Document gvwstate.dat

[ronin13]

Purpose and (internal) use of this file is not documented.

[ayurchen]

Yan, could you please describe it in comments here.

[dirtysalt]

gvwstate.dat file is for PC recovery feature, related to #10 #65 . This file is created once primary component is formed or changed, so you can get the latest primary component this node was in. And this file is deleted when the node is shutdown gracefully.

A typical gvwstate.dat is like this

my_uuid: d3124bc8-1605-11e4-aa3d-ab44303c044a
#vwbeg
view_id: 3 0dae1307-1606-11e4-aa94-5255b1455aa0 12
bootstrap: 0
member: 0dae1307-1606-11e4-aa94-5255b1455aa0 1
member: 47bbe2e2-1606-11e4-8593-2a6d8335bc79 1
member: d3124bc8-1605-11e4-aa3d-ab44303c044a 1
#vwend

It can be split into two parts:

1. node information. It only has node's UUID.
2. view information.

View information starts with #vwbeg and ends with vwend. It has several parts:

1. view_id: [view_type] [view_uuid] [view_seq]. # view_type is always 3 which means primary view. view_uuid and view_seq identifies a unique view, which could be perceived as identifier of this primary component.
2. bootstrap: [bootstarp_or_not]. # It could be 0 or 1, but does not affect pc recovery process now.
3. member: [node's uuid] [node's segment]. # it represents all nodes in this primary component.

[jayjanssen]

Yan,
This is helpful. I’m wondering if this file can be used in a hacky way to force a new cluster to form in odd circumstances like automated provisioning systems.

Let’s say I have a new 3 node cluster that I want to bootstrap, but I can’t guarantee which node will ‘start’ first. Is there a way to tinker with this file to instruct the nodes to, for example, form a cluster when 3 (new, with unknown uuids) appear in the non-primary group?

Can I somehow know the UUID of a given node in advance of starting the node? Can I somehow override it?

On Jul 27, 2014, at 11:44 PM, yan.zhang notifications@github.com wrote:

gvwstate.dat file is for PC recovery feature, related to #10 #65 . This file is created once primary component is formed or changed, so you can get the latest primary component this node was in. And this file is deleted when the node is shutdown gracefully.

A typical gvwstate.dat is like this

my_uuid: d3124bc8-1605-11e4-aa3d-ab44303c044a
#vwbeg
view_id: 3 0dae1307-1606-11e4-aa94-5255b1455aa0 12
bootstrap: 0
member: 0dae1307-1606-11e4-aa94-5255b1455aa0 1
member: 47bbe2e2-1606-11e4-8593-2a6d8335bc79 1
member: d3124bc8-1605-11e4-aa3d-ab44303c044a 1
#vwend
It can be split into two parts:

1. node information. It only has node's UUID.
2. view information.(primary component information).

View information starts with #vwbeg and ends with vwend. It has several parts:

1. view_id: [view_type] [view_uuid] [view_seq]. # view_type is always 3 which means primary view. view_uuid and view_seq identifies a unique view of this primary component.
2. bootstrap: [bootstarp_or_not]. # It could be 0 or 1, but does not affect pc recovery process now.
3. member: [node's uuid] [node's segment]. # it represents all nodes in this primary component.

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Jay Janssen
http://about.me/jay.janssen

[dirtysalt]

UUID of a node is generated randomly when the node starts, so you don't know what is the UUID of a node before starting it. But with pc recovery feature(it's on by default to 3.6), if there is gvwstate.dat file in mysql data directory, galera will read this file and use content of field 'my_uuid' as UUID.

For safety, you'd better not to to do some hack on this file, because it may makes some weird cases. But to the case as you mentioned, I think yes. You can tinker with this file to instruct these three nodes to form a primary component automatically. Here are the steps:

Assume there are three nodes A,B,C. You could use tools to generate three UUIDs Ua, Ub, Uc. And in lexicographic order, Ua < Ub < Uc.

So gvwstate.dat of node A could be like this

my_uuid: Ua
#vwbeg
view_id: 3 Ua 100[whatever positive number]
bootstrap: 0
member: Ua 0[segment of node A]
member: Ub 0
member: Uc 0
#vwend

gvwstate.dat of node B could be like this

my_uuid: Ub
#vwbeg
view_id: 3 Ua 100[whatever positive number]
bootstrap: 0
member: Ua 0[segment of node A]
member: Ub 0
member: Uc 0
#vwend

gvwstate.dat of node C could be like this

my_uuid: Uc
#vwbeg
view_id: 3 Ua 100[whatever positive number]
bootstrap: 0
member: Ua 0[segment of node A]
member: Ub 0
member: Uc 0
#vwend

Start all three nodes without bootstrap flag and they will form a primary component automatically.

[temeo]

Documentation and open issues moved to https://github.com/codership/documentation/.