Sorry Mark - I thought your question was more of a "does this seem
right" and "how do I" than a "something's wrong here" post.

I think your problem is coming in with the use of --opt.  The article
you reference, where it says "This is an online, non-blocking backup",
makes no mention of --opt, which as you note includes --lock-tables.
From mysqldump man page:

--lock-tables, -l

         Lock all tables before starting the dump. The tables are locked with
         READ LOCAL to allow concurrent inserts in the case of MyISAM tables.
         For transactional tables such as InnoDB and BDB,
         --single-transaction is a much better option, because it does not
         need to lock the tables at all.

         Please note that when dumping multiple databases, --lock-tables
         locks tables for each database separately. So, this option does not
         guarantee that the tables in the dump file are logically consistent
         between databases. Tables in different databases may be dumped in
         completely different states.

Try running without --opt, possibly specifying the included options
you need individually, and see if that works better for you.

I understand what you're saying about MySQL replication; hence the
need for monitoring the replication to ensure good backups.

Dan




On 7/10/06, Mark Steele <[EMAIL PROTECTED]> wrote:
Hi Dan,


  --single-transaction
          Creates a consistent snapshot by dumping all tables in a
          single transaction. Works ONLY for tables stored in
          storage engines which support multiversioning (currently
          only InnoDB does); the dump is NOT guaranteed to be
          consistent for other storage engines. Option
          automatically turns off --lock-tables.
  --opt
          Same as --add-drop-table, --add-locks, --create-options,
          --quick, --extended-insert, --lock-tables, --set-charset,
          and --disable-keys. Enabled by default, disable with
          --skip-opt.

See http://dev.mysql.com/doc/refman/5.0/en/backup-policy.html

These options should produce a non-blocking consistent database
snapshot.

I can already accomplish this on a slave server, however MySQL
replication can lead to slave drift as it is statement based (as opposed
to row-based replication). The only safe way to guarantee a real backup
in a MySQL replication setup is via snapshots on the master.

-----Original Message-----
From: Dan Buettner [mailto:[EMAIL PROTECTED]
Sent: Monday, July 10, 2006 2:42 PM
To: Mark Steele
Cc: mysql@lists.mysql.com
Subject: Re: mysqldump with single-transaction with high-concurrency DB

Mark, that's the expected behavior of mysqldump with --opt and
--single-transaction; it locks all databases and all tables for the
duration of the dump, ensuring a consistent snapshot.

With a database this size (100 GB), it's an area where throwing
hardware at the problem may be your best bet.  I suggest one of two
approaches as possible solutions:

1) Buy a *really fast* disk array and set it up as striped on a
superfast connection, like Ultra320 SCSI or fibre.  This will lower
the amount of time required to write the mysqldump output (which will
likely exceed 100 GB data size due to overhead within the file).  You
might even look at 2 disk arrays on 2 channels, striping across both
the disks in the array and across the arrays.  Pros: fairly easy to
do, not terribly expensive.  Cons: You still lock up your main
database server for backups, though possibly for less time than you do
now.

2) Buy a second physical server for MySQL and set up replication.
Then use the replication server to do your backups - provided you
never let people connect directly to it, no one will notice when it
locks up for a few hours dumping data.  Once it's done dumping,
replication will catch up on its own.  This doesn't even have to be a
very fast box, depending on your needs.  If it falls behind from time
to time that may be acceptable - depends on your needs.  Pros:
possibly less expensive than superfast arrays, no lockups of your main
server, backup server in case of primary failure.  Cons: requires
monitoring of replication, and still requires a one-time consistent
dump as a starting point for replication.

HTH,
Dan

On 7/10/06, Mark Steele <[EMAIL PROTECTED]> wrote:
> Hi folks,
>
>
>
> I've recently tried to do a database backup on a database server that
> has a fairly high concurrency rate (1000+ queries/sec) and have
noticed
> that the backup process seemed to deadlock the machine and I had to
> resort to extreme measures to get the database back up (killed the
> process and had to restart it in recovery mode).
>
>
>
> The command:
>
> mysqldump --all-databases --opt --single-transaction --master-data=1
> >dump.txt
>
>
>
> All my tables use InnoDB, and the database is about 100 gigabytes in
> size.
>
>
>
> Does anyone have any suggestions for getting consistent database
> snapshots?
>
>
>
> I tried the InnoDB binary backup tool in the past, but that lead to a
> corrupted database, and I'm not sure that it'll lead to a different
> outcome as both single-transaction and the binary backup tool use the
> same mechanism (versionnning). The documentation describes the
> single-transaction as taking a short global lock, which is the root
> cause of the deadlock I saw I believe.
>
>
>
> When the server was deadlocked, all the connections were 'waiting on
> table', and the backup process was apparently stuck on 'flushing
> tables'.
>
>
>
> Cheers,
>
>
>
> Mark Steele
> Information Systems Manager
>
> Zango
>
> E: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
> P: 514.787.4681 |  F: 514.787.4707
>
> www.zango.com <BLOCKED::http://www.zango.com>
>
> Read our blog at http://blog.zango.com
<BLOCKED::http://blog.zango.com>
>
>
>
>
>


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