tree f7418eb32e14971ea5e0610a34eaac95631c0d60
parent 92b792a78fed2adeec0dc47686d23a392b9dd612
author Luca Milanesio <luca.milanesio@gmail.com> 1588608852 +0100
committer Luca Milanesio <luca.milanesio@gmail.com> 1591055818 +0000

Enable rolling upgrade to next versions

Gerrit version N and N+1 (e.g. Gerrit v3.1 is N, v3.2 is N+1)
have typically a semi-compatible schema which enables the ability
to perform a live-upgrade to the new release without the need of
a general outage.

Document how to enable rolling upgrade mode and make the schema
version check more flexible so that two versions can
share the same repositories over NFS.

Test plan:

1. Install Gerrit version N on two nodes sharing the repositories
   over NFS.
2. Set gerrit.experimentalRollingUpgrade to true
3. Upgrade one of the two nodes to version N+1
4. Both nodes should be able to stop/start without issues
5. Both nodes should be able to serve read/writes without issues
6. Upgrade the other node then confirm as above.

Change-Id: I8ceb352365da2eb553d82495c9635eb034e57352