Re: Binary Logs and Transactions (with InnoDB and MyISAM)

[Chris Nolan]

Basically, only error-free statements are replicated.to the slave, thus 
ensuring that constraints are satisfied.

Regards,

Chris

David Griffiths wrote:

Thanks for the reply.

So InnoDB (and even MyISAM) use transactions (expected with InnoDB) and
slaves track their position in the binary log files as they are reading them
in so as not to violate any constraints?
David
----- Original Message -----
From: "Chris Nolan" <[EMAIL PROTECTED]>
To: "David Griffiths" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Friday, February 13, 2004 5:46 PM
Subject: Re: Binary Logs and Transactions (with InnoDB and MyISAM)
 

Hi David,

David Griffiths wrote:

From reading the docs, a binary log is an efficient representation of all
   

data-modifying SQL that is run on the master database. I was unable to
figure out what happens if a slave is interrupted while in the middle of
processing a binary log.
When a binary log is applied to a slave database, what happens if the
machine or database dies half way through the log?


     

Basically, the slave will try to "catch up" when it restarts.

   

For example, with InnoDB, say the following statements are run and stored
     

in
 

the binary log:

---------------------------
1) INSERT INTO table_a (column_a, column_b, ...) VALUES (...);
2) COMMIT;

3) UPDATE table_a SET column_b = 'some_value' WHERE column_c =
'something_else';
4) COMMIT;
-----------------------------
The slave-machine (also using InnoDB tables) start processing the binary
log. Statement 1 and 2 are processed, but it dies before Statement 3
     

(UPDATE
 

table_a...) is executed.

     

If I recall correctly, the binary log uses transactions as it's basic
units. I'm not even sure if the slave will see statement 3 before
statement 4, but I know it definitely will not act on it in any way.
   

If you restart the slave, would it start the binary log back at the
beginning, or is the offset inside the file stored in the database so
     

that
 

the slave database starts at Statement 3? Or would the whole log be
re-processed (potentially causing problems with inserting rows with
     

unique
 

keys)?

     

The slave won't try to reperform actions that are already processed. You
can relax regarding unique attributes.
   

How does this work with MyISAM?

     

In essentially the same way. As each statement is basically bound with
BEGIN and COMMIT statements, each statement is processed by the slave
after it successfully completes on the master.
   

Thanks,
David


     

Regards,

Chris
   



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