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new 233b784002 [ADR-68] Mutualize Cassandra storage for Quota (#1692)
233b784002 is described below
commit 233b784002f21fcd3e5a56faeb0192843a7b4b32
Author: Benoit TELLIER <btell...@linagora.com>
AuthorDate: Wed Aug 23 22:29:53 2023 +0700
[ADR-68] Mutualize Cassandra storage for Quota (#1692)
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+# 68. Mutualize Cassandra storage for Quota
+
+Date: 2023-08-18
+
+## Status
+
+Accepted (lazy consensus).
+
+Not implemented yet.
+
+## Context
+
+One generic threat is resource abuse. Meaning a user uses an unfair amount of
resources.
+
+Similarily resource limitation is a way to decrease operating costs.
+
+Quota, standardized in IMAP via
[RFC-9208](https://www.rfc-editor.org/rfc/rfc9208.html) and in JMAP via
+[RFC-9425](https://datatracker.ietf.org/doc/rfc9425/) are a mechanism designed
to keep track of
+user current usage of the resource and match it against the stored limit.
+
+Resource limitation is a broad use case that we might want to better enforce
in Apache James. This is especially
+important when operating in SaaS mode, and actual users might be badly
intentionned. See
+[ADR-67 Quota for JMAP uploads](0067-quota-for-jmap-uploads.md).
+
+As such, there is duplication, especially at the storage layers. Similar
features might benefit from mutualized storage.
+
+Especially, it is worth mentionning that Cassandra tables do not come for
free: we have a strong incentive to reduce their count.
+See [The Last Pickle blog post on this
topic](https://thelastpickle.com/blog/2020/11/25/impacts-of-many-tables-on-cassandra.html).
+
+In particular (quote from the above article):
+
+```
+If some tables share the same columns, it could be interesting to merge them
into a single one,
+adding a column to the partition key to distinguish data belonging to
different tables.
+```
+
+## Decision
+
+Add Cassandra storage helpers, exposing a generic interface for Cassandra
quota implementation of various services to mutualize their
+storage. This relies on a part of the primary key allowing to distinguish the
component.
+
+
+
+The helper will consist of 2 tables:
+- One composed of counters to track current value
+- One composed of regular `long` to track limits
+
+(one can not mix counters and regular values in the same table in Cassandra).
+
+Port exising Cassandra implementations of quota for various services to use
those helpers. Namely the Cassandra mailbox, Sieve storage. Use those
+helpers to implement JMAP quota uploads.
+
+## Consequences
+
+We expect a small decrease of the count of tables in our Cassandra schema,
going from 7 (one for mailbox quota current value, one for mailbox quota
+per user limit, one for mailbox quota per domain limit, one for mailbox quota
global limit, one for Sieve uota current value, one for Sieve quota
+per user limit, one for Sieve Quota global limit, one for JMAP uploads current
value) to just 2 (helper tables: one for current value, one for limits).
+
+We expect to make it easier to implement quota related features in the future.
+
+We need to set up Cassandra migration tasks and to record the schema upgrade
into the upgrade instructions. A compaibility mode will need to be
+explicitly configured in order to run the migration.
+
+## Alternatives
+
+Keep the current, exploded table structure and either do not care about table
count increase or do not implement further important resource limitation
+use cases.
+
+## References
+
+- [JIRA](https://issues.apache.org/jira/projects/JAMES/issues/JAMES-3926)
+- [PR of the ADR](https://github.com/apache/james-project/pull/1692)
+- [The last pickle article: impacts of many tables in a Cassandra daa
model](https://thelastpickle.com/blog/2020/11/25/impacts-of-many-tables-on-cassandra.html)
+- [RFC-9208 IMAP quotas](https://www.rfc-editor.org/rfc/rfc9208.html)
+- [RFC-9425 JMAP quotas](https://datatracker.ietf.org/doc/rfc9425/)
+- [ADR-67 Quota for JMAP uploads](0067-quota-for-jmap-uploads.md)
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