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https://issues.apache.org/jira/browse/CASSANDRA-18617?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17737404#comment-17737404
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dan jatnieks commented on CASSANDRA-18617:
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Part of this change is to add converters that will take the old threshold
value, including the number of system keyspaces/tables, and convert that to a
guardrail value that excludes system keyspaces/tables.
To determine the number of system keyspaces, there is an existing
{{SchemaConstants.getSystemKeyspaces}} method that seems reasonable to use.
However, I'm finding it harder to find an existing way to get the number of
system tables.
Some test code uses {{metadata}} method in system keyspace classes to get
metadata including the tables, e.g. {{{}SystemKeyspace.metadata{}}}. However,
aside from maybe doing more work than is needed, this doesn't work when called
from converter code because just accessing {{SystemKeyspace}} triggers static
initialization, and at some point that leads to needing some value from
{{{}DatabaseDescriptor{}}}. But the initialization of {{DatabaseDescriptor}} is
what triggered the loading of the config in the first place (so it ends up with
an NPE trying to access an uninitialized field).
So I think something is needed similar to {{getSystemKeyspaces}} also located
in {{SchemaConstants}} where static initialization problems are less likely. A
downside to this approach is that it depends on being updated whenever a new
system table is added, but I supposed it's no worse than the existing situation
with {{{}getSystemKeyspaces{}}}.
> Disable the deprecated keyspace/table thresholds and convert them to
> Guardrails
> -------------------------------------------------------------------------------
>
> Key: CASSANDRA-18617
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18617
> Project: Cassandra
> Issue Type: Improvement
> Components: Feature/Guardrails
> Reporter: dan jatnieks
> Assignee: dan jatnieks
> Priority: Normal
> Fix For: 5.x
>
>
> The non-guardrail thresholds 'keyspace_count_warn_threshold' and
> 'table_count_warn_threshold' configuration settings were first added with
> CASSANDRA-16309 in 4.0-beta4 and have subsequently been deprecated since
> 4.1-alpha in CASSANDRA-17195 when they were replaced/migrated to guardrails
> as part of CEP-3 (Guardrails).
> These thresholds should now be removed from cassandra.yaml, while still
> allowed in existing yaml files.
> The old thresholds will be disabled by removing their default values from
> Config.java, and any existing values for these thresholds will be converted
> to the new guardrails using the '@Replaces' tag on the corresponding
> guardrail values.
> Since the old thresholds considered the number of system keyspace/tables in
> their values, the '@Replaces' conversion will subtract the current number of
> system tables from the old value and log a descriptive message.
> See dev list discussion:
> https://lists.apache.org/thread/0zjg08hrd6xv7lhvo96frz456b2rvr8b
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