[
https://issues.apache.org/jira/browse/SOLR-6512?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14142192#comment-14142192
]
Erick Erickson commented on SOLR-6512:
--------------------------------------
[[email protected]] [~noble.paul]
Don't want the train to leave the station without people being on board. This
particular patch allows _arbitrary_ roles to be assigned to a replica. The
first use-case is, of course, the preferredLeader stuff, but it's not confined
to that.
So we can commit this if it's useful without having to use it for the
preferredLeader stuff at all.
> Add a collections API call to add/delete arbitrary roles to a specific replica
> ------------------------------------------------------------------------------
>
> Key: SOLR-6512
> URL: https://issues.apache.org/jira/browse/SOLR-6512
> Project: Solr
> Issue Type: Improvement
> Reporter: Erick Erickson
> Assignee: Erick Erickson
> Attachments: SOLR-6512.patch, SOLR-6512.patch
>
>
> This is a sub-task for SOLR-6491, but seems generally useful.
> Since this is in support of the "preferredLeader" functionality, I've run
> into some considerations that I wanted some feedback on how to handle.
> "preferredLeader" has the restriction that there should only be one per
> slice, so setting this for a particular node means removing the property for
> all the other replicas on the slice. Not a problem to do, my question is more
> whether this is something reasonable to enforce on an arbitrary property
> based on what that property is? Perfectly do-able, but "semantically
> challenged". Currently, this is never a node with "preferedLeader" set to
> "false", it is forcibly removed from other nodes in the slice when this
> property is assigned.
> The problem here is that there's nothing about assigning an arbitrary
> property to a node that would reasonably imply this kind of behavior. One
> could always control this with secondary flags on the command, e.g.
> "shardExclusive=true|false" for instance, perhaps with safety checks in for
> known one-per-shard properties like "preferredLeader".
> "preferredLeader" seems to fit more naturally into a "role", but currently
> ADDROLE and DELTEROLE have nothing to do with the notion of setting a role
> for a particular node relative to a collection/shard. Easy enough to add, but
> enforcing the "only one node per slice may have this role" rule there is
> similarly arbitrary and overloads the ADDROLE/DELETEROLE in a way that seems
> equally confusing. Plus, checking whether the required collection/shard/node
> params are present becomes based on the value of the property being set,
> which is all equally arbitrary.
> The other interesting thing is that setting an arbitrary property on a node
> would allow one to mess things up royally by, say, changing properties like
> "core", or "base_url" or node_name at will. Actually this is potentially
> useful, but very, very dangerous and I'm not particularly interested in
> supporting it ;). I suppose we could require a prefix, say the only settable
> properties are "property.whatever".
> We could also add something specific to nodes, something like
> ADDREPLICAROLE/DELETEREPLICAROLE, perhaps with sub-params like
> "onlyOneAllowedPerShard", but this gets messy and relies on the users "doing
> the right thing". I prefer enforcing rules like this based on the role I
> think. Or at least enforcing these kinds of requirements on the
> "preferredLeader" role if we go that way.
> What are people's thoughts here? I think I'm tending towards the
> ADDREPLICAROLE/DELETEREPLICAROLE way of doing this, but it's not set in
> stone. I have code locally for arbitrary properties that I can modify for the
> role bits.
> So, if I'm going to summarize the points I'd like feedback on:
> 1> Is setting arbitrary properties on a node desirable? If so, should we
> require a prefix like "property" to prevent resetting values SolrCloud
> depends on?
> 2> Is it better to piggyback on ADDROLE/DELETEROLE? Personally I'm not in
> favor of this one. Too messy with requiring additional parameters to work
> right in this case
> 3> Is the best option to create new collections API calls for
> ADDREPLICAROLE/DELETEREPLICAROLE that
> 3.1> require collection/slice/node parameters
> 3.2> enforces the "onlyOnePerShard" rule for certain known roles
> 3.3 v1> allows users to specify arbitrary roles something like
> "onlyOnePerShard" as an optional T|F parameter, otherwise is totally open.
> -or-
> 3.3 v2> No support other than "preferredLeader", only roles that are
> pre-defined are allowed, in which case the "onlyOnePerShard" is implicit in
> the role.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
