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From:Rick James Date:April 23 2008 6:32pm
Subject:RE: innodb replication
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Will FLUSH wait for any transactions to COMMIT (or ROLLBACK)?

> -----Original Message-----
> From: Jeremy Cole [mailto:jeremy.cole@stripped] On 
> Behalf Of Jeremy Cole
> Sent: Wednesday, April 23, 2008 11:20 AM
> To: Rick James
> Cc: Eric Bergen; augusto@stripped; replication@stripped
> Subject: Re: innodb replication
> 
> Hi Rick,
> 
> Sure, but why not?  Both states (pre-transaction and 
> post-transaction) 
> are valid, consistent states.  It's exactly as though you had 
> taken the 
> snapshot a bit earlier than you actually did.
> 
> In fact, the only reason to use FLUSH TABLES WITH READ LOCK in this 
> context is so that you can get the binary log positions 
> aligned with it. 
>   Strictly, you don't need it.
> 
> Regards,
> 
> Jeremy
> 
> Rick James wrote:
> > Consistent state, yes.  But what about mid-transaction?  
> Might it be that the snapshot will have half the transaction 
> and have to ROLLBACK, while the live machine (after UNLOCK) 
> will COMMIT the transaction? 
> > 
> >> -----Original Message-----
> >> From: eric.bergen@stripped 
> >> [mailto:eric.bergen@stripped] On Behalf Of Eric Bergen
> >> Sent: Tuesday, April 22, 2008 7:12 PM
> >> To: augusto@stripped
> >> Cc: replication@stripped
> >> Subject: Re: innodb replication
> >>
> >> Innodb always keeps it's files in a consistent state on disk. Power
> >> failure and snapshots of the system won't result in a corrupt data
> >> file. You can find more details on how innodb achieves this here:
> >> http://www.mysqlperformanceblog.com/2006/08/04/innodb-double-write/
> >>
> >> More replies inline.
> >>
> >> On Tue, Apr 22, 2008 at 5:22 PM, Augusto Bott 
> >> <augusto@stripped> wrote:
> >>> Hi Mark, Eric!
> >>>
> >>>  The last comments on this thread got me thinking about all those
> >>>  backup chalenges... since a FLUSH TABLES won't stop 
> internal InnoDB
> >>>  threads from working and changing the datafiles in the 
> >> background, how
> >>>  can we be absolutely sure that a filesystem snapshot will 
> >> be actually
> >>>  consistent when it's taken? What if when we're taking that 
> >> snapshot in
> >>>  the precise moment when InnoDB threads are working and 
> >> modifying data?
> >>>  How can we be sure that the snapshot will not be taken on 
> >> the precise
> >>>  moment there's a write in place?
> >>>
> >>>  I must acknowledge under this scenario, taking a 
> 'instant' snapshot
> >>>  from the filesystem will greatly reduce the probability of 
> >> corruption
> >>>  but... any ideas on how to get it 100% safe? (hm... 
> >> perhaps we should
> >>>  discuss this on internals@ ?)
> >> See the notes above on why the snapshot is guaranteed not to 
> >> be corrupt.
> >>
> >>>  On the other hand, we're talking about warm backups on a 
> >> slave, right?
> >>>  So... what if we stop replication, issued a flush tables, 
> >> waited for a
> >>>  moment until IO operations stop, and then start copying 
> >> the datafiles
> >>>  or taking that snapshot?
> >> You may as well just shutdown the slave. It's safer than trying to
> >> determine if innodb isn't going to write something.
> >>
> >>>  Anyway... I don't recall having experienced corruption 
> >> when restoring
> >>>  from a warm backup (ever), but that may be that I just 
> >> "got lucky" or
> >>>  didn't look into the data deep enough to actually find 
> any problems
> >>>  :-)
> >>>
> >>>  Cheers!
> >>>
> >>>  --
> >>>  Augusto Bott
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>  On Mon, Apr 21, 2008 at 8:27 PM, Mark Callaghan 
> >> <mcallaghan@stripped> wrote:
> >>>  >
> >>>  >
> >>>  >
> >>>  > On Mon, Apr 21, 2008 at 5:14 PM, Augusto Bott 
> >> <augusto@stripped> wrote:
> >>>  > > Hi Rick, Eric, Marcus!
> >>>  > >
> >>>  > > I must correct some of the things that have been said 
> >> on this thread.
> >>>  > > I'm not commenting on rumors, just the facts from the 
> >> documentation
> >>>  > > (and a few years of experience with MySQL) :-)
> >>>  > >
> >>>  > > If you're running your MySQL server with
> >>>  > > innodb_flush_log_at_trx_commit=1 (that's the default), 
> >> issuing FLUSH
> >>>  > > TABLES WITH READ LOCK will indeed prevent modification to
> the
> >>>  > > datafiles while the global read lock is held since all 
> >> committed
> >>>  > > transactions (so far) will be for sure on disk. The 
> >> global read lock
> >>>  > > stays in place until UNLOCK TABLES is issued or until 
> >> that connection
> >>>  > > is closed/timed out. This makes it safe to copy the 
> >> datafiles for a
> >>>  > > backup - the result is indeed a consistent backup.
> >>>  >
> >>>  > FLUSH TABLES WITH READ LOCK should allow for a snapshot 
> >> (LVM, ZFS) to be
> >>>  > used to copy all files -- as long as they are on the 
> >> same filesystem. But I
> >>>  > do not think it is safe to copy InnoDB files without a 
> >> snapshot as the
> >>>  > background IO threads (purge, insert buffer, page 
> >> writer) can do IO during
> >>>  > FLUSH TABLES WITH READ LOCK. I have not seen any code 
> >> that makes the InnoDB
> >>>  > background IO threads wait when there is a global read lock.
> >>>  >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > > This operation can be called a 'warm backup'. A hot 
> >> backup is what
> >>>  > > "InnoDB Hot Backup" does: it does not lock anything 
> >> while it's running
> >>>  > > and transactions can start and commit while it's 
> >> running (the tool
> >>>  > > requires a brief global read lock at the beginning, 
> >> when the backup is
> >>>  > > starting) and takes a full consistent backup (you must 
> >> license it to
> >>>  > > use it). A cold backup would be shutting down MySQL, 
> >> copying the
> >>>  > > datafiles and firing it up again (also a safe move).
> >>>  > >
> >>>  > > The "caveat" when you make a warm backup is that the 
> >> datafiles will be
> >>>  > > marked 'dirty' and on the next startup, the logs will 
> >> be replayed to
> >>>  > > bring the database to a consistent point, since it 
> >> "wasn't closed
> >>>  > > properly" (to the very same point when you issued the 
> >> FLUSH TABLES
> >>>  > > WITH READ LOCK statement).
> >>>  > >
> >>>  > > --
> >>>  > > Augusto Bott
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > > On Sun, Apr 20, 2008 at 5:46 PM, Eric Bergen 
> >> <ebergen@stripped>
> >>>  > wrote:
> >>>  > > > Hi,
> >>>  > > >
> >>>  > > >  The flush tables with read lock issue has to do 
> >> with copying the files
> >>>  > > >  off the disk, not with using mysqldump's sql. The 
> >> issue is that flush
> >>>  > > >  tables with read lock is enough to prevent clients 
> >> from modifying
> >>>  > > >  innodb but it doesn't make innodb "hold still" . It 
> >> still has
> >>>  > > >  background threads modifying the data files. If you 
> >> did a flush tables
> >>>  > > >  with read lock; then copied the data files they 
> >> will almost certainly
> >>>  > > >  be corrupted because different parts of the files 
> >> are copied at
> >>>  > > >  different times.
> >>>  > > >
> >>>  > > >  If you use mysqldump --master-data it will turn on 
> >> --lock-all-tables
> >>>  > > >  automatically giving you a consistent snapshot 
> >> across all storage
> >>>  > > >  engines. The downside of this is that mysqldump has 
> >> to hold a read
> >>>  > > >  lock the entire time it's dumping data. If you're 
> >> only using innodb
> >>>  > > >  you can specify --master-data --single-transaction 
> >> mysqldump will
> >>>  > > >  issue a flush tables with read lock long enough to 
> >> copy the master
> >>>  > > >  data and start a transaction. With a transaction 
> >> started innodb will
> >>>  > > >  only return rows that were committed before the 
> >> transaction was
> >>>  > > >  started. Other transactions can proceed and innodb 
> >> won't see the rows.
> >>>  > > >
> >>>  > > >
> >>>  > > >
> >>>  > > >  On Fri, Apr 18, 2008 at 4:14 PM, Rick James 
> >> <rjames@stripped>
> >>>  > wrote:
> >>>  > > >  > Rumor has it that InnoDB used to still have some 
> >> things in RAM after
> >>>  > the  "FLUSH TABLES WITH READ LOCK", thereby disallowing 
> >> it as a safe way to
> >>>  > dump InnoDB tables.  Another rumor has it that that has 
> >> been fixed.  [Sorry
> >>>  > for lack of details; hope someone will respond with details.]
> >>>  > > >  >
> >>>  > > >  >  I prefer to stop mysql, copy the necessary 
> >> directories, then restart
> >>>  > mysql.  An improvement on that is to use Snapshots (eg 
> >> LVM on Linux).  They
> >>>  > make that extremely fast, hence very practical.  (The 
> >> copy can be done from
> >>>  > the snapshot _after_ restarting mysql.)
> >>>  > > >  >
> >>>  > > >  >
> >>>  > > >  >
> >>>  > > >  >  > -----Original Message-----
> >>>  > > >  >  > From: Marcus Bointon 
> [mailto:marcus@stripped]
> >>>  > > >  >  > Sent: Friday, April 18, 2008 2:42 AM
> >>>  > > >  >  > To: replication@stripped
> >>>  > > >  >  > Subject: Re: innodb replication
> >>>  > > >  >  >
> >>>  > > >  >  > On 18 Apr 2008, at 10:27, Ed W wrote:
> >>>  > > >  >  >
> >>>  > > >  >  > >> I´m going to set up a innodb
> database 
> >> replication, and I
> >>>  > > >  >  > have some
> >>>  > > >  >  > >> doubts
> >>>  > > >  >  > >> about the backing up the master
> database step.
> >>>  > > >  >  > >>
> >>>  > > >  >  > >> Normally, I do a "FLUSH TABLES WITH
> READ 
> >> LOCK", backup the data
> >>>  > > >  >  > >> files (or
> >>>  > > >  >  > >> use mysqldump), get the current log
> 
> >> coordinates with "SHOW
> >>>  > MASTER
> >>>  > > >  >  > >> STATUS"
> >>>  > > >  >  > >> and unlock the tables. Using
> exactly the 
> >> same steps work for
> >>>  > innodb
> >>>  > > >  >  > >> databases?
> >>>  > > >  >  > >>
> >>>  > > >  >  > >> According to some texts, it seems
> not, but 
> >> I haven´t found
> >>>  > > >  >  > a clear
> >>>  > > >  >  > >> cookbook.
> >>>  > > >  >  > >>
> >>>  > > >  >  > >>
> >>>  > > >  >  > >> Just doing a "mysqldump
> --master-data 
> >> --single-transaction" is
> >>>  > > >  >  > >> enough to
> >>>  > > >  >  > >> replace the above steps?
> >>>  > > >  >  > >>
> >>>  > > >  >  > >>
> >>>  > > >  >  > >
> >>>  > > >  >  > > How would you put these two things
> together 
> >> in the case of
> >>>  > > >  >  > a server
> >>>  > > >  >  > > using mixed database table types for a
> clean 
> >> backup that
> >>>  > > >  >  > can be used
> >>>  > > >  >  > > to restart synchronisation?
> >>>  > > >  >  >
> >>>  > > >  >  >
> >>>  > > >  >  > You can't. Only InnoDB supports 
> >> single-transaction, so though
> >>>  > > >  >  > it would
> >>>  > > >  >  > still generate a dump file for other table 
> >> types, you'd have no
> >>>  > > >  >  > assurance that they are clean because writes
> could be
> >>>  > > >  >  > happening as you
> >>>  > > >  >  > do it. This is one of the advantages of
> using innodb.
> >>>  > > >  >  >
> >>>  > > >  >  > You can of course do separate dumps for
> other 
> >> DBs, and because
> >>>  > that
> >>>  > > >  >  > wouldn't need to include the innodb tables,
> it 
> >> would at least
> >>>  > reduce
> >>>  > > >  >  > the time that your tables are locked.
> >>>  > > >  >  >
> >>>  > > >  >  > You could also look at maatkit's parallel 
> >> dump/load scripts.
> >>>  > > >  >  >
> >>>  > > >  >  > Marcus
> >>>  > > >  >  > --
> >>>  > > >  >  > Marcus Bointon
> >>>  > > >  >  > Synchromedia Limited: Creators of 
> >> http://www.smartmessages.net/
> >>>  > > >  >  > UK resellers of info@hand CRM solutions
> >>>  > > >  >  > marcus@stripped | 
> >> http://www.synchromedia.co.uk/
> >>>  > > >  >  >
> >>>  > > >  >  >
> >>>  > > >  >  >
> >>>  > > >  >  > --
> >>>  > > >  >  > MySQL Replication Mailing List
> >>>  > > >  >  > For list archives:
> http://lists.mysql.com/replication
> >>>  > > >  >  > To unsubscribe:
> >>>  > > >  >  > 
> >> http://lists.mysql.com/replication?unsub=1
> >>>  > > >  >
> >>>  > > >  >
> >>>  > > >  > >
> >>>  > > >  >  >
> >>>  > > >  >
> >>>  > > >  >  --
> >>>  > > >  >  MySQL Replication Mailing List
> >>>  > > >  >  For list archives:
> http://lists.mysql.com/replication
> >>>  > > >  >  To unsubscribe:
> >>>  > http://lists.mysql.com/replication?unsub=1
> >>>  > > >  >
> >>>  > > >  >
> >>>  > > >
> >>>  > > >
> >>>  > > >
> >>>  > > >  --
> >>>  > > >  Eric Bergen
> >>>  > > >  eric.bergen@stripped
> >>>  > > >  http://www.provenscaling.com
> >>>  > > >
> >>>  > > >
> >>>  > > >
> >>>  > > >  --
> >>>  > > >  MySQL Replication Mailing List
> >>>  > > >  For list archives: http://lists.mysql.com/replication
> >>>  > > >  To unsubscribe:
> >>>  > http://lists.mysql.com/replication?unsub=1
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > >
> >>>  > > >
> >>>  > > >
> >>>  > >
> >>>  > > --
> >>>  > > MySQL Replication Mailing List
> >>>  > > For list archives: http://lists.mysql.com/replication
> >>>  > > To unsubscribe:
> >>>  > http://lists.mysql.com/replication?unsub=1
> >>>  > >
> >>>  > >
> >>>  >
> >>>  >
> >>>  >
> >>>  > --
> >>>  > Mark Callaghan
> >>>  > mcallaghan@stripped
> >>>
> >>>  --
> >>>
> >>> MySQL Replication Mailing List
> >>>  For list archives: http://lists.mysql.com/replication
> >>>  To unsubscribe:    
> >> http://lists.mysql.com/replication?unsub=1
> >>>
> >>
> >>
> >> -- 
> >> high performance mysql consulting.
> >> http://provenscaling.com
> >>
> >> -- 
> >> MySQL Replication Mailing List
> >> For list archives: http://lists.mysql.com/replication
> >> To unsubscribe:    
> >> http://lists.mysql.com/replication?unsub=1
> >>
> >>
> > 
> 
> -- 
> high performance mysql consulting
> www.provenscaling.com
> 
Thread
innodb replicationEdson Noboru Yamada23 Mar
  • Re: innodb replicationMarcus Bointon24 Mar
  • Re: innodb replicationEd W18 Apr
    • Re: innodb replicationMarcus Bointon18 Apr
      • Re: innodb replicationEd W18 Apr
        • Re: innodb replicationMarcus Bointon18 Apr
      • RE: innodb replicationRick James19 Apr
        • Re: innodb replicationEric Bergen20 Apr
          • Re: innodb replicationAugusto Bott22 Apr
            • Re: innodb replicationMark Callaghan22 Apr
              • Re: innodb replicationAugusto Bott22 Apr
                • Re: innodb replicationEric Bergen22 Apr
              • Re: innodb replicationAugusto Bott23 Apr
                • Re: innodb replicationEric Bergen23 Apr
                  • RE: innodb replicationRick James23 Apr
                    • Re: innodb replicationMarcus Bointon23 Apr
                    • Re: innodb replicationJeremy Cole23 Apr
                      • RE: innodb replicationRick James23 Apr
                        • Re: innodb replicationJeremy Cole23 Apr
                          • RE: innodb replicationRick James23 Apr
                            • Re: innodb replicationMarcus Bointon23 Apr
                              • Re: innodb replicationEric Bergen24 Apr
                                • Re: innodb replicationMoon's Father21 May