It seems to me that once the read lock is acquired, only the binary log coordinates are read. Soon after binary log coordinates are read, lock is released. Is there anything else that happens here?
It means that after lock is released, dump is made while the read and write activity is going on. This dump then, would be inconsistent. So, to make this dump a consistent one when restoring it, binary log will be applied starting from the binary log coordinates that has been read earlier. This is what I understand. Please correct me if my understanding is wrong. Best Regards, Geetanjali Mehra Senior Oracle and MySQL DBA Corporate Consultant and Database Security Specialist On Tue, Oct 7, 2014 at 6:22 AM, shawn l.green <shawn.l.gr...@oracle.com> wrote: > Hello Geetanjali, > > On 9/23/2014 7:14 AM, geetanjali mehra wrote: > >> Can anybody please mention the internals that works when we use mysqldump >> as follows: >> >> >> *mysqldump --single-transaction --all-databases > backup_sunday_1_PM.sql* >> >> MySQL manual says: >> >> This backup operation acquires a global read lock on all tables at the >> beginning of the dump (using *FLUSH TABLES WITH READ LOCK >> <http://dev.mysql.com/doc/refman/5.6/en/flush.html>*). As soon as this >> lock >> has been acquired, the binary log coordinates are read and the lock is >> released. If long updating statements are running when the FLUSH >> <http://dev.mysql.com/doc/refman/5.6/en/flush.html> statement is issued, >> the backup operation may stall until those statements finish. After that, >> the dump becomes lock-free and does not disturb reads and writes on the >> tables. >> >> Can anyone explain it more? Please. >> >> > Which part would you like to address first? > > I have a feeling it's more about how FLUSH TABLES WITH READ LOCK works but > I want to be certain before answering. > > Yours, > -- > Shawn Green > MySQL Senior Principal Technical Support Engineer > Oracle USA, Inc. - Hardware and Software, Engineered to Work Together. > Office: Blountville, TN > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/mysql > >
