Native persistence

[Humphrey <hm...@gmail.com>]

Hello,

I'm trying something out in minikube/minishift with native persistence and
scaling.

I created persistent volume and a persistence volume claim and have the
IGNITE_HOME variable pointed to it. They are bounded correctly.

I can see it's making a directory ${IGNITE_HOME}/work/db with underneath a
folder corresponding to the node. 
Let's say the directory it makes is called 


- When I shutdown and restart I see that it claims the same volume and my
data is restored.

I also see it doesn't create new directory so it's using the same one
(replica1).

When I then scale up to 4 replica's I see that 3 other directories are
created for each new node:


Then I scale back down to 2 replica's. 

What will happen if at a later point I want to scale back up to 4 replica's?
Ignite doesn't make new directories, but reuses the existing ones.
- So what will happen with the data it finds in the existing directory (and
probably are old), how does it handle this?

- What happens in the situation that I shutdown my cluster and restart it
with 2 replica's. How does ignite know which two of the four directories to
re-use?

Humphrey




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Re: Native persistence

[ezhuravlev <e....@gmail.com>]

Hi Humphrey,

>What will happen if at a later point I want to scale back up to 4
replica's? 
>- So what will happen with the data it finds in the existing directory (and 
probably are old), how does it handle this? 

It depends on the time when the node was down. If it was a short period of
time and it's possible to apply delta rebalance - the current partitions
will be updated to the last version. Otherwise, old partitions will be
dropped and full rebalance will happen, like for new nodes. The possibility
of applying delta rebalance depends on configured walHistorySize.

>- What happens in the situation that I shutdown my cluster and restart it 
with 2 replica's. How does ignite know which two of the four directories to 
re-use? 

By default, folder name contains IP and port of node related to this
persistent store's data. So, the newly started node will choose a folder for
the IP and host that it has. Also, it's possible to set consistentId for the
node, in this case, the node will choose folder with the name related to
it's consistentId. 

Evgenii



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