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master-slave replication in MySQL

+1 vote
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Looking for some help configuring 5.0.45 master-slave replication. Here's my scenario...

We have a heavily loaded 30gb 5.0.45 DB we need to replicate via master-slave configuration to a new, beefier server running same mysql 5.0.45, and then cutover to the new server. Due to extreme SAN congestion and a grossly overloaded master server, our DB dumps take 5.5 hours. But we cannot afford that much downtime or locking during the replication transition; we can manage 10-15 minutes, but more is very problematic.

I understand that "FLUSH TABLES WITH READ LOCK" will lock the tables for the duration of the 5.5 hour dump. Is this true?

If so, we'd like to dump/initialize/sync slave WITHOUT any locking anything the master for more than a few seconds if at all possible. Will this give us the dump we need?

 mysqldump --single-transaction --master-data --all-databases
posted Aug 28, 2013 by Sanketi Garg

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Why don't u try snapshot backups, where the lock held for less duration. Or can't u take mysql dumps during Night time when there is less bd activity
I neglected to mention these systems are both CentOS linux systems. Unfortunately, the 5.5 hour dumps are already done during the least busy  times.

Regarding snapshots, how long are snapshot locks held? These are ext4 filesystems. Assuming the lock is not held for long, what's the recommended way to do snapshots on ext4?

1 Answer

+1 vote

If u have LVM's then lock is held only for the duration of taking snapshot, which would be few min, if there is very less activity on the db.

answer Aug 28, 2013 by Deepak Dasgupta
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We have replication set-up, where we cater to huge amounts of data. Since quite some time, we have been facing issues wherein the slave lags behind master quite a lot.

So, yesterday we were able to setup parallel replication, by incorporating the following changes ::

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b) Set up the "slave-parallel-workers" parameter.

The above seems to work functionally fine, but we have one doubt/query about the scalability of this solution.

First, I will jot down the flow as far as I understand (please correct if wrong) ::

"Even in parallel-replication scenario, the master writes all the binlog (combined for all databases) in just one file, which then gets passed onto the slave as single-file itself. Thereafter, all the replication commands (combined for all databases) are written sequentially onto one slave-relay file.

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So far, so good. However, what would happen if the slave-relay file contains the following ::

db1-statement-1 (short-running)
db2-statement-1 (very, very long-running)
db2-statement-2 (short-running)
db1-statement-2 (short-running)
db1-statement-3 (short-running)

We will be grateful if someone could please clarify, as to how the above statements will be managed among the Manager and the Worker-Threads (let's say there is just one worker-thread-per-db) ?

In particular, does the Manager thread creates internal slave-relay-log-files, one for per database-statements?

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I have been asked to set up multiple database replication which I have done before for simple cases however there are some nuances with this instance that add some complexity and I'd like to hear your collective expertise on this proposed scenario:-

1) Single master database
2) n (probably 3 to start with) number of slave databases
3) All but 5 tables (123 tables in total) are to be replicated from the master to all the slaves
4) 3 tables from the slaves are to be replicated back to the master

It is mainly item 4) that concerns me - the primary ID's are almost certain to collide unless I seed the auto increment ID to partition the IDs into separate ranges or does MySQL handle this issue?
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We currently have a problem with a master slave setup running mysql 5.0.

This is one of our legacy servers which are in the planning to be upgraded, however in order for this to be done the replication needs to be up and running.

The problem we have currently however is that the binary logs on the master was moved to a seperate partition due to disc space restrictions.

A new binlog file called mysql-bin.1 was created and everything seemed to work fine.

However, the moment the file reached the file size of 100Mb, it does not go on to create a new binlog file called mysql-bin.2 and the replication fails stating that it is unable to read the binary log file.

Thus far we have done a flush logs and reset master , but the same problem occurs, where it creates mysql-bin.1 and the moment it reaches it's max size and suppose to create a new file, it stops and
does not create the new one.

I really hope this makes sense, and that someone can perhaps point us in the correct direction.


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