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https://issues.apache.org/jira/browse/CASSANDRA-18042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17640728#comment-17640728
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Andres de la Peña commented on CASSANDRA-18042:
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Thanks, looks good to me, +1 if CI finishes ok.
We should also wait a bit to see if others are also happy with the naming
convention. That convention should in principle be used for other similar
future guardrails. That includes the case of adding configurable warnings to
existing enable flags, which should be very easy thanks to this patch :)
Just a nit, in the spirit of CASSANDRA-17967 we should probably add to
{{cassandra.yaml}} a brief explanation of why the guardrail exists. That
explanation would be very similar, if not identical, to the {{reason}}
attribute used in the guardrail. So, for example
{code}
# Guardrail to warn and/or enable a CREATE or ALTER TABLE statement when
default_time_to_live is set to 0
# and the table is using TimeWindowCompactionStrategy compaction or a subclass
of it.
# It is suspicious to use default_time_to_live set to 0 with
TimeWindowCompactionStrategy because the data that hasn't
# been inserted or updated with a TTL will not start to automatically expire
after they are older than a respective
# compaction window unit of a certain size.
#zero_ttl_on_twcs_warned: true
#zero_ttl_on_twcs_enabled: true
{code}
> Implement a guardrail for not having zero default ttl on tables with TWCS
> -------------------------------------------------------------------------
>
> Key: CASSANDRA-18042
> URL: https://issues.apache.org/jira/browse/CASSANDRA-18042
> Project: Cassandra
> Issue Type: Improvement
> Components: Feature/Guardrails, Legacy/Core
> Reporter: Stefan Miklosovic
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 4.x
>
> Time Spent: 3h
> Remaining Estimate: 0h
>
> A user was surprised that his data have not started to expire after 90 days
> on his TWCS, he noticed that default_time_to_live on the table was set to 0
> (by accident from his side) and inserts were using TTL = 0 too.
> It is questionable why it it possible to create a table with TWCS and enable
> a user to specify default_time_to_live to be zero.
> On the other hand, I would argue that having default_time_to_live set to 0 on
> TWCS does not necessarily mean that such combination is illegal. It is about
> people just using that with advantage very often so tables are compacted away
> nicely. However, that does not have to mean that they could not use it with
> 0. But I yet have to see a use-case where TWCS was used and default ttl was
> set to 0 on purpose. Merely looking into Cassandra codebase, there are only
> cases when this parameter is not 0.
> There are three approaches:
> 1) just reject such statements (for CreateTable and AlterTable statements)
> where default_time_to_live = 0
> 2) Implement a guardrail for 1) so it can be enabled / disabled on demand
> 3) Leave possibility to set default_time_to_live to 0 on a table but make a
> guardrail for UpdateStatement so it might reject queries for tables with
> default_time_to_live is zero and for which its TTL (on that update statement)
> is set to 0 too.
> I would be careful about making the current configuration illegal because of
> backward compatibility. For that reason 2) makes the most sense to me.
> Maybe implementing 3) would make sense as well. There might be a table which
> has default ttl set to 0 as it expects a user to supply TTL every time.
> However, as it is not currently enforced anywhere, a client might still
> insert TTLs to be set to 0 even by accident.
> POC for 2) is here
> https://github.com/instaclustr/cassandra/commit/0b4dcc3d3deeffa393c02a3b80e27482007f9579
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