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Posted to notifications@james.apache.org by rc...@apache.org on 2020/10/12 07:40:16 UTC
[james-project] 09/12: JAMES-3406 About denormalization consistency
This is an automated email from the ASF dual-hosted git repository.
rcordier pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/james-project.git
commit 1db5dcd890cd62ce70d33a1ba91b09ff34527649
Author: Benoit Tellier <bt...@linagora.com>
AuthorDate: Wed Oct 7 09:16:07 2020 +0700
JAMES-3406 About denormalization consistency
---
.../distributed/architecture/consistency-model.adoc | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/docs/modules/servers/pages/distributed/architecture/consistency-model.adoc b/docs/modules/servers/pages/distributed/architecture/consistency-model.adoc
index 2df93ac..c4ed785 100644
--- a/docs/modules/servers/pages/distributed/architecture/consistency-model.adoc
+++ b/docs/modules/servers/pages/distributed/architecture/consistency-model.adoc
@@ -61,15 +61,23 @@ TODO
== Denormalization
-TODO
+In Cassandra, data needs to be structured to match the read patterns. To support several conflicting
+read patterns, the data needs to be duplicated into different structures. This process is called
+denormalization.
-=== Solve Inconsistency tasks
+While data can be consistent at the table level, some inconsistencies can sneak in at the applicative
+level across denormalization tables.
-TODO
+We write to a "table of truth" first, then duplicate the data to denormalization tables.
-=== Read repairs
+The Distributed server offers several mechanism to mitigate these inconsistencies:
-TODO
+ - Writes to denormalization tables are retried.
+ - Some xref:distributed/operate/guide.adoc#_solving_cassandra_inconsistencies[SolveInconsistencies tasks] are exposed and are able to heal a given denormalization table.
+They reset the "deduplication tables" content to the "table of truth" content.
+ - link:https://github.com/apache/james-project/blob/master/src/adr/0042-applicative-read-repairs.md[Read repairs],
+when implemented for a given denormalization, enables auto-healing. When an inconsistency is detected, They reset the
+"deduplication tables" entry to the "table of truth" entry.
== Consistency across data stores
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