Parallel apply is enabled using the
svc-parallelization-type and
channels options of
tpm. The parallelization type defaults to
none which is to say
that parallel apply is disabled. You should set it to
disk. The
channels option sets the the number of
channels (i.e., threads) you propose to use for applying data. Here is a
code example of a MySQL Applier installation with parallel apply enabled. The
Replica will apply transactions using 30 channels.
shell> vi /etc/tungsten/tungsten.ini[defaults]
install-directory=/opt/continuent
user=tungsten
mysql-allow-intensive-checks=true
profile-script=~/.bash_profile
application-port=3306
application-user=app_user
application-password=secret
replication-port=13306
replication-user=tungsten
replication-password=secret
svc-parallelization-type=disk
connector-smartscale=false # parallel apply and smartscale are not compatible
channels=10
rest-api-admin-user=apiuser
rest-api-admin-pass=secret
[alpha]
master=host1
members=host1,host2,host3
connectors=host1,host2,host3
topology=clusteredConfiguration group defaults
Configuration group alpha
If the installation process fails, check the output of the
/tmp/tungsten-configure.log file for
more information about the root cause.
There are several additional options that default to reasonable values. You may wish to change them in special cases.
buffer-size — Sets the
replicator block commit size, which is the number of transactions to
commit at once on Replicas. Values up to 100 are normally fine.
native-slave-takeover — Used
to allow Tungsten to take over from native MySQL replication and
parallelize it. See here for more.
You can check the number of active channels on a Replica by looking at the "channels" property once the replicator restarts.
Replica shell> trepctl -service alpha status| grep channels
channels : 10The channel count for a Primary will ALWAYS be 1 because extraction is single-threaded:
Primary shell> trepctl -service alpha status| grep channels
channels : 1Enabling parallel apply will dramatically increase the number of connections to the database server.
Typically the calculation on a Replica would be: Connections = Channel_Count x Sevice_Count x 2, so for a 4-way Composite Composite Active/Active topology with 30 channels there would be 30 x 4 x 2 = 240 connections required for the replicator alone, not counting application traffic.
You may display the currently used number of connections in MySQL:
mysql> SHOW STATUS LIKE 'max_used_connections';
+----------------------+-------+
| Variable_name | Value |
+----------------------+-------+
| Max_used_connections | 190 |
+----------------------+-------+
1 row in set (0.00 sec)Below are suggestions for how to change the maximum connections setting in MySQL both for the running instance as well as at startup:
mysql> SET GLOBAL max_connections = 512;
mysql> SHOW VARIABLES LIKE 'max_connections';
+-----------------+-------+
| Variable_name | Value |
+-----------------+-------+
| max_connections | 512 |
+-----------------+-------+
1 row in set (0.00 sec)
shell> vi /etc/my.cnf
#max_connections = 151
max_connections = 512