the database becomes read-only when taking the backup? Or completely down?
  • Are you willing to take the risk that the backup will not be 100% compatible with the data? (Backing up your slave holds this risk)
  • Is your manager willing to all that you are willing?
  • Is the backup plan known to the management team, or do they just know that “the database has backups“?

The above checklist is by no means complete.

I have a vivid memory of a very good sys admin who failed on the last two points. He had some very sour days when recovering a lost file from tape took much longer than was affordable to some contract.

I found that technical people rarely share the same views as marketing/management. Make sure to consult with the management team; they will have a clearer view on what the company can afford and what it cannot afford.

On restoring a single table from mysqldump

MySQL

Following Restore one table from an ALL database dump and Restore a Single Table From mysqldump, I would like to add my own thoughts and comments on the subject.

I also wish to note performance issues with the two suggested solutions, and offer improvements.

Problem relevance

While the problem is interesting, I just want to note that it is relevant in very specific database dimensions. Too small – and it doesn’t matter how you solve it (e.g. just open vi/emacs and copy+paste). Too big – and it would not be worthwhile to restore from mysqldump anyway. I would suggest that the problem is interesting in the whereabouts of a few dozen GB worth of data.

Problem recap

Given a dump file (generated by mysqldump), how do you restore a single table, without making any changes to other tables?

Let’s review the two referenced solutions. I’ll be using the employees db on mysql-sandbox for testing. I’ll choose a very small table to restore: departments (only a few rows in this table).

Security based solution

Chris offers to create a special purpose account, which will only have write (CREATE, INSERT, etc.) privileges on the particular table to restore. Cool hack! But, I’m afraid, not too efficient, for two reasons: Continue reading » “On restoring a single table from mysqldump”

Parameters to use on mysqldump

MySQL

mysqldump is commonly used for making a MySQL database backup or for setting up a replication.

As in all mysql binaries, there are quite a few parameters to mysqldump. Some are just niceties but some flags are a must. Of course, choosing the parameters to use greatly depends on your requirements, database setup, network capacity etc.

Here is my usual setup for mysqldump. The parameters below apply for an InnoDB based schema (no MyISAM, Memory tables). Parameters can be specified on the command line, or under the [mysqld] scope in the MySQL configuration file.

mysqldump -u dump_user -p -h db_host --routines --master-data --single-transaction  --skip-add-locks --skip-lock-tables --default-character-set=utf8 --compress my_db

Let’s review these parameters and see their effect: Continue reading » “Parameters to use on mysqldump”