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https://issues.apache.org/jira/browse/HBASE-5335?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13203280#comment-13203280
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Nicolas Spiegelberg commented on HBASE-5335:
--------------------------------------------
@stack: I understand why some users might want this capability for 'important'
toggles that they make frequently. I think that should be discussed as a
separate JIRA. At FB (and probably other production companies), we have a
chicken & egg problem where we don't know which seemingly-obscure values might
be useful because we don't have an easy way to toggle them online (hence the
JIRA). Most of our use cases, we'd alter the table maybe every month or two
with a new, obscure config value that we want to change, so online schema
change is acceptable since we incur minimal latency and no downtime.
Basically, our ZK use case was a UserID->ClusterID mapping for every FB user
(large # of ZNodes). This had horrible scaling problems, even when we employed
batching. I'm not a great point of contact for this, but I can get you in
contact with one. As a rule of thumb, we've been cautious about adding too
many ZNodes in the same way that you'd have an HBase admin be cautious about
adding too many regions.
> Dynamic Schema Configurations
> -----------------------------
>
> Key: HBASE-5335
> URL: https://issues.apache.org/jira/browse/HBASE-5335
> Project: HBase
> Issue Type: New Feature
> Reporter: Nicolas Spiegelberg
> Assignee: Nicolas Spiegelberg
> Labels: configuration, schema
>
> Currently, the ability for a core developer to add per-table & per-CF
> configuration settings is very heavyweight. You need to add a reserved
> keyword all the way up the stack & you have to support this variable
> long-term if you're going to expose it explicitly to the user. This has
> ended up with using Configuration.get() a lot because it is lightweight and
> you can tweak settings while you're trying to understand system behavior
> [since there are many config params that may never need to be tuned]. We
> need to add the ability to put & read arbitrary KV settings in the HBase
> schema. Combined with online schema change, this will allow us to safely
> iterate on configuration settings.
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