Tomas Eduardo Fernandez Lobbe created SOLR-14306:
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Summary: Refactor coordination code into separate module and
evaluate using Curator
Key: SOLR-14306
URL: https://issues.apache.org/jira/browse/SOLR-14306
Project: Solr
Issue Type: Improvement
Security Level: Public (Default Security Level. Issues are Public)
Components: SolrCloud
Reporter: Tomas Eduardo Fernandez Lobbe
This Jira issue is to discuss two changes that unfortunately are difficult to
address separately
# Separate all ZooKeeper coordination logic into it’s own module, that can be
tested in isolation
# Evaluate using Apache Curator for coordination instead of our own logic.
I drafted a
[SIP|https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=148640472],
but this is very much WIP, I’d like to hear opinions before I spend too much
time on something people hates.
>From the initial draft of the SIP:
{quote}The main goal of this change is to allow better testing of the different
ZooKeeper interactions related to coordination (leader election, queues, etc).
There are already some abstractions in place for lower level operations
(set-data, get-data, etc, see DistribStateManager), so the idea is to have a
new, related abstraction named CoordinationManager, where we could have some
higher level coordination-related classes, like LeaderRunner (Overseer),
LeaderLatch (for shard leaders), etc.
Curator comes into place because, in
order to refactor the existing code into these new abstractions, we’d have to
rework much of it, so we could instead consider using Curator, a library that
was mentioned in the past many times. While I don’t think this is required, It
would make this transition and our code simpler (from what I could see,
however, input from people with more Curator experience would be greatly
appreciated).
While it would be out of the scope of this change, If the
abstractions/interfaces are correctly designed, this could lead to, in the
future, be able to use something other than ZooKeeper for coordination, either
etcd or maybe even some in-memory replacement for tests.
{quote}
There are still many open questions, and many questions I still don’t know
we’ll have, but please, let me know if you have any early feedback, specially
if you’ve worked with Curator in the past.
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