Could it be a network bandwidth issue? Remember, all that data needs to
be transmitted across to the slave. If you are on a 10-megabit network,
it could be the cause. Remember, Ethernet is not exactly an efficient
protocol, and efficiency drops as network traffic increases.
A second machine might make it worse, not better.
David
Jon Drukman wrote:
Also even after we re-converted all the slave's Inno tables back to
MyISAM it *still* lagged out. Only after I disabled the
Inno engine
entirely did the problem abate.
Any ideas why? Does InnoDB use resources even if there are no
active tables using the engine?
This is most confusing. You're not using InnoDB *at all* and it was
slowing down the slave?
What InnoDB options had you set in my.cnf anyway?
[mysqld]
(replication commands omitted)
set-variable = query_cache_size=512M
set-variable = key_buffer=512M
set-variable = max_allowed_packet=4M
set-variable = table_cache=64
set-variable = sort_buffer=4M
set-variable = record_buffer=4M
set-variable = thread_cache=8
set-variable = tmp_table_size=128M
set-variable = thread_concurrency=4
set-variable = myisam_sort_buffer_size=128M
set-variable = max_connections=1800
set-variable = max_connect_errors=100000
set-variable = wait_timeout=30
set-variable = max_binlog_size=500000000
set-variable = long_query_time=1
#innodb_data_home_dir = /var/opt/mysql/innodb
#innodb_log_group_home_dir = /var/opt/mysql/innodb
log-error=db3-log
#log-slow-queries
skip-innodb
i spoke too soon - the slave still lags behind the master but the problem is
not nearly as bad as it was with InnoDB enabled. it seems like the combined
weight of replicating and serving tons of selects causes it to fall behind.
if we disable selects for a few seconds, it catches up again. we need to
add a second slave. (i've ordered two more just to be safe.)
mysql needs synchronous replication. we're going to eval the EMIC
clustering product in the next few weeks. i hope it works.
-jsd-
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