[james-project] 05/07: [ADR] Recompute mailbox quotas

[bt...@apache.org]

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commit a3e2064a0f04e0846b1d051b75271b7f7aa493f9
Author: Benoit Tellier <bt...@linagora.com>
AuthorDate: Fri Apr 3 12:36:30 2020 +0700

    [ADR] Recompute mailbox quotas
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 src/adr/0028-Recompute-mailbox-quotas.md | 47 ++++++++++++++++++++++++++++++++
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+# 28. Recompute mailbox quotas
+
+Date: 2020-04-03
+
+## Status
+
+Accepted (lazy consensus)
+
+## Context
+
+JMAP custom quota extension, as well as IMAP [RFC-2087](https://tools.ietf.org/html/rfc2087) enables a user to monitor
+the amount of space and message count he is allowed to use, and that he is effectively using.
+
+To track the quota values a user is effectively using, James relies on the 
+[eventBus](../site/markdown/server/manage-guice-distributed-james.md#mailbox-event-bus) to increment a Cassandra counter
+corresponding to this user.
+
+However, upon Cassandra failure, this value can be incorrect, hence the need of correcting it.
+
+## Data model details
+
+Table: imapUidTable: Holds mailbox and flags for each message, lookup by message ID
+
+Table: messageV2: Holds message metadata, independently of any mailboxes. Content of messages is stored in `blobs` 
+       and `blobparts` tables.
+       
+Table: currentQuota: Holds per quota-root current values. Quota-roots defines groups of mailboxes which share quotas 
+limitations.
+
+Operation:
+ - Quota updates are done asynchronously (event bus + listener) for successful mailbox operations.
+   - If the quota update is not applied, then we are inconsistent
+   - EventBus errors are retried upon errors, counters being non-indempotent, this can result in inconsistent quotas
+
+## Decision
+
+We will implement a generic corrective task exposed via webadmin.
+
+This task can reuse the `CurrentQuotaCalculator` and call it for each and every quotaRoot of each user.
+
+This way, non-Cassandra implementation will also benefit from this task.
+
+## Consequences
+
+This task is not concurrent-safe. Concurrent operations will result in an invalid quota to be persisted.
+
+However, as the source of truth is not altered, re-running this task will eventually return the correct result.
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