Galera parametrs

MySQL & MariaDB Percona XtraDB Cluster 8.x
1

Hi,

Concerning these two parameters in Galera configuration, evs.keepalive_period and evs.inactive_check_period
Looking in Galera documentation the default values for both is PT1S
Also, the relation between the two parameters is
evs.keepalive_period <= evs.inactive_check_period

But in percona xtradb documentation, the default values are
evs.keepalive_period = PT1S
evs.inactive_check_period = PT0.5S

Then the above relation is not satisfied .

Please, can you explain why for xtdadb , the defaul vakues are different and the relation is not satisfied ?

Also, il seems that ffor checking peer connectivity, each node in galera cluster uses gmcast.peer_timeout

Can you explain how each node check the reachabilty of the other nodes. I mean which parameter is used ( gmcast.peer_timeout or evs.keepalive_period ) ?

Thanks.

2

Hello @stofa.kenida

evs.keepalive_period - defines how often node sends “ping” to other nodes
default: 1s
min: 0.1s
max: evs.susspect_timeout/3 + 1

evs.inactive_check_period - defines how often the node checks for “pings” from other nodes
default: 0.5s
min: 0s
max: evs.susspect_timeout/2 + 1

evs.inactive_timeout - defines when node is considered dead and evicted
default: 15s

All default values are the same as for Galera from Codership. It seems that upstream Galera documentation is not accurate.

Also, the relation between the two parameters is
evs.keepalive_period <= evs.inactive_check_period

Why? I think there is no such relation.

gmcast.peer_timeout - defines when Galrea activates relaying protocol between nodes

1 Like
3

Hi Kamil

The relation between the two parameters is found here

As you can see, it s reported that
evs-keepalive-period) <= evs.inactive_check_period

Also, for gmcast.peer_timeout , what do you mean by "relaying protocol " ?
There is no documentation describing how it works.
I can guess it is used by Galera to fetch info about one node by contacting other nodes.

4

Please consider a three-node cluster. In normal circumstances, each node sees all other nodes. Now imagine that communication between nodes 1 and 3 is blocked for any reason. In such a case, Galera activates a low-level protocol that allows node 1 to communicate with node 3 via node 2. This is a relaying protocol.