Re: SOLVED: Problem with *very* slow replication, FreeBSD 6.2

[Baron Schwartz]

Christopher E. Brown wrote:
> On Sat, 3 Nov 2007, bob b wrote:
> So, a slave is down for 8hrs.  It comes online and pulls the binlog in 
> 120 seconds.  The "seconds behind master" does not reflect 8hrs, but how 
> many seconds (at current processing rate) before the slave finishes the 
> relay logs.
> 
> 
> The "seconds behind master" value is really "seconds until currency with 
> the relay logs" and should prolly be documented as such.

This is incorrect.  In most circumstances, it's basically the difference 
between the timestamp of the binlog event the SQL thread is currently 
processing, and the master's current timestamp (as fetched by the I/O 
thread).  So it really is what it sounds like: the seconds behind the 
master.  If it says 100, it means the slave is processing an event that 
took place 100 seconds ago on the master.

You can read the source code in show_master_info() in sql/slave.cc.

Baron